Change union layout to store type info rather than an integer; ternary expression for types with constant condition

core/_preload.odin

@@ -82,7 +82,8 @@ TypeInfo :: struct #ordered {
 	Struct       :: Record;
 	RawUnion     :: Record;
 	Union :: struct #ordered {
-		variants: []^TypeInfo;
+		variants:   []^TypeInfo;
+		tag_offset: int;
 	};
 	Enum :: struct #ordered {
 		base:   ^TypeInfo;

core/c.odin

@@ -0,0 +1,41 @@
+CHAR_BIT :: 8;
+
+c_bool           :: bool;
+
+c_char           :: u8;
+
+c_schar          :: i8;
+c_uchar          :: i8;
+
+c_short          :: i16;
+c_ushort         :: i16;
+
+c_int            :: i32;
+c_uint           :: u32;
+
+c_long  :: ODIN_OS == "windows" ?
+	i32 :
+	(size_of(int) == 4) ?
+		i32 :
+		i64;
+
+c_ulong :: ODIN_OS == "windows" ?
+	u32 :
+	(size_of(int) == 4) ?
+		u32 :
+		u64;
+
+c_longlong       :: i64;
+c_ulonglong      :: u64;
+
+c_float          :: f32;
+c_double         :: f64;
+
+c_complex_float  :: complex64;
+c_complex_double :: complex128;
+
+c_size_t         :: uint;
+c_ssize_t        :: int;
+c_ptrdiff_t      :: int;
+c_uintptr_t      :: uint;
+c_intptr_t       :: int;

core/fmt.odin

@@ -866,7 +866,15 @@ fmt_value :: proc(fi: ^FmtInfo, v: any, verb: rune) {
 		}
 
 	case Union:
-		write_string(fi.buf, "(union)");
+		data := cast(^u8)v.data;
+		tipp := cast(^^TypeInfo)(data + info.tag_offset);
+		if data == nil || tipp == nil {
+			write_string(fi.buf, "(union)");
+		} else {
+			ti := tipp^;
+			fmt_arg(fi, any{data, ti}, verb);
+		}
+
 
 	case RawUnion:
 		write_string(fi.buf, "(raw_union)");