Report module params parse error

crates/compiler/load/tests/test_reporting.rs

@@ -6210,6 +6210,31 @@ In roc, functions are always written as a lambda, like{}
         )
     }
 
+    #[test]
+    fn module_params_with_missing_arrow() {
+        report_header_problem_as(
+            indoc!(
+                r#"
+                module {echo, read} [menu]
+                "#
+            ),
+            indoc!(
+                r#"
+                ── WEIRD MODULE PARAMS in /code/proj/Main.roc ──────────────────────────────────
+
+                I am partway through parsing a module header, but I got stuck here:
+
+                1│  module {echo, read} [menu]
+                                        ^
+
+                I am expecting `->` next, like:
+
+                    module { echo, read } -> [menu]
+                "#
+            ),
+        )
+    }
+
     #[test]
     fn platform_requires_rigids() {
         report_header_problem_as(

crates/compiler/test_syntax/tests/snapshots/fail/module_params_with_missing_arrow.header.result-ast

@@ -0,0 +1 @@
+Header(Params(Arrow(@22), @7))

crates/compiler/test_syntax/tests/snapshots/fail/module_params_with_missing_arrow.header.roc

@@ -0,0 +1 @@
+module { echo, name } [menu]

crates/compiler/test_syntax/tests/snapshots/fail/module_with_unfinished_params.header.result-ast

@@ -0,0 +1 @@
+Header(Params(Pattern(End(@20), @7), @7))

crates/compiler/test_syntax/tests/snapshots/fail/module_with_unfinished_params.header.roc

@@ -0,0 +1 @@
+module { echo, name -> [menu]

crates/compiler/test_syntax/tests/test_snapshots.rs

@@ -249,6 +249,8 @@ mod test_snapshots {
         fail/when_over_indented_underscore.expr,
         fail/where_type_variable.expr,
         fail/wild_case_arrow.expr,
+        fail/module_with_unfinished_params.header,
+        fail/module_params_with_missing_arrow.header,
         malformed/bad_opaque_ref.expr,
         malformed/malformed_ident_due_to_underscore.expr,
         malformed/malformed_pattern_field_access.expr, // See https://github.com/roc-lang/roc/issues/399

crates/reporting/src/error/parse.rs

@@ -3392,7 +3392,7 @@ fn to_header_report<'a>(
             to_provides_report(alloc, lines, filename, provides, *pos)
         }
 
-        EHeader::Params(_params, _pos) => todo!(),
+        EHeader::Params(params, pos) => to_params_report(alloc, lines, filename, params, *pos),
 
         EHeader::Exposes(exposes, pos) => to_exposes_report(alloc, lines, filename, exposes, *pos),
 
@@ -3788,6 +3788,48 @@ fn to_provides_report<'a>(
     }
 }
 
+fn to_params_report<'a>(
+    alloc: &'a RocDocAllocator<'a>,
+    lines: &LineInfo,
+    filename: PathBuf,
+    parse_problem: &roc_parse::parser::EParams<'a>,
+    start: Position,
+) -> Report<'a> {
+    use roc_parse::parser::EParams;
+
+    match parse_problem {
+        EParams::Pattern(error, pos) => to_precord_report(alloc, lines, filename, error, *pos),
+
+        EParams::BeforeArrow(pos) | EParams::Arrow(pos) | EParams::AfterArrow(pos) => {
+            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 module header, but I got stuck here:"),
+                alloc.region_with_subregion(lines.convert_region(surroundings), region),
+                alloc.concat([
+                    alloc.reflow("I am expecting "),
+                    alloc.keyword("->"),
+                    alloc.reflow(" next, like:"),
+                ]),
+                alloc
+                    .parser_suggestion("module { echo, read } -> [menu]")
+                    .indent(4),
+            ]);
+
+            Report {
+                filename,
+                doc,
+                title: "WEIRD MODULE PARAMS".to_string(),
+                severity: Severity::RuntimeError,
+            }
+        }
+
+        EParams::Space(error, pos) => to_space_report(alloc, lines, filename, error, *pos),
+    }
+}
+
 fn to_exposes_report<'a>(
     alloc: &'a RocDocAllocator<'a>,
     lines: &LineInfo,