AstGen: reset anon_name_strategy for sub expressions

Closes  #12910

src/AstGen.zig

@@ -577,6 +577,12 @@ fn expr(gz: *GenZir, scope: *Scope, rl: ResultLoc, node: Ast.Node.Index) InnerEr
     const node_datas = tree.nodes.items(.data);
     const node_tags = tree.nodes.items(.tag);
 
+    const prev_anon_name_strategy = gz.anon_name_strategy;
+    defer gz.anon_name_strategy = prev_anon_name_strategy;
+    if (!nodeUsesAnonNameStrategy(tree, node)) {
+        gz.anon_name_strategy = .anon;
+    }
+
     switch (node_tags[node]) {
         .root => unreachable, // Top-level declaration.
         .@"usingnamespace" => unreachable, // Top-level declaration.
@@ -9344,6 +9350,32 @@ fn nodeImpliesComptimeOnly(tree: *const Ast, start_node: Ast.Node.Index) bool {
     }
 }
 
+/// Returns `true` if the node uses `gz.anon_name_strategy`.
+fn nodeUsesAnonNameStrategy(tree: *const Ast, node: Ast.Node.Index) bool {
+    const node_tags = tree.nodes.items(.tag);
+    switch (node_tags[node]) {
+        .container_decl,
+        .container_decl_trailing,
+        .container_decl_two,
+        .container_decl_two_trailing,
+        .container_decl_arg,
+        .container_decl_arg_trailing,
+        .tagged_union,
+        .tagged_union_trailing,
+        .tagged_union_two,
+        .tagged_union_two_trailing,
+        .tagged_union_enum_tag,
+        .tagged_union_enum_tag_trailing,
+        => return true,
+        .builtin_call_two, .builtin_call_two_comma, .builtin_call, .builtin_call_comma => {
+            const builtin_token = tree.nodes.items(.main_token)[node];
+            const builtin_name = tree.tokenSlice(builtin_token);
+            return std.mem.eql(u8, builtin_name, "@Type");
+        },
+        else => return false,
+    }
+}
+
 /// Applies `rl` semantics to `result`. Expressions which do not do their own handling of
 /// result locations must call this function on their result.
 /// As an example, if the `ResultLoc` is `ptr`, it will write the result to the pointer.

test/behavior/typename.zig

@@ -246,3 +246,28 @@ test "comptime parameters not converted to anytype in function type" {
     const T = fn (fn (type) void, void) void;
     try expectEqualStrings("fn(comptime fn(comptime type) void, void) void", @typeName(T));
 }
+
+test "anon name strategy used in sub expression" {
+    if (builtin.zig_backend == .stage1) {
+        // stage1 uses line/column for the names but we're moving away from that for
+        // incremental compilation purposes.
+        return error.SkipZigTest;
+    }
+
+    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
+    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
+
+    const S = struct {
+        fn getTheName() []const u8 {
+            return struct {
+                const name = @typeName(@This());
+            }.name;
+        }
+    };
+    try expectEqualStringsIgnoreDigits(
+        "behavior.typename.test.anon name strategy used in sub expression.S.getTheName__struct_0",
+        S.getTheName(),
+    );
+}