Improve module parse error

crates/compiler/load/tests/test_reporting.rs

@@ -6458,6 +6458,39 @@ All branches in an `if` must have the same type!
         )
     }
 
+    #[test]
+    fn unneeded_module_name() {
+        report_header_problem_as(
+            indoc!(
+                r"
+                module foobar []
+                "
+            ),
+            indoc!(
+                r#"
+                ── WEIRD MODULE NAME in /code/proj/Main.roc ────────────────────────────────────
+
+                I am partway through parsing a header, but I got stuck here:
+
+                1│  module foobar []
+                           ^
+
+                I am expecting a list of exports like
+
+                    module [func, value]
+
+                or module params like
+
+                    module { echo } -> [func, value]
+
+                If you're trying to specify a module name, recall that unlike
+                application names, module names are not specified in the header.
+                Instead, they are derived from the name of the module's filename.
+            "#
+            ),
+        )
+    }
+
     test_report!(
         apply_unary_negative,
         indoc!(

crates/reporting/src/error/parse.rs

@@ -4100,6 +4100,41 @@ fn to_exposes_report<'a>(
 
         EExposes::Space(error, pos) => to_space_report(alloc, lines, filename, &error, pos),
 
+        EExposes::ListStart(pos@Position { offset: 7 }) => {
+            let surroundings = Region::new(start, pos);
+            let region = LineColumnRegion::from_pos(lines.convert_pos(pos));
+
+            let doc = alloc.stack([
+                alloc.reflow(r"I am partway through parsing a header, but I got stuck here:"),
+                alloc.region_with_subregion(lines.convert_region(surroundings), region, severity),
+                alloc.concat([
+                    alloc.reflow("I am expecting a list of exports like"),
+                ]),
+                alloc
+                    .parser_suggestion("module [func, value]")
+                    .indent(4),
+                alloc.concat([
+                alloc.reflow("or module params like"),
+                ]),
+                alloc
+                    .parser_suggestion("module { echo } -> [func, value]")
+                    .indent(4),
+                alloc.concat([
+                        alloc.reflow("If you're trying to specify a module name, recall that unlike "),
+                        alloc.reflow("application names, module names are not specified in the header. "),
+                        alloc.reflow("Instead, they are derived from the name of the module's filename."),
+                ]),
+            ]);
+
+
+            Report {
+                filename,
+                doc,
+                title: "WEIRD MODULE NAME".to_string(),
+                severity,
+            }
+        },
+
         // If you're adding or changing syntax, please handle the case with a
         // good error message above instead of adding more unhandled cases below.
         EExposes::Open(pos) |