Report import lowercase alias

crates/compiler/load/tests/test_reporting.rs

@@ -4987,6 +4987,25 @@ mod test_reporting {
     "###
     );
 
+    test_report!(
+        lowercase_import_alias,
+        indoc!(
+            r"
+            import svg.Path as path
+            "
+        ),
+        @r###"
+    ── LOWERCASE ALIAS in tmp/lowercase_import_alias/Test.roc ──────────────────────
+
+    This import is using a lowercase alias:
+
+    4│      import svg.Path as path
+                               ^^^^
+
+    Module names and aliases must start with an uppercase letter.
+    "###
+    );
+
     test_report!(
         ingested_file_import_ann_syntax_err,
         indoc!(

crates/compiler/parse/src/expr.rs

@@ -9,8 +9,7 @@ use crate::blankspace::{
     space0_before_optional_after, space0_e, spaces, spaces_around, spaces_before,
 };
 use crate::ident::{
-    integer_ident, lowercase_ident, parse_ident, unqualified_ident, uppercase_ident, Accessor,
-    Ident, Suffix,
+    integer_ident, lowercase_ident, parse_ident, unqualified_ident, Accessor, Ident, Suffix,
 };
 use crate::module::module_name_help;
 use crate::parser::{
@@ -997,10 +996,20 @@ fn import_as<'a>(
             EImport::IndentAs,
             EImport::IndentAlias
         ),
-        item: loc!(map!(
-            specialize_err(|_, pos| EImport::Alias(pos), uppercase_ident()),
-            ImportAlias::new
-        ))
+        item: then(
+            specialize_err(|_, pos| EImport::Alias(pos), loc!(unqualified_ident())),
+            |_arena, state, _progress, loc_ident| {
+                match loc_ident.value.chars().next() {
+                    Some(first) if first.is_uppercase() => Ok((
+                        MadeProgress,
+                        loc_ident.map(|ident| ImportAlias::new(ident)),
+                        state,
+                    )),
+                    Some(_) => Err((MadeProgress, EImport::LowercaseAlias(loc_ident.region))),
+                    None => Err((MadeProgress, EImport::Alias(state.pos()))),
+                }
+            }
+        )
     })
 }
 

crates/compiler/parse/src/parser.rs

@@ -534,6 +534,7 @@ pub enum EImport<'a> {
     As(Position),
     IndentAlias(Position),
     Alias(Position),
+    LowercaseAlias(Region),
     IndentExposing(Position),
     Exposing(Position),
     ExposingListStart(Position),

crates/reporting/src/error/parse.rs

@@ -1514,7 +1514,23 @@ fn to_import_report<'a>(
                 alloc.reflow(" keyword, so I was expecting to see an alias next."),
             ]),
         ),
+        LowercaseAlias(region) => {
+            let surroundings = Region::new(start, region.end());
+            let region = lines.convert_region(*region);
 
+            let doc = alloc.stack([
+                alloc.reflow(r"This import is using a lowercase alias:"),
+                alloc.region_with_subregion(lines.convert_region(surroundings), region),
+                alloc.reflow(r"Module names and aliases must start with an uppercase letter."),
+            ]);
+
+            Report {
+                filename,
+                doc,
+                title: "LOWERCASE ALIAS".to_string(),
+                severity: Severity::RuntimeError,
+            }
+        }
         Annotation(problem, pos) => to_type_report(alloc, lines, filename, problem, *pos),
         Space(problem, pos) => to_space_report(alloc, lines, filename, problem, *pos),
         ExposingListStart(_) => todo!(),