More error message improvements

src/check/Check.zig

@@ -155,6 +155,23 @@ pub fn unify(self: *Self, a: Var, b: Var) std.mem.Allocator.Error!unifier.Result
     );
 }
 
+pub fn unifyWithAnnotation(self: *Self, a: Var, b: Var) std.mem.Allocator.Error!unifier.Result {
+    const trace = tracy.trace(@src());
+    defer trace.end();
+
+    return try unifier.unifyWithContext(
+        self.cir,
+        self.types,
+        &self.problems,
+        &self.snapshots,
+        &self.unify_scratch,
+        &self.occurs_scratch,
+        a,
+        b,
+        true, // from_annotation = true
+    );
+}
+
 // instantiate //
 
 const InstantiateRegionBehavior = union(enum) {
@@ -406,7 +423,7 @@ fn checkDef(self: *Self, def_idx: CIR.Def.Idx) std.mem.Allocator.Error!void {
             _ = try self.checkExpr(def.expr);
 
             // Unify the expression with its annotation
-            _ = try self.unify(expr_var, anno_var);
+            _ = try self.unifyWithAnnotation(expr_var, anno_var);
         }
     } else {
         // Check the expr
@@ -1469,7 +1486,7 @@ fn checkLambdaWithAnno(
 
                     // Unify against the annotation
                     const pattern_var = ModuleEnv.varFrom(pattern_idx);
-                    _ = try self.unify(pattern_var, expected_arg);
+                    _ = try self.unifyWithAnnotation(pattern_var, expected_arg);
                 }
             }
         }
@@ -1493,12 +1510,12 @@ fn checkLambdaWithAnno(
 
     // STEP 4: Validate the function body against the annotation return type
     if (mb_expected_func) |func| {
-        _ = try self.unify(return_var, func.ret);
+        _ = try self.unifyWithAnnotation(return_var, func.ret);
     }
 
     // STEP 5: Validate the entire function against the annotation
     if (mb_expected_var) |expected_var| {
-        _ = try self.unify(fn_var, expected_var);
+        _ = try self.unifyWithAnnotation(fn_var, expected_var);
     }
 
     return is_effectful;

src/check/problem.zig

@@ -84,6 +84,8 @@ pub const TypePair = struct {
     expected_snapshot: SnapshotContentIdx,
     actual_var: Var,
     actual_snapshot: SnapshotContentIdx,
+    /// True if the expected type comes from a type annotation
+    from_annotation: bool = false,
 };
 
 /// More specific details about a particular type mismatch.
@@ -335,7 +337,11 @@ pub const ReportBuilder = struct {
         );
         try report.document.addLineBreak();
 
-        try report.document.addText("The type annotation says it should have the type:");
+        if (types.from_annotation) {
+            try report.document.addText("The type annotation says it should have the type:");
+        } else {
+            try report.document.addText("It is of type:");
+        }
         try report.document.addLineBreak();
         try report.document.addText("    ");
         try report.document.addAnnotated(owned_actual, .type_variable);

src/check/unify.zig

@@ -114,13 +114,8 @@ pub const Result = union(enum) {
     }
 };
 
-/// Unify two type variables
-///
-/// This function
-/// * Resolves type variables & compresses paths
-/// * Compares variable contents for equality
-/// * Merges unified variables so 1 is "root" and the other is "redirect"
-pub fn unify(
+/// Unify two type variables with context about whether this is from an annotation
+pub fn unifyWithContext(
     module_env: *ModuleEnv,
     types: *types_mod.Store,
     problems: *problem_mod.Store,
@@ -129,6 +124,7 @@ pub fn unify(
     occurs_scratch: *occurs.Scratch,
     a: Var,
     b: Var,
+    from_annotation: bool,
 ) std.mem.Allocator.Error!Result {
     const trace = tracy.trace(@src());
     defer trace.end();
@@ -153,6 +149,7 @@ pub fn unify(
                             .expected_snapshot = expected_snapshot,
                             .actual_var = b,
                             .actual_snapshot = actual_snapshot,
+                            .from_annotation = from_annotation,
                         },
                         .detail = null,
                     } };
@@ -287,6 +284,36 @@ pub fn unify(
     return .ok;
 }
 
