new lint: unquoted_uri

flake.nix

@@ -98,6 +98,7 @@
         mkShell rec {
           nativeBuildInputs = [
             cargo-watch
+            rust-analyzer
             toolchain
           ];
           RUST_LOG = "info";

lib/src/lints.rs

@@ -12,4 +12,5 @@ lint_map! {
     unquoted_splice,
     empty_pattern,
     redundant_pattern_bind,
+    unquoted_uri,
 }

lib/src/lints/unquoted_uri.rs

@@ -0,0 +1,63 @@
+use crate::{make, Metadata, Report, Rule, Suggestion};
+
+use if_chain::if_chain;
+use macros::lint;
+use rnix::{types::TypedNode, NodeOrToken, SyntaxElement, SyntaxKind};
+
+/// ## What it does
+/// Checks for URI expressions that are not quoted.
+///
+/// ## Why is this bad?
+/// The Nix language has a special syntax for URLs even though quoted
+/// strings can also be used to represent them. Unlike paths, URLs do
+/// not have any special properties in the Nix expression language
+/// that would make the difference useful. Moreover, using variable
+/// expansion in URLs requires some URLs to be quoted strings anyway.
+/// So the most consistent approach is to always use quoted strings to
+/// represent URLs. Additionally, a semicolon immediately after the
+/// URL can be mistaken for a part of URL by language-agnostic tools
+/// such as terminal emulators.
+///
+/// See RFC 00045 [1] for more.
+///
+/// [1]: https://github.com/NixOS/rfcs/blob/master/rfcs/0045-deprecate-url-syntax.md
+///
+/// ## Example
+///
+/// ```nix
+/// inputs = {
+///   gitignore.url = github:hercules-ci/gitignore.nix;
+/// }
+/// ```
+///
+/// Quote the URI expression:
+///
+/// ```nix
+/// inputs = {
+///   gitignore.url = "github:hercules-ci/gitignore.nix";
+/// }
+/// ```
+#[lint(
+    name = "unquoted uri",
+    note = "Found unquoted URI expression",
+    code = 12,
+    match_with = SyntaxKind::TOKEN_URI
+)]
+struct UnquotedUri;
+
+impl Rule for UnquotedUri {
+    fn validate(&self, node: &SyntaxElement) -> Option<Report> {
+        if_chain! {
+            if let NodeOrToken::Token(token) = node;
+            then {
+                let parent_node = token.parent();
+                let at = token.text_range();
+                let replacement = make::quote(&parent_node).node().clone();
+                let message = "Consider quoting this URI expression";
+                Some(self.report().suggest(at, message, Suggestion::new(at, replacement)))
+            } else {
+                None
+            }
+        }
+    }
+}