Reintroduce exhaustiveness checking for use (#3880)

CHANGELOG.md

@@ -10,10 +10,19 @@
 
 ### Formatter
 
+### Bug fix
+
+## v1.6.2 - 2024-11-23
+
 ### Bug fixed
 
+- Fixed a bug where patterns in `use` expressions would not be checked to ensure that
+  they were exhaustive.
+  ([Surya Rose](https://github.com/GearsDatapacks))
+
 ## v1.6.1 - 2024-11-19
 
-### Bug fixed
+### Bug fix
 
 - Fixed a bug where `gleam update` would fail to update versions.
+  ([Jason Sipula](https://github.com/SnakeDoc))

compiler-core/src/type_/expression.rs

@@ -1353,10 +1353,8 @@ impl<'a, 'b> ExprTyper<'a, 'b> {
         // Do not perform exhaustiveness checking if user explicitly used `let assert ... = ...`.
         let exhaustiveness_check = self.check_let_exhaustiveness(location, value.type_(), &pattern);
         match (kind, exhaustiveness_check) {
-            // Generated assignments should be checked before they are generated
-            (AssignmentKind::Generated, _) => {}
-            (AssignmentKind::Let, Ok(_)) => {}
-            (AssignmentKind::Let, Err(e)) => {
+            (AssignmentKind::Let | AssignmentKind::Generated, Ok(_)) => {}
+            (AssignmentKind::Let | AssignmentKind::Generated, Err(e)) => {
                 self.problems.error(e);
             }
             (AssignmentKind::Assert { location }, Ok(_)) => self

compiler-core/src/type_/tests/errors.rs

@@ -2639,3 +2639,14 @@ pub fn main() {
 "
     );
 }
+
+#[test]
+// https://github.com/gleam-lang/gleam/issues/3879
+fn inexhaustive_use_reports_error() {
+    assert_error!(
+        r#"
+use [1, 2, 3] <- todo
+todo
+"#
+    );
+}

compiler-core/src/type_/tests/snapshots/gleam_core__type___tests__errors__inexhaustive_use_reports_error.snap

@@ -0,0 +1,29 @@
+---
+source: compiler-core/src/type_/tests/errors.rs
+expression: "\nuse [1, 2, 3] <- todo\ntodo\n"
+---
+----- SOURCE CODE
+
+use [1, 2, 3] <- todo
+todo
+
+
+----- ERROR
+error: Inexhaustive pattern
+  ┌─ /src/one/two.gleam:2:5
+  │
+2 │ use [1, 2, 3] <- todo
+  │     ^^^^^^^^^
+
+This assignment uses a pattern that does not match all possible values. If
+one of the other values is used then the assignment will crash.
+
+The missing patterns are:
+
+    []
+    [_, _, _, _, ..]
+    [_, _, _]
+    [_, _]
+    [_]
+
+Hint: Use a more general pattern or use `let assert` instead.