"parameter type declared here" should additionally be provided for unions

[andrewrk]

Zig Version

0.14.0-dev.2370+5c6b25d9b

Steps to Reproduce and Observed Output

In this example we get desired output for enums:

const A = struct {
    x: Index,

    const Index = enum(u32) { none = 0, _ };

    fn init(x: Index) A {
        return .{ .x = x };
    }
};

const B = struct {
    x: Index,

    const Index = enum(u32) { none = 0, _ };

    fn init(x: Index) B {
        return .{ .x = x };
    }
};

test "example" {
    var a = mystery();
    a.field = .init(A.Index.none);
}

// If the below source is in a different file, one must rely on the compile
// error to tell which function is being called.

const C = struct {
    field: B,
};

fn mystery() C {
    return undefined;
}

test.zig:23:28: error: expected type 'test.B.Index', found 'test.A.Index'
    a.field = .init(A.Index.none);
                    ~~~~~~~^~~~~
test.zig:4:19: note: enum declared here
    const Index = enum(u32) { none = 0, _ };
                  ^~~~~~~~~~~~~~~~~~~~~~~~~
test.zig:14:19: note: enum declared here
    const Index = enum(u32) { none = 0, _ };
                  ^~~~~~~~~~~~~~~~~~~~~~~~~
test.zig:16:16: note: parameter type declared here
    fn init(x: Index) B {
               ^~~~~

✔️ Good

However, if you change both enums to unions, then we no longer have a note that tells which function is being called:

-    const Index = enum(u32) { none = 0, _ };
+    const Index = union(enum(u32)) { none = 0, _ };

test.zig:23:28: error: expected type '@typeInfo(test.B.Index).@"union".tag_type.?', found '@typeInfo(test.A.Index).@"union".tag_type.?'
    a.field = .init(A.Index.none);
                    ~~~~~~~^~~~~
test.zig:4:19: note: enum declared here
    const Index = union(enum(u32)) { none = 0, _ };
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.zig:14:19: note: enum declared here
    const Index = union(enum(u32)) { none = 0, _ };
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

❌ Missing function definition note

Expected Output

The additional error note that mentions the function definition source location:

test.zig:16:16: note: parameter type declared here
    fn init(x: Index) B {
               ^~~~~

[mlugg]

This is because Sema.coerceExtra in this case calls coerceEnumToUnion, which drops the opts.param_src data, which is responsible for adding the parameter type declared here note. We either need to forward this data to that function, or add this note differently by catching error.AnalysisFail somewhere rather than including it in opts.