New module header

Implements the new `module` header syntax as described in "module and package changes" [1]:

```
module [Request, Response, req]
```

The old syntax should still work fine, and is automatically upgraded to the new one
when running `roc format`.

[1] https://docs.google.com/document/d/1E_77fO-44BtoBtXoVeWyGh1xN2KRTWTu8q6i25RNNx0/edit

crates/cli/src/format.rs

@@ -8,7 +8,6 @@ use roc_fmt::def::fmt_defs;
 use roc_fmt::module::fmt_module;
 use roc_fmt::spaces::RemoveSpaces;
 use roc_fmt::{Ast, Buf};
-use roc_parse::ast::Defs;
 use roc_parse::module::parse_module_defs;
 use roc_parse::{module, parser::SyntaxError, state::State};
 
@@ -226,7 +225,9 @@ fn parse_all<'a>(arena: &'a Bump, src: &'a str) -> Result<Ast<'a>, SyntaxError<'
     let (module, state) = module::parse_header(arena, State::new(src.as_bytes()))
         .map_err(|e| SyntaxError::Header(e.problem))?;
 
-    let defs = parse_module_defs(arena, state, Defs::default())?;
+    let (module, defs) = module.upgrade_header_imports(arena);
+
+    let defs = parse_module_defs(arena, state, defs)?;
 
     Ok(Ast { module, defs })
 }

crates/compiler/builtins/roc/Bool.roc

@@ -1,6 +1,4 @@
-interface Bool
+module [Bool, Eq, true, false, and, or, not, isEq, isNotEq]
-    exposes [Bool, Eq, true, false, and, or, not, isEq, isNotEq]
-    imports []
 
 ## Defines a type that can be compared for total equality.
 ##

crates/compiler/builtins/roc/Box.roc

@@ -2,9 +2,7 @@
 ## - Holding unknown Roc types when developing [platforms](https://github.com/roc-lang/roc/wiki/Roc-concepts-explained#platform).
 ## - To improve performance in rare cases.
 ##
-interface Box
+module [box, unbox]
-    exposes [box, unbox]
-    imports []
 
 ## Allocates a value on the heap. Boxing is an expensive process as it copies
 ## the value from the stack to the heap. This may provide a performance

crates/compiler/builtins/roc/Decode.roc

@@ -1,5 +1,4 @@
-interface Decode
+module [
-    exposes [
     DecodeError,
     DecodeResult,
     Decoder,
@@ -30,7 +29,6 @@ interface Decode
     fromBytes,
     mapResult,
 ]
-    imports []
 
 import List
 import Result exposing [Result]

crates/compiler/builtins/roc/Dict.roc

@@ -1,5 +1,4 @@
-interface Dict
+module [
-    exposes [
     Dict,
     empty,
     withCapacity,
@@ -29,7 +28,6 @@ interface Dict
     map,
     joinMap,
 ]
-    imports []
 
 import Bool exposing [Bool, Eq]
 import Result exposing [Result]

crates/compiler/builtins/roc/Encode.roc

@@ -1,5 +1,4 @@
-interface Encode
+module [
-    exposes [
     Encoder,
     Encoding,
     toEncoder,
@@ -28,7 +27,6 @@ interface Encode
     append,
     toBytes,
 ]
-    imports []
 
 import Num exposing [
     U8,

crates/compiler/builtins/roc/Hash.roc

@@ -1,5 +1,4 @@
-interface Hash
+module [
-    exposes [
     Hash,
     Hasher,
     hash,
@@ -20,7 +19,7 @@ interface Hash
     hashStrBytes,
     hashList,
     hashUnordered,
-    ] imports []
+]
 
 import Bool exposing [Bool]
 import List

crates/compiler/builtins/roc/Inspect.roc

@@ -1,5 +1,4 @@
-interface Inspect
+module [
-    exposes [
     Inspect,
     Inspector,
     InspectFormatter,
@@ -35,7 +34,6 @@ interface Inspect
     toInspector,
     toStr,
 ]
-    imports []
 
 import Bool exposing [Bool]
 import Num exposing [U8, U16, U32, U64, U128, I8, I16, I32, I64, I128, F32, F64, Dec]

crates/compiler/builtins/roc/List.roc

@@ -1,5 +1,4 @@
-interface List
+module [
-    exposes [
     isEmpty,
     get,
     set,
@@ -71,7 +70,6 @@ interface List
     countIf,
     chunksOf,
 ]
-    imports []
 
 import Bool exposing [Bool, Eq]
 import Result exposing [Result]

crates/compiler/builtins/roc/Num.roc

@@ -1,5 +1,4 @@
-interface Num
+module [
-    exposes [
     Num,
     Int,
     Frac,
@@ -157,7 +156,6 @@ interface Num
     f32FromParts,
     f64FromParts,
 ]
-    imports []
 
 import Bool exposing [Bool]
 import Result exposing [Result]

crates/compiler/builtins/roc/Result.roc

@@ -1,6 +1,4 @@
-interface Result
+module [Result, isOk, isErr, map, mapErr, try, onErr, withDefault]
-    exposes [Result, isOk, isErr, map, mapErr, try, onErr, withDefault]
-    imports []
 
 import Bool exposing [Bool]
 

crates/compiler/builtins/roc/Set.roc

@@ -1,5 +1,4 @@
-interface Set
+module [
-    exposes [
     Set,
     empty,
     withCapacity,
@@ -24,7 +23,6 @@ interface Set
     map,
     joinMap,
 ]
-    imports []
 
 import List
 import Bool exposing [Bool, Eq]

crates/compiler/builtins/roc/Str.roc

@@ -326,8 +326,7 @@
 ## If a situation like this comes up, a slice can be turned into a separate string by using [`Str.concat`](https://www.roc-lang.org/builtins/Str#concat) to concatenate the slice onto an empty string (or one created with [`Str.withCapacity`](https://www.roc-lang.org/builtins/Str#withCapacity)).
 ##
 ## Currently, the only way to get seamless slices of strings is by calling certain `Str` functions which return them. In general, `Str` functions which accept a string and return a subset of that string tend to do this. [`Str.trim`](https://www.roc-lang.org/builtins/Str#trim) is another example of a function which returns a seamless slice.
-interface Str
+module [
-    exposes [
     Utf8Problem,
     Utf8ByteProblem,
     concat,
@@ -369,7 +368,6 @@ interface Str
     withPrefix,
     contains,
 ]
-    imports []
 
 import Bool exposing [Bool]
 import Result exposing [Result]

crates/compiler/builtins/roc/TotallyNotJson.roc

@@ -1,12 +1,10 @@
 ## THIS MODULE IS DEPRECATED AND CURRENTLY IN THE PROCESS OF BEING REMOVED
 ## FROM STD LIBRARY
-interface TotallyNotJson
+module [
-    exposes [
     Json,
     json,
     jsonWithOptions,
 ]
-    imports []
 
 import List
 import Str

crates/compiler/can/src/def.rs

@@ -506,7 +506,7 @@ fn canonicalize_claimed_ability_impl<'a>(
             // OPTION-1: The implementation identifier is the only identifier of that name in the
             //           scope. For example,
             //
-            //               interface F imports [] exposes []
+            //               module []
             //
             //               Hello := {} implements [Encoding.{ toEncoder }]
             //
@@ -518,7 +518,9 @@ fn canonicalize_claimed_ability_impl<'a>(
             // OPTION-2: The implementation identifier is a unique shadow of the ability member,
             //           which has also been explicitly imported. For example,
             //
-            //               interface F imports [Encoding.{ toEncoder }] exposes []
+            //               module []
+            //
+            //               import Encoding exposing [toEncoder]
             //
             //               Hello := {} implements [Encoding.{ toEncoder }]
             //

crates/compiler/fmt/src/module.rs

@@ -8,7 +8,7 @@ use bumpalo::Bump;
 use roc_parse::ast::{Collection, Header, Module, Spaced, Spaces};
 use roc_parse::header::{
     AppHeader, ExposedName, ExposesKeyword, GeneratesKeyword, HostedHeader, ImportsEntry,
-    ImportsKeyword, InterfaceHeader, Keyword, KeywordItem, ModuleName, PackageEntry, PackageHeader,
+    ImportsKeyword, Keyword, KeywordItem, ModuleHeader, ModuleName, PackageEntry, PackageHeader,
     PackageKeyword, PackageName, PackagesKeyword, PlatformHeader, PlatformRequires,
     ProvidesKeyword, ProvidesTo, RequiresKeyword, To, ToKeyword, TypedIdent, WithKeyword,
 };
@@ -18,8 +18,8 @@ use roc_region::all::Loc;
 pub fn fmt_module<'a>(buf: &mut Buf<'_>, module: &'a Module<'a>) {
     fmt_comments_only(buf, module.comments.iter(), NewlineAt::Bottom, 0);
     match &module.header {
-        Header::Interface(header) => {
+        Header::Module(header) => {
-            fmt_interface_header(buf, header);
+            fmt_module_header(buf, header);
         }
         Header::App(header) => {
             fmt_app_header(buf, header);
@@ -171,20 +171,19 @@ impl<'a, K: Formattable, V: Formattable> Formattable for KeywordItem<'a, K, V> {
     }
 }
 
-pub fn fmt_interface_header<'a>(buf: &mut Buf, header: &'a InterfaceHeader<'a>) {
+pub fn fmt_module_header<'a>(buf: &mut Buf, header: &'a ModuleHeader<'a>) {
     buf.indent(0);
-    buf.push_str("interface");
+    buf.push_str("module");
+
+    if header.before_exposes.iter().all(|c| c.is_newline()) {
+        buf.spaces(1);
+        fmt_exposes(buf, header.exposes, 0);
+    } else {
         let indent = INDENT;
-    fmt_default_spaces(buf, header.before_name, indent);
 
-    // module name
+        fmt_default_spaces(buf, header.before_exposes, indent);
-    buf.indent(indent);
+        fmt_exposes(buf, header.exposes, indent);
-    buf.push_str(header.name.value.as_str());
+    };
-
-    header.exposes.keyword.format(buf, indent);
-    fmt_exposes(buf, header.exposes.item, indent);
-    header.imports.keyword.format(buf, indent);
-    fmt_imports(buf, header.imports.item, indent);
 }
 
 pub fn fmt_hosted_header<'a>(buf: &mut Buf, header: &'a HostedHeader<'a>) {

crates/compiler/fmt/src/spaces.rs

@@ -10,9 +10,9 @@ use roc_parse::{
         StrSegment, Tag, TypeAnnotation, TypeDef, TypeHeader, ValueDef, WhenBranch,
     },
     header::{
-        AppHeader, ExposedName, HostedHeader, ImportsEntry, InterfaceHeader, KeywordItem,
+        AppHeader, ExposedName, HostedHeader, ImportsEntry, KeywordItem, ModuleHeader, ModuleName,
-        ModuleName, PackageEntry, PackageHeader, PackageName, PlatformHeader, PlatformRequires,
+        PackageEntry, PackageHeader, PackageName, PlatformHeader, PlatformRequires, ProvidesTo, To,
-        ProvidesTo, To, TypedIdent,
+        TypedIdent,
     },
     ident::{BadIdent, UppercaseIdent},
 };
@@ -283,11 +283,10 @@ impl<'a> RemoveSpaces<'a> for ProvidesTo<'a> {
 impl<'a> RemoveSpaces<'a> for Module<'a> {
     fn remove_spaces(&self, arena: &'a Bump) -> Self {
         let header = match &self.header {
-            Header::Interface(header) => Header::Interface(InterfaceHeader {
+            Header::Module(header) => Header::Module(ModuleHeader {
-                before_name: &[],
+                before_exposes: &[],
-                name: header.name.remove_spaces(arena),
                 exposes: header.exposes.remove_spaces(arena),
-                imports: header.imports.remove_spaces(arena),
+                interface_imports: header.interface_imports.remove_spaces(arena),
             }),
             Header::App(header) => Header::App(AppHeader {
                 before_name: &[],

crates/compiler/load/tests/test_reporting.rs

@@ -6109,9 +6109,7 @@ In roc, functions are always written as a lambda, like{}
         report_header_problem_as(
             indoc!(
                 r"
-                interface Foobar
+                module [main, @Foo]
-                    exposes [main, @Foo]
-                    imports [pf.Task, Base64]
                 "
             ),
             indoc!(
@@ -6120,39 +6118,12 @@ In roc, functions are always written as a lambda, like{}
 
                 I am partway through parsing an `exposes` list, but I got stuck here:
 
-                1│  interface Foobar
+                1│  module [main, @Foo]
-                2│      exposes [main, @Foo]
                                   ^
 
                 I was expecting a type name, value name or function name next, like
 
-                    exposes [Animal, default, tame]
+                    [Animal, default, tame]
-            "
-            ),
-        )
-    }
-
-    #[test]
-    fn invalid_module_name() {
-        report_header_problem_as(
-            indoc!(
-                r"
-                interface foobar
-                    exposes [main, @Foo]
-                    imports [pf.Task, Base64]
-                "
-            ),
-            indoc!(
-                r"
-                ── WEIRD MODULE NAME in /code/proj/Main.roc ────────────────────────────────────
-
-                I am partway through parsing a header, but got stuck here:
-
-                1│  interface foobar
-                              ^
-
-                I am expecting a module name next, like BigNum or Main. Module names
-                must start with an uppercase letter.
             "
             ),
         )

crates/compiler/load_internal/src/file.rs

@@ -49,8 +49,8 @@ use roc_mono::{drop_specialization, inc_dec};
 use roc_packaging::cache::RocCacheDir;
 use roc_parse::ast::{self, CommentOrNewline, ExtractSpaces, Spaced, ValueDef};
 use roc_parse::header::{
-    ExposedName, HeaderType, ImportsKeywordItem, PackageEntry, PackageHeader, PlatformHeader, To,
+    self, ExposedName, HeaderType, ImportsKeywordItem, PackageEntry, PackageHeader, PlatformHeader,
-    TypedIdent,
+    To, TypedIdent,
 };
 use roc_parse::module::parse_module_defs;
 use roc_parse::parser::{FileError, SourceError, SyntaxError};
@@ -644,7 +644,7 @@ struct CanAndCon {
 enum PlatformPath<'a> {
     NotSpecified,
     Valid(To<'a>),
-    RootIsInterface,
+    RootIsModule,
     RootIsHosted,
     RootIsPlatformModule,
 }
@@ -1204,8 +1204,9 @@ fn adjust_header_paths<'a>(
     {
         debug_assert_eq!(*header_id, header_output.module_id);
 
-        if let HeaderType::Interface { name, .. } = header_type {
+        if let HeaderType::Module { name, .. } = header_type {
-            // Interface modules can have names like Foo.Bar.Baz,
+            // [modules-revamp] TODO: Privacy changes
+            // Modules can have names like Foo.Bar.Baz,
             // in which case we need to adjust the src_dir to
             // remove the "Bar/Baz" directories in order to correctly
             // resolve this interface module's imports!
@@ -2313,13 +2314,13 @@ fn update<'a>(
                             state.exposed_modules = exposes_ids;
                         }
                     }
-                    Builtin { .. } | Interface { .. } => {
+                    Builtin { .. } | Module { .. } => {
                         if header.is_root_module {
                             debug_assert!(matches!(
                                 state.platform_path,
                                 PlatformPath::NotSpecified
                             ));
-                            state.platform_path = PlatformPath::RootIsInterface;
+                            state.platform_path = PlatformPath::RootIsModule;
                         }
                     }
                     Hosted { .. } => {
@@ -2956,7 +2957,7 @@ fn update<'a>(
                     // This happens due to abilities. In detail, consider
                     //
                     //   # Default module
-                    //   interface Default exposes [default, getDefault]
+                    //   module [default, getDefault]
                     //
                     //   Default implements default : {} -> a where a implements Default
                     //
@@ -3198,7 +3199,7 @@ fn finish_specialization<'a>(
     let module_id = state.root_id;
     let uses_prebuilt_platform = match platform_data {
         Some(data) => data.is_prebuilt,
-        // If there's no platform data (e.g. because we're building an interface module)
+        // If there's no platform data (e.g. because we're building a module)
         // then there's no prebuilt platform either!
         None => false,
     };
@@ -3346,12 +3347,12 @@ fn load_package_from_disk<'a>(
             match parsed {
                 Ok((
                     ast::Module {
-                        header: ast::Header::Interface(header),
+                        header: ast::Header::Module(header),
                         ..
                     },
                     _parse_state,
                 )) => Err(LoadingProblem::UnexpectedHeader(format!(
-                    "expected platform/package module, got Interface with header\n{header:?}"
+                    "expected platform/package module, got Module with header\n{header:?}"
                 ))),
                 Ok((
                     ast::Module {
@@ -3477,23 +3478,25 @@ fn load_builtin_module_help<'a>(
     match parsed {
         Ok((
             ast::Module {
-                header: ast::Header::Interface(header),
+                header: ast::Header::Module(header),
                 comments,
             },
             parse_state,
         )) => {
+            let name_stem = arena.alloc_str(filename.file_stem().unwrap().to_str().unwrap());
+
             let info = HeaderInfo {
                 filename,
                 is_root_module,
                 opt_shorthand,
                 packages: &[],
                 header_type: HeaderType::Builtin {
-                    name: header.name.value,
+                    name: header::ModuleName::new(name_stem),
-                    exposes: unspace(arena, header.exposes.item.items),
+                    exposes: unspace(arena, header.exposes.items),
                     generates_with: &[],
                 },
                 module_comments: comments,
-                header_imports: Some(header.imports),
+                header_imports: header.interface_imports,
             };
 
             (info, parse_state)
@@ -3693,45 +3696,6 @@ fn find_task<T>(local: &Worker<T>, global: &Injector<T>, stealers: &[Stealer<T>]
     })
 }
 
-fn verify_interface_matches_file_path<'a>(
-    interface_name: Loc<roc_parse::header::ModuleName<'a>>,
-    path: &Path,
-    state: &roc_parse::state::State<'a>,
-) -> Result<(), LoadingProblem<'a>> {
-    let module_parts = interface_name.value.as_str().split(MODULE_SEPARATOR).rev();
-
-    let mut is_mismatched = false;
-    let mut opt_path = Some(path);
-    for part in module_parts {
-        match opt_path.and_then(|path| path.file_stem().map(|fi| (path, fi))) {
-            None => {
-                is_mismatched = true;
-                break;
-            }
-            Some((path, fi)) => {
-                if fi != part {
-                    is_mismatched = true;
-                    break;
-                }
-                opt_path = path.parent();
-            }
-        }
-    }
-
-    if !is_mismatched {
-        return Ok(());
-    }
-
-    use roc_parse::parser::EHeader;
-    let syntax_problem =
-        SyntaxError::Header(EHeader::InconsistentModuleName(interface_name.region));
-    let problem = LoadingProblem::ParsingFailed(FileError {
-        problem: SourceError::new(syntax_problem, state),
-        filename: path.to_path_buf(),
-    });
-    Err(problem)
-}
-
 #[derive(Debug)]
 struct HeaderOutput<'a> {
     module_id: ModuleId,
@@ -3798,48 +3762,35 @@ fn parse_header<'a>(
     match parsed {
         Ok((
             ast::Module {
-                header: ast::Header::Interface(header),
+                header: ast::Header::Module(header),
                 comments,
             },
             parse_state,
         )) => {
-            verify_interface_matches_file_path(header.name, &filename, &parse_state)?;
+            let module_name = match opt_expected_module_name {
+                Some(pq_name) => arena.alloc_str(pq_name.as_inner().as_str()),
+                None => {
+                    // [modules-revamp] [privacy-changes] TODO: Support test/check on nested modules
+                    arena.alloc_str(filename.file_stem().unwrap().to_str().unwrap())
+                }
+            };
 
-            let header_name_region = header.name.region;
             let info = HeaderInfo {
                 filename,
                 is_root_module,
                 opt_shorthand,
                 packages: &[],
-                header_type: HeaderType::Interface {
+                header_type: HeaderType::Module {
-                    name: header.name.value,
+                    name: roc_parse::header::ModuleName::new(module_name),
-                    exposes: unspace(arena, header.exposes.item.items),
+                    exposes: unspace(arena, header.exposes.items),
                 },
                 module_comments: comments,
-                header_imports: Some(header.imports),
+                header_imports: header.interface_imports,
             };
 
-            let (module_id, module_name, header) =
+            let (module_id, _, header) =
                 build_header(info, parse_state.clone(), module_ids, module_timing)?;
 
-            if let Some(expected_module_name) = opt_expected_module_name {
-                if expected_module_name != module_name {
-                    let problem = SourceError::new(
-                        IncorrectModuleName {
-                            module_id,
-                            found: Loc::at(header_name_region, module_name),
-                            expected: expected_module_name,
-                        },
-                        &parse_state,
-                    );
-                    let problem = LoadingProblem::IncorrectModuleName(FileError {
-                        problem,
-                        filename: header.module_path,
-                    });
-                    return Err(problem);
-                }
-            }
-
             Ok(HeaderOutput {
                 module_id,
                 msg: Msg::Header(header),
@@ -4217,14 +4168,9 @@ fn build_header<'a>(
             // Package modules do not have names.
             String::new().into()
         }
-        HeaderType::Interface { name, .. }
+        HeaderType::Module { name, .. }
         | HeaderType::Builtin { name, .. }
-        | HeaderType::Hosted { name, .. } => {
+        | HeaderType::Hosted { name, .. } => name.as_str().into(),
-            // TODO check to see if name is consistent with filename.
-            // If it isn't, report a problem!
-
-            name.as_str().into()
-        }
     };
 
     let (name, home) = {
@@ -5172,7 +5118,7 @@ fn parse<'a>(
         }
         HeaderType::App { .. }
         | HeaderType::Package { .. }
-        | HeaderType::Interface { .. }
+        | HeaderType::Module { .. }
         | HeaderType::Builtin { .. }
         | HeaderType::Hosted { .. } => {}
     };
@@ -6408,12 +6354,12 @@ fn report_cannot_run(
                     severity: Severity::RuntimeError,
                 }
             }
-            RootIsInterface => {
+            RootIsModule => {
                 let doc = alloc.stack([
                     alloc.reflow(
-                        r"The input file is an `interface` module, but only `app` modules can be run.",
+                        r"The input file is a module, but only `app` modules can be run.",
                     ),
-                    alloc.reflow(r"Tip: You can use `roc check` or `roc test` to verify an interface module like this one."),
+                    alloc.reflow(r"Tip: You can use `roc check` or `roc test` to verify a module like this one."),
                 ]);
 
                 Report {

crates/compiler/load_internal/tests/test_load.rs

@@ -339,7 +339,7 @@ fn import_transitive_alias() {
             "RBTree.roc",
             indoc!(
                 r"
-                        interface RBTree exposes [RedBlackTree, empty] imports []
+                        module [RedBlackTree, empty]
 
                         # The color of a node. Leaves are considered Black.
                         NodeColor : [Red, Black]
@@ -357,7 +357,7 @@ fn import_transitive_alias() {
             "Other.roc",
             indoc!(
                 r"
-                        interface Other exposes [empty] imports []
+                        module [empty]
 
                         import RBTree
 
@@ -372,9 +372,9 @@ fn import_transitive_alias() {
 }
 
 #[test]
-fn interface_with_deps() {
+fn module_with_deps() {
     let subs_by_module = Default::default();
-    let src_dir = fixtures_dir().join("interface_with_deps");
+    let src_dir = fixtures_dir().join("module_with_deps");
     let filename = src_dir.join("Primary.roc");
     let arena = Bump::new();
     let loaded = load_and_typecheck(
@@ -488,7 +488,7 @@ fn load_docs() {
 #[test]
 fn import_alias() {
     let subs_by_module = Default::default();
-    let loaded_module = load_fixture("interface_with_deps", "ImportAlias", subs_by_module);
+    let loaded_module = load_fixture("module_with_deps", "ImportAlias", subs_by_module);
 
     expect_types(
         loaded_module,
@@ -501,7 +501,7 @@ fn import_alias() {
 #[test]
 fn import_inside_def() {
     let subs_by_module = Default::default();
-    let loaded_module = load_fixture("interface_with_deps", "ImportInsideDef", subs_by_module);
+    let loaded_module = load_fixture("module_with_deps", "ImportInsideDef", subs_by_module);
 
     expect_types(
         loaded_module,
@@ -517,7 +517,7 @@ fn import_inside_def() {
 fn exposed_used_outside_scope() {
     let subs_by_module = Default::default();
     load_fixture(
-        "interface_with_deps",
+        "module_with_deps",
         "ExposedUsedOutsideScope",
         subs_by_module,
     );
@@ -527,17 +527,13 @@ fn exposed_used_outside_scope() {
 #[should_panic(expected = "MODULE NOT IMPORTED")]
 fn import_used_outside_scope() {
     let subs_by_module = Default::default();
-    load_fixture(
+    load_fixture("module_with_deps", "ImportUsedOutsideScope", subs_by_module);
-        "interface_with_deps",
-        "ImportUsedOutsideScope",
-        subs_by_module,
-    );
 }
 
