Sema: rewrite peer type resolution

The existing logic for peer type resolution was quite convoluted and
buggy. This rewrite makes it much more resilient, readable, and
extensible. The algorithm works by first iterating over the types to
select a "strategy", then applying that strategy, possibly applying peer
resolution recursively.

Several new tests have been added to cover cases which the old logic did
not correctly handle.

Resolves: #15138
Resolves: #15644
Resolves: #15693
Resolves: #15709
Resolves: #15752

3 files changed, 61 insertions, 37 deletions

diff --git a/test/cases/compile_errors/compare_optional_to_non-optional_with_invalid_types.zig b/test/cases/compile_errors/compare_optional_to_non-optional_with_invalid_types.zig
deleted file mode 100644
index 0339ac034e..0000000000
--- a/test/cases/compile_errors/compare_optional_to_non-optional_with_invalid_types.zig
+++ /dev/null
@@ -1,37 +0,0 @@
-export fn inconsistentChildType() void {
-    var x: ?i32 = undefined;
-    const y: comptime_int = 10;
-    _ = (x == y);
-}
-export fn optionalToOptional() void {
-    var x: ?i32 = undefined;
-    var y: ?i32 = undefined;
-    _ = (x == y);
-}
-export fn optionalVector() void {
-    var x: ?@Vector(10, i32) = undefined;
-    var y: @Vector(10, i32) = undefined;
-    _ = (x == y);
-}
-export fn optionalVector2() void {
-    var x: ?@Vector(10, i32) = undefined;
-    var y: @Vector(11, i32) = undefined;
-    _ = (x == y);
-}
-export fn invalidChildType() void {
-    var x: ?[3]i32 = undefined;
-    var y: [3]i32 = undefined;
-    _ = (x == y);
-}
-
-// error
-// backend=llvm
-// target=native
-//
-// :4:12: error: incompatible types: '?i32' and 'comptime_int'
-// :4:10: note: type '?i32' here
-// :4:15: note: type 'comptime_int' here
-// :19:12: error: incompatible types: '?@Vector(10, i32)' and '@Vector(11, i32)'
-// :19:10: note: type '?@Vector(10, i32)' here
-// :19:15: note: type '@Vector(11, i32)' here
-// :24:12: error: operator == not allowed for type '?[3]i32'
diff --git a/test/cases/compile_errors/compare_optional_to_non_optional_with_incomparable_type.zig b/test/cases/compile_errors/compare_optional_to_non_optional_with_incomparable_type.zig
new file mode 100644
index 0000000000..653b7ffcfb
--- /dev/null
+++ b/test/cases/compile_errors/compare_optional_to_non_optional_with_incomparable_type.zig
@@ -0,0 +1,11 @@
+export fn entry() void {
+    var x: ?[3]i32 = undefined;
+    var y: [3]i32 = undefined;
+    _ = (x == y);
+}
+
+// error
+// backend=llvm
+// target=native
+//
+// :4:12: error: operator == not allowed for type '?[3]i32'
diff --git a/test/cases/compile_errors/invalid_peer_type_resolution.zig b/test/cases/compile_errors/invalid_peer_type_resolution.zig
new file mode 100644
index 0000000000..d82986a60a
--- /dev/null
+++ b/test/cases/compile_errors/invalid_peer_type_resolution.zig
@@ -0,0 +1,50 @@
+export fn optionalVector() void {
+    var x: ?@Vector(10, i32) = undefined;
+    var y: @Vector(11, i32) = undefined;
+    _ = @TypeOf(x, y);
+}
+export fn badTupleField() void {
+    var x = .{ @as(u8, 0), @as(u32, 1) };
+    var y = .{ @as(u8, 1), "hello" };
+    _ = @TypeOf(x, y);
+}
+export fn badNestedField() void {
+    const x = .{ .foo = "hi", .bar = .{ 0, 1 } };
+    const y = .{ .foo = "hello", .bar = .{ 2, "hi" } };
+    _ = @TypeOf(x, y);
+}
+export fn incompatiblePointers() void {
+    const x: []const u8 = "foo";
+    const y: [*:0]const u8 = "bar";
+    _ = @TypeOf(x, y);
+}
+export fn incompatiblePointers4() void {
+    const a: *const [5]u8 = "hello";
+    const b: *const [3:0]u8 = "foo";
+    const c: []const u8 = "baz"; // The conflict must be reported against this element!
+    const d: [*]const u8 = "bar";
+    _ = @TypeOf(a, b, c, d);
+}
+
+// error
+// backend=llvm
+// target=native
+//
+// :4:9: error: incompatible types: '?@Vector(10, i32)' and '@Vector(11, i32)'
+// :4:17: note: type '?@Vector(10, i32)' here
+// :4:20: note: type '@Vector(11, i32)' here
+// :9:9: error: struct field '1' has conflicting types
+// :9:9: note: incompatible types: 'u32' and '*const [5:0]u8'
+// :9:17: note: type 'u32' here
+// :9:20: note: type '*const [5:0]u8' here
+// :14:9: error: struct field 'bar' has conflicting types
+// :14:9: note: struct field '1' has conflicting types
+// :14:9: note: incompatible types: 'comptime_int' and '*const [2:0]u8'
+// :14:17: note: type 'comptime_int' here
+// :14:20: note: type '*const [2:0]u8' here
+// :19:9: error: incompatible types: '[]const u8' and '[*:0]const u8'
+// :19:17: note: type '[]const u8' here
+// :19:20: note: type '[*:0]const u8' here
+// :26:9: error: incompatible types: '[]const u8' and '[*]const u8'
+// :26:23: note: type '[]const u8' here
+// :26:26: note: type '[*]const u8' here