Tip replacing <- with : for static values

crates/ast/src/constrain.rs

@@ -289,6 +289,7 @@ pub fn constrain_expr<'a>(
             let fn_reason = Reason::FnCall {
                 name: opt_symbol,
                 arity: args.len() as u8,
+                called_via: *called_via,
             };
 
             let fn_con = constrain_expr(arena, env, call_expr, fn_expected, region);

crates/compiler/can/src/operator.rs

@@ -315,7 +315,7 @@ pub fn desugar_expr<'a>(arena: &'a Bump, loc_expr: &'a Loc<Expr<'a>>) -> &'a Loc
                         let args = std::slice::from_ref(arena.alloc(apply));
 
                         apply = arena.alloc(Loc {
-                            value: Apply(desugared_expr, args, *called_via),
+                            value: Apply(desugared_expr, args, CalledVia::RecordBuilder),
                             region: loc_expr.region,
                         });
                     }

crates/compiler/constrain/src/expr.rs

@@ -466,6 +466,7 @@ pub fn constrain_expr(
             let fn_reason = Reason::FnCall {
                 name: opt_symbol,
                 arity: loc_args.len() as u8,
+                called_via: *called_via,
             };
 
             let fn_con = constrain_expr(

crates/compiler/module/src/called_via.rs

@@ -88,6 +88,10 @@ pub enum CalledVia {
     /// This call is the result of desugaring string interpolation,
     /// e.g. "\(first) \(last)" is transformed into Str.concat (Str.concat first " ") last.
     StringInterpolation,
+
+    /// This call is the result of desugaring a Record Builder field.
+    /// e.g. succeed { a <- get "a" } is transformed into (get "a") (succeed \a -> { a })
+    RecordBuilder,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]

crates/compiler/types/src/types.rs

@@ -3566,6 +3566,7 @@ pub enum Reason {
     FnCall {
         name: Option<Symbol>,
         arity: u8,
+        called_via: CalledVia,
     },
     LowLevelOpArg {
         op: LowLevel,

crates/reporting/src/error/type.rs

@@ -1138,7 +1138,11 @@ fn to_expr_report<'b>(
                     ),
                 }
             }
-            Reason::FnCall { name, arity } => match describe_wanted_function(&found) {
+            Reason::FnCall {
+                name,
+                arity,
+                called_via,
+            } => match describe_wanted_function(&found) {
                 DescribedFunction::NotAFunction(tag) => {
                     let this_value = match name {
                         None => alloc.text("This value"),
@@ -1174,7 +1178,21 @@ fn to_expr_report<'b>(
                                 )),
                             ]),
                             alloc.region(lines.convert_region(expr_region)),
-                            alloc.reflow("Are there any missing commas? Or missing parentheses?"),
+                            match called_via {
+                                CalledVia::RecordBuilder => {
+                                    alloc.concat([
+                                        alloc.tip(),
+                                        alloc.reflow("Replace "),
+                                        alloc.keyword("<-"),
+                                        alloc.reflow(" with "),
+                                        alloc.keyword(":"),
+                                        alloc.reflow(" to assign the field directly.")
+                                    ])
+                                }
+                                _ => {
+                                    alloc.reflow("Are there any missing commas? Or missing parentheses?")
+                                }
+                            }
                         ]),
                     };
 

crates/reporting/tests/test_reporting.rs

@@ -10225,6 +10225,29 @@ I recommend using camelCase. It's the standard style in Roc code!
     "###
     );
 
+    test_report!(
+        record_builder_apply_non_function,
+        indoc!(
+            r#"
+            succeed = \_ -> crash ""
+
+            succeed { 
+                a <- "a",
+            }
+            "#
+        ),
+        @r###"
+    ── TOO MANY ARGS ───────────────────────────────────────── /code/proj/Main.roc ─
+
+    This value is not a function, but it was given 1 argument:
+
+    7│          a <- "a",
+                     ^^^
+
+    Tip: Replace `<-` with `:` to assign the field directly.
+    "###
+    );
+
     test_report!(
         destructure_assignment_introduces_no_variables_nested,
         indoc!(