 #[test]
 fn test_load_and_typecheck() {
     let subs_by_module = Default::default();
-    let loaded_module = load_fixture("interface_with_deps", "WithBuiltins", subs_by_module);
+    let loaded_module = load_fixture("module_with_deps", "WithBuiltins", subs_by_module);
 
     expect_types(
         loaded_module,
@@ -558,7 +554,7 @@ fn test_load_and_typecheck() {
 #[test]
 fn iface_quicksort() {
     let subs_by_module = Default::default();
-    let loaded_module = load_fixture("interface_with_deps", "Quicksort", subs_by_module);
+    let loaded_module = load_fixture("module_with_deps", "Quicksort", subs_by_module);
 
     expect_types(
         loaded_module,
@@ -574,7 +570,7 @@ fn iface_quicksort() {
 #[test]
 fn load_astar() {
     let subs_by_module = Default::default();
-    let loaded_module = load_fixture("interface_with_deps", "AStar", subs_by_module);
+    let loaded_module = load_fixture("module_with_deps", "AStar", subs_by_module);
 
     expect_types(
         loaded_module,
@@ -606,7 +602,7 @@ fn load_principal_types() {
 #[test]
 fn iface_dep_types() {
     let subs_by_module = Default::default();
-    let loaded_module = load_fixture("interface_with_deps", "Primary", subs_by_module);
+    let loaded_module = load_fixture("module_with_deps", "Primary", subs_by_module);
 
     expect_types(
         loaded_module,
@@ -650,7 +646,7 @@ fn app_dep_types() {
 #[test]
 fn imported_dep_regression() {
     let subs_by_module = Default::default();
-    let loaded_module = load_fixture("interface_with_deps", "OneDep", subs_by_module);
+    let loaded_module = load_fixture("module_with_deps", "OneDep", subs_by_module);
 
     expect_types(
         loaded_module,
@@ -663,7 +659,7 @@ fn imported_dep_regression() {
 #[test]
 fn ingested_file() {
     let subs_by_module = Default::default();
-    let loaded_module = load_fixture("interface_with_deps", "IngestedFile", subs_by_module);
+    let loaded_module = load_fixture("module_with_deps", "IngestedFile", subs_by_module);
 
     expect_types(
         loaded_module,
@@ -678,7 +674,7 @@ fn ingested_file() {
 #[test]
 fn ingested_file_bytes() {
     let subs_by_module = Default::default();
-    let loaded_module = load_fixture("interface_with_deps", "IngestedFileBytes", subs_by_module);
+    let loaded_module = load_fixture("module_with_deps", "IngestedFileBytes", subs_by_module);
 
     expect_types(
         loaded_module,
@@ -695,7 +691,7 @@ fn parse_problem() {
         "Main.roc",
         indoc!(
             r"
-                interface Main exposes [main] imports []
+                module [main]
 
                 main = [
                 "
@@ -732,7 +728,7 @@ fn parse_problem() {
 #[should_panic(expected = "FILE NOT FOUND")]
 fn file_not_found() {
     let subs_by_module = Default::default();
-    let loaded_module = load_fixture("interface_with_deps", "invalid$name", subs_by_module);
+    let loaded_module = load_fixture("module_with_deps", "invalid$name", subs_by_module);
 
     expect_types(
         loaded_module,
@@ -887,7 +883,7 @@ fn opaque_wrapped_unwrapped_outside_defining_module() {
             "Age.roc",
             indoc!(
                 r"
-                    interface Age exposes [Age] imports []
+                    module [Age]
 
                     Age := U32
                     "
@@ -897,7 +893,7 @@ fn opaque_wrapped_unwrapped_outside_defining_module() {
             "Main.roc",
             indoc!(
                 r"
-                    interface Main exposes [twenty, readAge] imports []
+                    module [twenty, readAge]
 
                     import Age exposing [Age]
 
@@ -965,7 +961,8 @@ fn unused_imports() {
             "Dep1.roc",
             indoc!(
                 r#"
-                interface Dep1 exposes [one] imports []
+                module [one]
+
                 one = 1
                 "#
             ),
@@ -974,7 +971,8 @@ fn unused_imports() {
             "Dep2.roc",
             indoc!(
                 r#"
-                interface Dep2 exposes [two] imports []
+                module [two]
+
                 two = 2
                 "#
             ),
@@ -983,7 +981,7 @@ fn unused_imports() {
             "Dep3.roc",
             indoc!(
                 r#"
-                interface Dep3 exposes [Three, three] imports []
+                module [Three, three]
 
                 Three : [Three]
 
@@ -995,7 +993,7 @@ fn unused_imports() {
             "Main.roc",
             indoc!(
                 r#"
-            interface Main exposes [usedModule, unusedModule, unusedExposed, unusedWithAlias, usingThreeValue] imports []
+            module [usedModule, unusedModule, unusedExposed, usingThreeValue, unusedWithAlias]
 
             import Dep1
             import Dep3 exposing [Three]
@@ -1663,48 +1661,13 @@ fn import_builtin_in_platform_and_check_app() {
     assert!(result.is_ok(), "should check");
 }
 
-#[test]
-fn module_doesnt_match_file_path() {
-    let modules = vec![(
-        "Age.roc",
-        indoc!(
-            r"
-                interface NotAge exposes [Age] imports []
-
-                Age := U32
-                "
-        ),
-    )];
-
-    let err = multiple_modules("module_doesnt_match_file_path", modules).unwrap_err();
-    assert_eq!(
-        err,
-        indoc!(
-            r"
-            ── WEIRD MODULE NAME in tmp/module_doesnt_match_file_path/Age.roc ──────────────
-
-            This module name does not correspond with the file path it is defined
-            in:
-
-            1│  interface NotAge exposes [Age] imports []
-                          ^^^^^^
-
-            Module names must correspond with the file paths they are defined in.
-            For example, I expect to see BigNum defined in BigNum.roc, or Math.Sin
-            defined in Math/Sin.roc."
-        ),
-        "\n{}",
-        err
-    );
-}
-
 #[test]
 fn module_cyclic_import_itself() {
     let modules = vec![(
         "Age.roc",
         indoc!(
             r"
-            interface Age exposes [] imports []
+            module []
 
             import Age
             "
@@ -1742,7 +1705,8 @@ fn module_cyclic_import_transitive() {
             "Age.roc",
             indoc!(
                 r"
-                interface Age exposes [] imports []
+                module []
+
                 import Person
                 "
             ),
@@ -1751,7 +1715,8 @@ fn module_cyclic_import_transitive() {
             "Person.roc",
             indoc!(
                 r"
-                interface Person exposes [] imports []
+                module []
+                
                 import Age
                 "
             ),

crates/compiler/parse/src/ast.rs

@@ -1,7 +1,7 @@
 use std::fmt::Debug;
 
 use crate::header::{
-    self, AppHeader, HostedHeader, InterfaceHeader, ModuleName, PackageHeader, PlatformHeader,
+    self, AppHeader, HostedHeader, ModuleHeader, ModuleName, PackageHeader, PlatformHeader,
 };
 use crate::ident::Accessor;
 use crate::parser::ESingleQuote;
@@ -99,6 +99,21 @@ pub struct Module<'a> {
 }
 
 impl<'a> Module<'a> {
+    pub fn upgrade_header_imports(self, arena: &'a Bump) -> (Self, Defs<'a>) {
+        let (header, defs) = match self.header {
+            Header::Module(header) => (
+                Header::Module(ModuleHeader {
+                    interface_imports: None,
+                    ..header
+                }),
+                Self::header_imports_to_defs(arena, header.interface_imports),
+            ),
+            header => (header, Defs::default()),
+        };
+
+        (Module { header, ..self }, defs)
+    }
+
     pub fn header_imports_to_defs(
         arena: &'a Bump,
         imports: Option<
@@ -209,7 +224,7 @@ impl<'a> Module<'a> {
 
 #[derive(Clone, Debug, PartialEq)]
 pub enum Header<'a> {
-    Interface(InterfaceHeader<'a>),
+    Module(ModuleHeader<'a>),
     App(AppHeader<'a>),
     Package(PackageHeader<'a>),
     Platform(PlatformHeader<'a>),
@@ -2272,7 +2287,7 @@ impl<'a> Malformed for Module<'a> {
 impl<'a> Malformed for Header<'a> {
     fn is_malformed(&self) -> bool {
         match self {
-            Header::Interface(header) => header.is_malformed(),
+            Header::Module(header) => header.is_malformed(),
             Header::App(header) => header.is_malformed(),
             Header::Package(header) => header.is_malformed(),
             Header::Platform(header) => header.is_malformed(),