+/// Unify two type variables
+///
+/// This function
+/// * Resolves type variables & compresses paths
+/// * Compares variable contents for equality
+/// * Merges unified variables so 1 is "root" and the other is "redirect"
+pub fn unify(
+    module_env: *ModuleEnv,
+    types: *types_mod.Store,
+    problems: *problem_mod.Store,
+    snapshots: *snapshot_mod.Store,
+    unify_scratch: *Scratch,
+    occurs_scratch: *occurs.Scratch,
+    a: Var,
+    b: Var,
+) std.mem.Allocator.Error!Result {
+    // Default to not from annotation for backward compatibility
+    return unifyWithContext(
+        module_env,
+        types,
+        problems,
+        snapshots,
+        unify_scratch,
+        occurs_scratch,
+        a,
+        b,
+        false, // from_annotation = false by default
+    );
+}
+
 /// A temporary unification context used to unify two type variables within a `Store`.
 ///
 /// `Unifier` is created per unification call and:

test/snapshots/expr/not_tag.md

@@ -18,7 +18,7 @@ This expression is used in an unexpected way:
 ```
 ^^^^^^^
 
-The type annotation says it should have the type:
+It is of type:
     _Bool_
 
 But you are trying to use it as:

test/snapshots/fuzz_crash/fuzz_crash_019.md

@@ -875,7 +875,7 @@ This expression is used in an unexpected way:
 	)crash ke"Unr!" #)
 ```
 
-The type annotation says it should have the type:
+It is of type:
     __arg -> _ret_
 
 But you are trying to use it as:

test/snapshots/fuzz_crash/fuzz_crash_023.md

@@ -961,7 +961,7 @@ This expression is used in an unexpected way:
 	)
 ```
 
-The type annotation says it should have the type:
+It is of type:
     __arg -> _ret_
 
 But you are trying to use it as:

test/snapshots/fuzz_crash/fuzz_crash_027.md

@@ -912,7 +912,7 @@ This expression is used in an unexpected way:
 	)
 ```
 
-The type annotation says it should have the type:
+It is of type:
     __arg -> _ret_
 
 But you are trying to use it as:

test/snapshots/lambda_annotation_mismatch_error.md

@@ -26,7 +26,7 @@ string_function = |x| x + 42
 ```
                       ^
 
-The type annotation says it should have the type:
+It is of type:
     _Str_
 
 But you are trying to use it as:

test/snapshots/lambda_currying_constraint.md

@@ -86,7 +86,7 @@ makeAdder = |x| |y| x + y
 ```
                     ^
 
-The type annotation says it should have the type:
+It is of type:
     _a_
 
 But you are trying to use it as:

test/snapshots/simple_lambda_constraint_success.md

@@ -26,7 +26,7 @@ addTwoF64 = |x| x + 2.0
 ```
                 ^
 
-The type annotation says it should have the type:
+It is of type:
     _F64_
 
 But you are trying to use it as:

test/snapshots/syntax_grab_bag.md

@@ -897,7 +897,7 @@ This expression is used in an unexpected way:
 	)
 ```
 
-The type annotation says it should have the type:
+It is of type:
     __arg -> _ret_
 
 But you are trying to use it as:

test/snapshots/test_exact_pattern_crash.md

@@ -56,7 +56,7 @@ This expression is used in an unexpected way:
 ```
          ^^^^^^^^
 
-The type annotation says it should have the type:
+It is of type:
     _Num(_size), Num(_size2), Num(_size3) -> Num(_size4), Num(_size5) -> Num(_size6) -> _ret_
 
 But you are trying to use it as:

test/snapshots/test_instantiation_arity_mismatch.md

@@ -23,7 +23,7 @@ This expression is used in an unexpected way:
 ```
     ^^^^^^^^^^^^^^
 
-The type annotation says it should have the type:
+It is of type:
     _Num(_size), Num(_size2) -> _ret_
 
 But you are trying to use it as:

test/snapshots/test_tuple_instantiation_crash.md

@@ -26,7 +26,7 @@ main = swap(1, 2)
 ```
        ^^^^
 
-The type annotation says it should have the type:
+It is of type:
     _Num(_size), Num(_size2) -> _ret_
 
 But you are trying to use it as:

test/snapshots/type_alias_parameterized.md

@@ -25,7 +25,7 @@ main! = |_| swapPair(1, 2)
 ```
             ^^^^^^^^
 
-The type annotation says it should have the type:
+It is of type:
     _Num(_size), Num(_size2) -> _ret_
 
 But you are trying to use it as:

test/snapshots/type_app_with_vars.md

@@ -23,7 +23,7 @@ main! = |_| mapList([1,2,3,4,5])
 ```
             ^^^^^^^
 
-The type annotation says it should have the type:
+It is of type:
     _List(Num(_size)) -> _ret_
 
 But you are trying to use it as: