add is_tuple field to struct typeinfo

part of #4335

lib/std/builtin.zig

@@ -246,6 +246,7 @@ pub const TypeInfo = union(enum) {
         layout: ContainerLayout,
         fields: []const StructField,
         decls: []const Declaration,
+        is_tuple: bool,
     };
 
     /// This data structure is used by the Zig language code generation and

lib/std/mem.zig

@@ -709,8 +709,7 @@ pub fn zeroInit(comptime T: type, init: anytype) T {
                 .Struct => |init_info| {
                     var value = std.mem.zeroes(T);
 
-                    // typeInfo won't tell us if this is a tuple
-                    if (comptime eql(u8, init_info.fields[0].name, "0")) {
+                    if (init_info.is_tuple) {
                         inline for (init_info.fields) |field, i| {
                             @field(value, struct_info.fields[i].name) = @field(init, field.name);
                         }
@@ -785,7 +784,7 @@ test "zeroInit" {
         a: u8,
     };
 
-    const c = zeroInit(Color, .{255, 255});
+    const c = zeroInit(Color, .{ 255, 255 });
     testing.expectEqual(Color{
         .r = 255,
         .g = 255,

src/ir.cpp

@@ -25546,7 +25546,7 @@ static Error ir_make_type_info_value(IrAnalyze *ira, IrInst* source_instr, ZigTy
                 result->special = ConstValSpecialStatic;
                 result->type = ir_type_info_get_type(ira, "Struct", nullptr);
 
-                ZigValue **fields = alloc_const_vals_ptrs(ira->codegen, 3);
+                ZigValue **fields = alloc_const_vals_ptrs(ira->codegen, 4);
                 result->data.x_struct.fields = fields;
 
                 // layout: ContainerLayout
@@ -25627,6 +25627,12 @@ static Error ir_make_type_info_value(IrAnalyze *ira, IrInst* source_instr, ZigTy
                     return err;
                 }
 
+                // is_tuple: bool
+                ensure_field_index(result->type, "is_tuple", 3);
+                fields[3]->special = ConstValSpecialStatic;
+                fields[3]->type = ira->codegen->builtin_types.entry_bool;
+                fields[3]->data.x_bool = is_tuple(type_entry);
+
                 break;
             }
         case ZigTypeIdFn:

test/stage1/behavior/type_info.zig

@@ -280,7 +280,7 @@ fn testFunction() void {
     expect(bound_fn_info.BoundFn.args[0].arg_type.? == *const TestStruct);
 }
 
-extern fn foo(a: usize, b: bool, args: ...) usize;
+extern fn foo(a: usize, b: bool, ...) usize;
 
 test "typeInfo with comptime parameter in struct fn def" {
     const S = struct {
@@ -425,3 +425,8 @@ test "Declarations are returned in declaration order" {
     expect(std.mem.eql(u8, d[3].name, "d"));
     expect(std.mem.eql(u8, d[4].name, "e"));
 }
+
+test "Struct.is_tuple" {
+    expect(@typeInfo(@TypeOf(.{0})).Struct.is_tuple);
+    expect(!@typeInfo(@TypeOf(.{ .a = 0 })).Struct.is_tuple);
+}