crates/compiler/parse/src/header.rs

@@ -19,7 +19,7 @@ impl<'a> HeaderType<'a> {
             }
             | HeaderType::Hosted { exposes, .. }
             | HeaderType::Builtin { exposes, .. }
-            | HeaderType::Interface { exposes, .. } => exposes,
+            | HeaderType::Module { exposes, .. } => exposes,
             HeaderType::Platform { .. } | HeaderType::Package { .. } => &[],
         }
     }
@@ -30,7 +30,7 @@ impl<'a> HeaderType<'a> {
             HeaderType::Builtin { .. } => "builtin",
             HeaderType::Package { .. } => "package",
             HeaderType::Platform { .. } => "platform",
-            HeaderType::Interface { .. } => "interface",
+            HeaderType::Module { .. } => "module",
         }
     }
 }
@@ -73,7 +73,7 @@ pub enum HeaderType<'a> {
         /// usually `pf`
         config_shorthand: &'a str,
     },
-    Interface {
+    Module {
         name: ModuleName<'a>,
         exposes: &'a [Loc<ExposedName<'a>>],
     },
@@ -82,9 +82,9 @@ pub enum HeaderType<'a> {
 impl<'a> HeaderType<'a> {
     pub fn get_name(self) -> Option<&'a str> {
         match self {
-            Self::Interface { name, .. }
+            Self::Module { name, .. } | Self::Builtin { name, .. } | Self::Hosted { name, .. } => {
-            | Self::Builtin { name, .. }
+                Some(name.into())
-            | Self::Hosted { name, .. } => Some(name.into()),
+            }
             Self::App {
                 output_name: StrLiteral::PlainLine(name),
                 ..
@@ -106,13 +106,11 @@ impl<'a> HeaderType<'a> {
 
     pub fn to_maybe_builtin(self, module_id: ModuleId) -> Self {
         match self {
-            HeaderType::Interface { name, exposes } if module_id.is_builtin() => {
+            HeaderType::Module { name, exposes } if module_id.is_builtin() => HeaderType::Builtin {
-                HeaderType::Builtin {
                 name,
                 exposes,
                 generates_with: &[],
-                }
+            },
-            }
             _ => self,
         }
     }
@@ -246,12 +244,12 @@ pub struct KeywordItem<'a, K, V> {
 }
 
 #[derive(Clone, Debug, PartialEq)]
-pub struct InterfaceHeader<'a> {
+pub struct ModuleHeader<'a> {
-    pub before_name: &'a [CommentOrNewline<'a>],
+    pub before_exposes: &'a [CommentOrNewline<'a>],
-    pub name: Loc<ModuleName<'a>>,
+    pub exposes: Collection<'a, Loc<Spaced<'a, ExposedName<'a>>>>,
 
-    pub exposes: KeywordItem<'a, ExposesKeyword, Collection<'a, Loc<Spaced<'a, ExposedName<'a>>>>>,
+    // Keeping this so we can format old interface header into module headers
-    pub imports: KeywordItem<'a, ImportsKeyword, Collection<'a, Loc<Spaced<'a, ImportsEntry<'a>>>>>,
+    pub interface_imports: Option<KeywordItem<'a, ImportsKeyword, ImportsCollection<'a>>>,
 }
 
 pub type ImportsKeywordItem<'a> = KeywordItem<'a, ImportsKeyword, ImportsCollection<'a>>;
@@ -430,7 +428,7 @@ where
     }
 }
 
-impl<'a> Malformed for InterfaceHeader<'a> {
+impl<'a> Malformed for ModuleHeader<'a> {
     fn is_malformed(&self) -> bool {
         false
     }

crates/compiler/parse/src/module.rs

@@ -1,10 +1,11 @@
-use crate::ast::{Collection, Defs, Header, Module, Spaced, Spaces};
+use crate::ast::{Collection, CommentOrNewline, Defs, Header, Module, Spaced, Spaces};
 use crate::blankspace::{space0_around_ee, space0_before_e, space0_e};
 use crate::header::{
     package_entry, package_name, AppHeader, ExposedName, ExposesKeyword, GeneratesKeyword,
-    HostedHeader, ImportsEntry, ImportsKeyword, InterfaceHeader, Keyword, KeywordItem, ModuleName,
+    HostedHeader, ImportsEntry, ImportsKeyword, ImportsKeywordItem, Keyword, KeywordItem,
-    PackageEntry, PackageHeader, PackagesKeyword, PlatformHeader, PlatformRequires,
+    ModuleHeader, ModuleName, PackageEntry, PackageHeader, PackagesKeyword, PlatformHeader,
-    ProvidesKeyword, ProvidesTo, RequiresKeyword, To, ToKeyword, TypedIdent, WithKeyword,
+    PlatformRequires, ProvidesKeyword, ProvidesTo, RequiresKeyword, To, ToKeyword, TypedIdent,
+    WithKeyword,
 };
 use crate::ident::{self, lowercase_ident, unqualified_ident, uppercase, UppercaseIdent};
 use crate::parser::Progress::{self, *};
@@ -60,12 +61,20 @@ pub fn header<'a>() -> impl Parser<'a, Module<'a>, EHeader<'a>> {
     record!(Module {
         comments: space0_e(EHeader::IndentStart),
         header: one_of![
+            map!(
+                skip_first!(
+                    keyword("module", EHeader::Start),
+                    increment_min_indent(module_header())
+                ),
+                Header::Module
+            ),
+            // Old headers
             map!(
                 skip_first!(
                     keyword("interface", EHeader::Start),
                     increment_min_indent(interface_header())
                 ),
-                Header::Interface
+                Header::Module
             ),
             map!(
                 skip_first!(
@@ -100,22 +109,65 @@ pub fn header<'a>() -> impl Parser<'a, Module<'a>, EHeader<'a>> {
 }
 
 #[inline(always)]
-fn interface_header<'a>() -> impl Parser<'a, InterfaceHeader<'a>, EHeader<'a>> {
+fn module_header<'a>() -> impl Parser<'a, ModuleHeader<'a>, EHeader<'a>> {
-    record!(InterfaceHeader {
+    record!(ModuleHeader {
-        before_name: space0_e(EHeader::IndentStart),
+        before_exposes: space0_e(EHeader::IndentStart),
-        name: loc!(module_name_help(EHeader::ModuleName)),
+        exposes: specialize_err(EHeader::Exposes, exposes_list()),
-        exposes: specialize_err(EHeader::Exposes, exposes_values()),
+        interface_imports: succeed!(None)
-        imports: specialize_err(EHeader::Imports, imports()),
+    })
+    .trace("module_header")
+}
+
+/// Parse old interface headers so we can format them into module headers
+#[inline(always)]
+fn interface_header<'a>() -> impl Parser<'a, ModuleHeader<'a>, EHeader<'a>> {
+    use bumpalo::collections::Vec;
+
+    let before_exposes = map_with_arena!(
+        and!(
+            skip_second!(
+                space0_e(EHeader::IndentStart),
+                loc!(module_name_help(EHeader::ModuleName))
+            ),
+            specialize_err(EHeader::Exposes, exposes_kw())
+        ),
+        |arena: &'a bumpalo::Bump,
+         (before_name, kw): (&'a [CommentOrNewline<'a>], Spaces<'a, ExposesKeyword>)| {
+            let mut combined: Vec<CommentOrNewline> =
+                Vec::with_capacity_in(before_name.len() + kw.before.len() + kw.after.len(), arena);
+            combined.extend(before_name);
+            combined.extend(kw.before);
+            combined.extend(kw.after);
+            arena.alloc(combined)
+        }
+    );
+
+    record!(ModuleHeader {
+        before_exposes: before_exposes,
+        exposes: specialize_err(EHeader::Exposes, exposes_list()).trace("exposes_list"),
+        interface_imports: map!(
+            specialize_err(EHeader::Imports, imports()),
+            imports_none_if_empty
+        )
+        .trace("imports"),
     })
     .trace("interface_header")
 }
 
+fn imports_none_if_empty(value: ImportsKeywordItem<'_>) -> Option<ImportsKeywordItem<'_>> {
+    if value.item.is_empty() {
+        None
+    } else {
+        Some(value)
+    }
+}
+
 #[inline(always)]
 fn hosted_header<'a>() -> impl Parser<'a, HostedHeader<'a>, EHeader<'a>> {
     record!(HostedHeader {
         before_name: space0_e(EHeader::IndentStart),
         name: loc!(module_name_help(EHeader::ModuleName)),
-        exposes: specialize_err(EHeader::Exposes, exposes_values()),
+        exposes: specialize_err(EHeader::Exposes, exposes_values_kw()),
         imports: specialize_err(EHeader::Imports, imports()),
         generates: specialize_err(EHeader::Generates, generates()),
         generates_with: specialize_err(EHeader::GeneratesWith, generates_with()),
@@ -388,26 +440,37 @@ fn requires_typed_ident<'a>() -> impl Parser<'a, Loc<Spaced<'a, TypedIdent<'a>>>
 }
 
 #[inline(always)]
-fn exposes_values<'a>() -> impl Parser<
+fn exposes_values_kw<'a>() -> impl Parser<
     'a,
     KeywordItem<'a, ExposesKeyword, Collection<'a, Loc<Spaced<'a, ExposedName<'a>>>>>,
     EExposes,
 > {
     record!(KeywordItem {
-        keyword: spaces_around_keyword(
+        keyword: exposes_kw(),
+        item: exposes_list()
+    })
+}
+
+#[inline(always)]
+fn exposes_kw<'a>() -> impl Parser<'a, Spaces<'a, ExposesKeyword>, EExposes> {
+    spaces_around_keyword(
         ExposesKeyword,
         EExposes::Exposes,
         EExposes::IndentExposes,
-            EExposes::IndentListStart
+        EExposes::IndentListStart,
-        ),
+    )
-        item: collection_trailing_sep_e!(
+}
+
+#[inline(always)]
+fn exposes_list<'a>() -> impl Parser<'a, Collection<'a, Loc<Spaced<'a, ExposedName<'a>>>>, EExposes>
+{
+    collection_trailing_sep_e!(
         byte(b'[', EExposes::ListStart),
         exposes_entry(EExposes::Identifier),
         byte(b',', EExposes::ListEnd),
         byte(b']', EExposes::ListEnd),
         Spaced::SpaceBefore
     )
-    })
 }
 
 pub fn spaces_around_keyword<'a, K: Keyword, E>(

crates/compiler/test_syntax/tests/snapshots/pass/empty_interface_header.header.formatted.roc

@@ -1 +0,0 @@
-interface Foo exposes [] imports []

crates/compiler/test_syntax/tests/snapshots/pass/empty_interface_header.header.result-ast

@@ -1,27 +0,0 @@
-Module {
-    comments: [],
-    header: Interface(
-        InterfaceHeader {
-            before_name: [],
-            name: @10-13 ModuleName(
-                "Foo",
-            ),
-            exposes: KeywordItem {
-                keyword: Spaces {
-                    before: [],
-                    item: ExposesKeyword,
-                    after: [],
-                },
-                item: [],
-            },
-            imports: KeywordItem {
-                keyword: Spaces {
-                    before: [],
-                    item: ImportsKeyword,
-                    after: [],
-                },
-                item: [],
-            },
-        },
-    ),
-}

crates/compiler/test_syntax/tests/snapshots/pass/empty_interface_header.header.roc

@@ -1 +0,0 @@
-interface Foo exposes [] imports []

crates/compiler/test_syntax/tests/snapshots/pass/empty_module_header.header.formatted.roc

@@ -0,0 +1 @@
+module []

crates/compiler/test_syntax/tests/snapshots/pass/empty_module_header.header.result-ast

@@ -0,0 +1,10 @@
+Module {
+    comments: [],
+    header: Module(
+        ModuleHeader {
+            before_exposes: [],
+            exposes: [],
+            interface_imports: None,
+        },
+    ),
+}

crates/compiler/test_syntax/tests/snapshots/pass/empty_module_header.header.roc

@@ -0,0 +1 @@
+module []

crates/compiler/test_syntax/tests/snapshots/pass/interface_with_newline.header.formatted.roc

@@ -1 +0,0 @@
-interface T exposes [] imports []

crates/compiler/test_syntax/tests/snapshots/pass/interface_with_newline.header.result-ast

@@ -1,27 +0,0 @@
-Module {
-    comments: [],
-    header: Interface(
-        InterfaceHeader {
-            before_name: [],
-            name: @10-11 ModuleName(
-                "T",
-            ),
-            exposes: KeywordItem {
-                keyword: Spaces {
-                    before: [],
-                    item: ExposesKeyword,
-                    after: [],
-                },
-                item: [],
-            },
-            imports: KeywordItem {
-                keyword: Spaces {
-                    before: [],
-                    item: ImportsKeyword,
-                    after: [],
-                },
-                item: [],
-            },
-        },
-    ),
-}

crates/compiler/test_syntax/tests/snapshots/pass/interface_with_newline.header.roc

@@ -1 +0,0 @@
-interface T exposes [] imports []

crates/compiler/test_syntax/tests/snapshots/pass/module_multiline_exposes.header.formatted.roc

@@ -0,0 +1,5 @@
+module [
+    a,
+    b,
+    c,
+]

crates/compiler/test_syntax/tests/snapshots/pass/module_multiline_exposes.header.result-ast

@@ -0,0 +1,25 @@
+Module {
+    comments: [],
+    header: Module(
+        ModuleHeader {
+            before_exposes: [],
+            exposes: [
+                @8-9 ExposedName(
+                    "a",
+                ),
+                @11-12 ExposedName(
+                    "b",
+                ),
+                @18-19 SpaceBefore(
+                    ExposedName(
+                        "c",
+                    ),
+                    [
+                        Newline,
+                    ],
+                ),
+            ],
+            interface_imports: None,
+        },
+    ),
+}

crates/compiler/test_syntax/tests/snapshots/pass/module_multiline_exposes.header.roc

@@ -0,0 +1,2 @@
+module [a, b,
+    c]

crates/compiler/test_syntax/tests/snapshots/pass/module_with_newline.header.formatted.roc

@@ -0,0 +1 @@
+module []

crates/compiler/test_syntax/tests/snapshots/pass/module_with_newline.header.result-ast

@@ -0,0 +1,10 @@
+Module {
+    comments: [],
+    header: Module(
+        ModuleHeader {
+            before_exposes: [],
+            exposes: [],
+            interface_imports: None,
+        },
+    ),
+}

crates/compiler/test_syntax/tests/snapshots/pass/module_with_newline.header.roc

@@ -0,0 +1 @@
+module []

crates/compiler/test_syntax/tests/snapshots/pass/nested_module.header.formatted.roc

@@ -1 +0,0 @@
-interface Foo.Bar.Baz exposes [] imports []

crates/compiler/test_syntax/tests/snapshots/pass/nested_module.header.result-ast

@@ -1,27 +0,0 @@
-Module {
-    comments: [],
-    header: Interface(
-        InterfaceHeader {
-            before_name: [],
-            name: @10-21 ModuleName(
-                "Foo.Bar.Baz",
-            ),
-            exposes: KeywordItem {
-                keyword: Spaces {
-                    before: [],
-                    item: ExposesKeyword,
-                    after: [],
-                },
-                item: [],
-            },
-            imports: KeywordItem {
-                keyword: Spaces {
-                    before: [],
-                    item: ImportsKeyword,
-                    after: [],
-                },
-                item: [],
-            },
-        },
-    ),
-}

crates/compiler/test_syntax/tests/snapshots/pass/nested_module.header.roc

@@ -1 +0,0 @@
-interface Foo.Bar.Baz exposes [] imports []

crates/compiler/test_syntax/tests/snapshots/pass/old_interface_header.header.formatted.roc

@@ -0,0 +1 @@
+module [Foo, foo, bar]

crates/compiler/test_syntax/tests/snapshots/pass/old_interface_header.header.result-ast

@@ -0,0 +1,20 @@
+Module {
+    comments: [],
+    header: Module(
+        ModuleHeader {
+            before_exposes: [],
+            exposes: [
+                @23-26 ExposedName(
+                    "Foo",
+                ),
+                @28-31 ExposedName(
+                    "foo",
+                ),
+                @33-36 ExposedName(
+                    "bar",
+                ),
+            ],
+            interface_imports: None,
+        },
+    ),
+}

crates/compiler/test_syntax/tests/snapshots/pass/old_interface_header.header.roc

@@ -0,0 +1 @@
+interface Foo exposes [Foo, foo, bar] imports []

crates/compiler/test_syntax/tests/test_fmt.rs

@@ -4768,10 +4768,10 @@ mod test_fmt {
     // MODULES
 
     #[test]
-    fn single_line_interface() {
+    fn single_line_module() {
         module_formats_same(indoc!(
             r"
-                interface Foo exposes [] imports []"
+                module []"
         ));
     }
 
@@ -4781,12 +4781,14 @@ mod test_fmt {
         module_formats_to(
             indoc!(
                 r"
-            interface Foo exposes [] imports []
+            module []
+
             a = 42 # Yay greetings"
             ),
             indoc!(
                 r"
-            interface Foo exposes [] imports []
+            module []
+
             a = 42 # Yay greetings
             "
             ),
@@ -4794,49 +4796,25 @@ mod test_fmt {
     }
 
     #[test]
-    fn multiline_interface() {
+    fn module_exposing() {
         module_formats_same(indoc!(
             r"
-                interface Foo
+                module [Bar, Baz, a, b]"
-                    exposes []
-                    imports []"
         ));
     }
 
     #[test]
-    fn interface_exposing() {
+    fn module_exposing_multiline() {
         module_formats_same(indoc!(
             r"
-                interface Foo
+                module [
-                    exposes [Bar, Baz, a, b]
-                    imports []"
-        ));
-    }
-
-    #[test]
-    fn interface_importing() {
-        module_formats_same(indoc!(
-            r"
-                interface Foo
-                    exposes [Bar, Baz, a, b]
-                    imports [Blah, Thing.{ foo, bar }, Stuff]"
-        ));
-    }
-
-    #[test]
-    fn multi_line_interface() {
-        module_formats_same(indoc!(
-            r"
-                interface Foo
-                    exposes [
                     Stuff,
                     Things,
                     somethingElse,
                 ]
-                    imports [
+
-                        Blah,
+                import Blah
-                        Baz.{ stuff, things },
+                import Baz exposing [stuff, things]"
-                    ]"
         ));
     }
 
@@ -4866,9 +4844,7 @@ mod test_fmt {
             &format!(
                 indoc!(
                     r#"
-                    interface Foo
+                    module []
-                        exposes []
-                        imports []
 
                     # comment 1{space}
                     def = "" # comment 2{space}
@@ -4879,9 +4855,7 @@ mod test_fmt {
             ),
             indoc!(
                 r#"
-                    interface Foo
+                    module []
-                        exposes []
-                        imports []
 
                     # comment 1
                     def = "" # comment 2
@@ -5700,7 +5674,7 @@ mod test_fmt {
 
         module_formats_same(indoc!(
             r"
-                interface Foo exposes [] imports []
+                module []
 
                 expect x == y
 
@@ -5727,7 +5701,7 @@ mod test_fmt {
 
         module_formats_same(indoc!(
             r"
-                interface Foo exposes [] imports []
+                module []
 
                 expect
                     foo bar
@@ -5831,7 +5805,7 @@ mod test_fmt {
     fn ability_member_doc_comments() {
         module_formats_same(indoc!(
             r"
-            interface Foo exposes [] imports []
+            module []
 
             A implements
                 ## This is member ab
@@ -5850,9 +5824,7 @@ mod test_fmt {
         module_formats_same(indoc!(
             r"
             # hello world
-            interface Foo
+            module []
-                exposes []
-                imports []
             "
         ));
 
@@ -5876,6 +5848,17 @@ mod test_fmt {
         ));
     }
 
+    #[test]
+    fn comments_before_exposes_preserved() {
+        module_formats_same(indoc!(
+            r"
+            module
+                # comment
+                [a, b]
+            "
+        ));
+    }
+
     #[test]
     fn clauses_with_multiple_abilities() {
         expr_formats_same(indoc!(

crates/compiler/test_syntax/tests/test_snapshots.rs

@@ -301,8 +301,8 @@ mod test_snapshots {
         pass/def_without_newline.expr,
         pass/destructure_tag_assignment.expr,
         pass/empty_app_header.header,
+        pass/empty_module_header.header,
         pass/empty_hosted_header.header,
-        pass/empty_interface_header.header,
         pass/empty_list.expr,
         pass/empty_package_header.header,
         pass/empty_platform_header.header,
@@ -333,7 +333,7 @@ mod test_snapshots {
         pass/inline_import.expr,
         pass/inline_ingested_file.expr,
         pass/int_with_underscore.expr,
-        pass/interface_with_newline.header,
+        pass/module_with_newline.header,
         pass/lambda_in_chain.expr,
         pass/lambda_indent.expr,
         pass/list_closing_indent_not_enough.expr,
@@ -348,6 +348,7 @@ mod test_snapshots {
         pass/minus_twelve_minus_five.expr,
         pass/mixed_docs.expr,
         pass/module_def_newline.moduledefs,
+        pass/module_multiline_exposes.header,
         pass/multi_backpassing.expr,
         pass/multi_backpassing_in_def.moduledefs,
         pass/multi_backpassing_with_apply.expr,
@@ -369,7 +370,6 @@ mod test_snapshots {
         pass/nested_def_annotation.moduledefs,
         pass/nested_def_without_newline.expr,
         pass/nested_if.expr,
-        pass/nested_module.header,
         pass/newline_after_equals.expr, // Regression test for https://github.com/roc-lang/roc/issues/51
         pass/newline_after_mul.expr,
         pass/newline_after_paren.expr,
@@ -409,6 +409,7 @@ mod test_snapshots {
         pass/outdented_colon_in_record.expr,
         pass/outdented_list.expr,
         pass/outdented_record.expr,
+        pass/old_interface_header.header,
         pass/packed_singleton_list.expr,
         pass/parens_in_type_def_apply.expr,
         pass/parens_in_value_def_annotation.expr,

crates/language_server/src/analysis/tokens.rs

@@ -11,9 +11,8 @@ use roc_parse::{
         WhenBranch,
     },
     header::{
-        AppHeader, ExposedName, HostedHeader, ImportsEntry, InterfaceHeader, ModuleName,
+        AppHeader, ExposedName, HostedHeader, ImportsEntry, ModuleHeader, ModuleName, PackageEntry,
-        PackageEntry, PackageHeader, PackageName, PlatformHeader, PlatformRequires, ProvidesTo, To,
+        PackageHeader, PackageName, PlatformHeader, PlatformRequires, ProvidesTo, To, TypedIdent,
-        TypedIdent,
     },
     ident::{Accessor, UppercaseIdent},
 };
@@ -202,7 +201,7 @@ impl IterTokens for Module<'_> {
 impl IterTokens for Header<'_> {
     fn iter_tokens<'a>(&self, arena: &'a Bump) -> BumpVec<'a, Loc<Token>> {
         match self {
-            Header::Interface(ih) => ih.iter_tokens(arena),
+            Header::Module(mh) => mh.iter_tokens(arena),
             Header::App(app) => app.iter_tokens(arena),
             Header::Package(pkg) => pkg.iter_tokens(arena),
             Header::Platform(pf) => pf.iter_tokens(arena),
@@ -211,19 +210,15 @@ impl IterTokens for Header<'_> {
     }
 }
 
-impl IterTokens for InterfaceHeader<'_> {
+impl IterTokens for ModuleHeader<'_> {
     fn iter_tokens<'a>(&self, arena: &'a Bump) -> BumpVec<'a, Loc<Token>> {
         let Self {
-            before_name: _,
+            before_exposes: _,
-            name,
             exposes,
-            imports,
+            interface_imports: _,
         } = self;
 
-        (name.iter_tokens(arena).into_iter())
+        exposes.iter_tokens(arena)
-            .chain(exposes.item.iter_tokens(arena))
-            .chain(imports.item.iter_tokens(arena))
-            .collect_in(arena)
     }
 }
 

crates/packaging/src/tarball.rs

@@ -128,7 +128,7 @@ fn write_archive<W: Write>(path: &Path, writer: W) -> io::Result<()> {
     // TODO use this when finding .roc files by discovering them from the root module.
     // let other_modules: &[Module<'_>] =
     match read_header(&arena, &mut buf, path)?.header {
-        Header::Interface(_) => {
+        Header::Module(_) => {
             todo!();
             // TODO report error
         }

crates/reporting/src/error/parse.rs

@@ -3621,7 +3621,7 @@ fn to_exposes_report<'a>(
                     "I was expecting a type name, value name or function name next, like",
                 )]),
                 alloc
-                    .parser_suggestion("exposes [Animal, default, tame]")
+                    .parser_suggestion("[Animal, default, tame]")
                     .indent(4),
             ]);
 
@@ -3646,7 +3646,7 @@ fn to_exposes_report<'a>(
                     alloc.reflow(" keyword next, like"),
                 ]),
                 alloc
-                    .parser_suggestion("exposes [Animal, default, tame]")
+                    .parser_suggestion("[Animal, default, tame]")
                     .indent(4),
             ]);
 

examples/Community.roc

@@ -1,5 +1,4 @@
-interface Community
+module [
-    exposes [
     Community,
     empty,
     addPerson,
@@ -7,7 +6,6 @@ interface Community
     Person,
     walkFriendNames,
 ]
-    imports []
 
 ## Datatype representing a community for demonstration purposes in inspect-gui.roc and inspect-logging.roc
 

examples/GuiFormatter.roc

@@ -1,9 +1,7 @@
-interface GuiFormatter
+module [
-    exposes [
     GuiFormatter,
     toGui,
 ]
-    imports []
 
 ## Creates GUI representations of Roc values, for use in inspect-gui.roc
 

examples/cli/false-interpreter/Context.roc

@@ -1,6 +1,8 @@
-interface Context
+module [Context, Data, with, getChar, Option, pushStack, popStack, toStr, inWhileScope]
-    exposes [Context, Data, with, getChar, Option, pushStack, popStack, toStr, inWhileScope]
+
-    imports [pf.File, pf.Task.{ Task }, Variable.{ Variable }]
+import pf.File
+import pf.Task exposing [Task]
+import Variable exposing [Variable]
 
 Option a : [Some a, None]
 

examples/cli/false-interpreter/Variable.roc

@@ -1,6 +1,4 @@
-interface Variable
+module [Variable, fromUtf8, toIndex, totalCount, toStr]
-    exposes [Variable, fromUtf8, toIndex, totalCount, toStr]
-    imports []
 
 # Variables in False can only be single letters. Thus, the valid variables are "a" to "z".
 # This opaque type deals with ensure we always have valid variables.

examples/cli/false-interpreter/platform/File.roc

@@ -1,6 +1,7 @@
-interface File
+module [line, Handle, withOpen, chunk]
-    exposes [line, Handle, withOpen, chunk]
+
-    imports [pf.Effect, Task.{ Task }]
+import pf.Effect
+import Task exposing [Task]
 
 Handle := U64
 

examples/cli/false-interpreter/platform/Stdin.roc

@@ -1,6 +1,7 @@
-interface Stdin
+module [char]
-    exposes [char]
+
-    imports [pf.Effect, Task]
+import pf.Effect
+import Task
 
 # line : Task.Task Str *
 # line = Effect.after Effect.getLine Task.succeed # TODO FIXME Effect.getLine should suffice

examples/cli/false-interpreter/platform/Stdout.roc

@@ -1,6 +1,7 @@
-interface Stdout
+module [line, raw]
-    exposes [line, raw]
+
-    imports [pf.Effect, Task.{ Task }]
+import pf.Effect
+import Task exposing [Task]
 
 line : Str -> Task {} *
 line = \str -> Effect.map (Effect.putLine str) (\_ -> Ok {})

examples/cli/false-interpreter/platform/Task.roc

@@ -1,6 +1,6 @@
-interface Task
+module [Task, succeed, fail, await, map, onFail, attempt, fromResult, loop]
-    exposes [Task, succeed, fail, await, map, onFail, attempt, fromResult, loop]
+
-    imports [pf.Effect]
+import pf.Effect
 
 Task ok err : Effect.Effect (Result ok err)
 

examples/cli/tui-platform/Program.roc

@@ -1,6 +1,4 @@
-interface Program
+module [Program]
-    exposes [Program]
-    imports []
 
 Program model : {
     init : {} -> model,

examples/gui/breakout/platform/Action.roc

@@ -1,6 +1,4 @@
-interface Action
+module [Action, none, update, map]
-    exposes [Action, none, update, map]
-    imports []
 
 Action state : [None, Update state]
 

examples/gui/breakout/platform/Elem.roc

@@ -1,6 +1,6 @@
-interface Elem
+module [Elem, PressEvent, row, col, text, button, none, translate, list]
-    exposes [Elem, PressEvent, row, col, text, button, none, translate, list]
+
-    imports [Action.{ Action }]
+import Action exposing [Action]
 
 Elem state : [
     # PERFORMANCE NOTE:

examples/gui/breakout/platform/Game.roc

@@ -1,6 +1,4 @@
-interface Game
+module [Bounds, Elem, Event]
-    exposes [Bounds, Elem, Event]
-    imports []
 
 Rgba : { r : F32, g : F32, b : F32, a : F32 }
 

examples/gui/platform/Action.roc

@@ -1,6 +1,4 @@
-interface Action
+module [Action, none, update, map]
-    exposes [Action, none, update, map]
-    imports []
 
 Action state : [None, Update state]
 

examples/gui/platform/Elem.roc

@@ -1,6 +1,6 @@
-interface Elem
+module [Elem, PressEvent, row, col, text, button, none, translate, list]
-    exposes [Elem, PressEvent, row, col, text, button, none, translate, list]
+
-    imports [Action.{ Action }]
+import Action exposing [Action]
 
 Elem state : [
     # PERFORMANCE NOTE:

examples/static-site-gen/platform/Html.roc

@@ -1,5 +1,4 @@
-interface Html
+module [
-    exposes [
     Node,
     Attribute,
     render,
@@ -122,7 +121,8 @@ interface Html
     slot,
     template,
 ]
-    imports [Html.Attributes]
+
+import Html.Attributes
 
 Node : [
     Text Str,

examples/static-site-gen/platform/Html/Attributes.roc

@@ -1,5 +1,4 @@
-interface Html.Attributes
+module [
-    exposes [
     Attribute,
     attribute,
     accept,
@@ -138,7 +137,6 @@ interface Html.Attributes
     width,
     wrap,
 ]
-    imports []
 
 Attribute : [Attribute Str Str]
 

examples/virtual-dom-wip/ExampleApp.roc

@@ -1,8 +1,6 @@
-interface ExampleApp
+module [exampleApp, State]
-    exposes [exampleApp, State]
+
-    imports [
+import pf.Html exposing [App, Html, html, head, body, div, text, h1]
-        pf.Html.{ App, Html, html, head, body, div, text, h1 },
-    ]
 
 State : {
     answer : U32,

examples/virtual-dom-wip/platform/Action.roc

@@ -1,6 +1,4 @@
-interface Action
+module [Action, none, update, map]
-    exposes [Action, none, update, map]
-    imports []
 
 Action state : [None, Update state]
 

examples/virtual-dom-wip/platform/Html.roc

@@ -1,5 +1,4 @@
-interface Html
+module [
-    exposes [
     App,
     Html,
     Attribute,
@@ -123,7 +122,9 @@ interface Html
     slot,
     template,
 ]
-    imports [Html.Internal.Shared, Html.Internal.Server]
+
+import Html.Internal.Shared
+import Html.Internal.Server
 
 App state initData : Html.Internal.Shared.App state initData
 Html state : Html.Internal.Shared.Html state

examples/virtual-dom-wip/platform/Html/Attributes.roc

@@ -1,5 +1,4 @@
-interface Html.Attributes
+module [
-    exposes [
     attribute,
     accept,
     acceptCharset,
@@ -134,7 +133,8 @@ interface Html.Attributes
     width,
     wrap,
 ]
-    imports [Html.Internal.Shared.{ Attribute }]
+
+import Html.Internal.Shared exposing [Attribute]
 
 attribute : Str -> (Str -> Attribute state)
 attribute = \attrType ->

examples/virtual-dom-wip/platform/Html/Event.roc

@@ -1,5 +1,4 @@
-interface Html.Event
+module [
-    exposes [
     Handler,
     CyclicStructureAccessor,
     on,
@@ -18,10 +17,9 @@ interface Html.Event
     onInput,
     onSubmit,
 ]
-    imports [
+
-        Action.{ Action },
+import Action exposing [Action]
-        Html.Internal.Shared.{ Attribute },
+import Html.Internal.Shared exposing [Attribute]
-    ]
 
 Handler state : Html.Internal.Shared.Handler state
 CyclicStructureAccessor : Html.Internal.Shared.CyclicStructureAccessor

examples/virtual-dom-wip/platform/Html/Internal/Client.roc

@@ -1,29 +1,27 @@
-interface Html.Internal.Client
+module [
-    exposes [
     PlatformState,
     initClientApp,
     dispatchEvent,
 ]
-    imports [
+
-        Effect.{
+import Effect exposing [
     Effect,
     NodeId,
     HandlerId,
     TagName,
     AttrType,
     EventType,
-        },
+]
-        Html.Internal.Shared.{
+import Html.Internal.Shared exposing [
     App,
     Html,
     Attribute,
     CyclicStructureAccessor,
     Handler,
     translateStatic,
-        },
-        TotallyNotJson,
-        Action,
 ]
+import TotallyNotJson
+import Action
 
 PlatformState state initData : {
     app : App state initData,

examples/virtual-dom-wip/platform/Html/Internal/Server.roc

@@ -1,12 +1,10 @@
-interface Html.Internal.Server
+module [
-    exposes [
     appendRenderedStatic,
     initServerApp,
 ]
-    imports [
+
-        Html.Internal.Shared.{ Html, Attribute, App, translateStatic, text, element },
+import Html.Internal.Shared exposing [Html, Attribute, App, translateStatic, text, element]
-        TotallyNotJson,
+import TotallyNotJson
-    ]
 
 # -------------------------------
 #   STATIC HTML

examples/virtual-dom-wip/platform/Html/Internal/Shared.roc

@@ -1,5 +1,4 @@
-interface Html.Internal.Shared
+module [
-    exposes [
     App,
     Html,
     Attribute,
@@ -13,9 +12,8 @@ interface Html.Internal.Shared
     translateStatic,
     nodeSize,
 ]
-    imports [
+
-        Action.{ Action },
+import Action exposing [Action]
-    ]
 
 App state initData : {
     init : DecodingResult initData -> state,