Do not implicitly convert enums to ordinal in formatting functions.

lib/std/core/string.c3

@@ -46,7 +46,7 @@ macro Char16[] @char16(String $string) @builtin
 
  @param [in] fmt : `The formatting string`
 *>
-fn ZString tformat_zstr(String fmt, args...)
+fn ZString tformat_zstr(String fmt, args...) @format(0)
 {
 	DString str = dstring::temp_with_capacity(fmt.len + args.len * 8);
 	str.appendf(fmt, ...args);
@@ -59,7 +59,7 @@ fn ZString tformat_zstr(String fmt, args...)
  @param [inout] allocator : `The allocator to use`
  @param [in] fmt : `The formatting string`
 *>
-fn String format(Allocator allocator, String fmt, args...) => @pool()
+fn String format(Allocator allocator, String fmt, args...) @format(1) => @pool()
 {
 	DString str = dstring::temp_with_capacity(fmt.len + args.len * 8);
 	str.appendf(fmt, ...args);
@@ -71,7 +71,7 @@ fn String format(Allocator allocator, String fmt, args...) => @pool()
 
  @param [in] fmt : `The formatting string`
 *>
-fn String tformat(String fmt, args...)
+fn String tformat(String fmt, args...) @format(0)
 {
 	DString str = dstring::temp_with_capacity(fmt.len + args.len * 8);
 	str.appendf(fmt, ...args);

lib/std/io/formatter.c3

@@ -339,7 +339,7 @@ macro usz? @wrap_bad(Formatter* f, #action)
         	case INTERNAL_BUFFER_EXCEEDED:
         		return f.first_err(err)?;
         	default:
-			err = f.first_err(INVALID_ARGUMENT);
+				err = f.first_err(INVALID_ARGUMENT);
         		f.out_substr("<INVALID>")!;
         		return err?;
 		}

lib/std/io/formatter_private.c3

@@ -43,7 +43,6 @@ fn uint128? int_from_any(any arg, bool *is_neg) @private
 			*is_neg = false;
 			return (uint128)(uptr)*(void**)arg.ptr;
 		case TypeKind.DISTINCT:
-		case TypeKind.ENUM:
 			return int_from_any(arg.as_inner(), is_neg);
 		default:
 			break;

lib/std/time/format.c3

@@ -45,18 +45,18 @@ fn String format(Allocator allocator, DateTimeFormat type, TzDateTime dt)
 			return string::format(allocator, "%s, %02d %s %d %02d:%02d:%02d %s", dt.weekday.abbrev, dt.day, dt.month.abbrev, dt.year, dt.hour, dt.min, dt.sec, temp_numeric_tzsuffix(dt.gmt_offset));
 		case RFC3339:
 			dt = dt.to_gmt_offset(0);
-			return string::format(allocator, "%04d-%02d-%02dT%02d:%02d:%02dZ", dt.year, dt.month + 1, dt.day, dt.hour, dt.min, dt.sec);
+			return string::format(allocator, "%04d-%02d-%02dT%02d:%02d:%02dZ", dt.year, dt.month.ordinal + 1, dt.day, dt.hour, dt.min, dt.sec);
 		case RFC3339Z:
-			return string::format(allocator, "%04d-%02d-%02dT%02d:%02d:%02d%s", dt.year, dt.month + 1, dt.day, dt.hour, dt.min, dt.sec, temp_numeric_tzsuffix_colon(dt.gmt_offset));
+			return string::format(allocator, "%04d-%02d-%02dT%02d:%02d:%02d%s", dt.year, dt.month.ordinal + 1, dt.day, dt.hour, dt.min, dt.sec, temp_numeric_tzsuffix_colon(dt.gmt_offset));
 		case RFC3339MS:
 			dt = dt.to_gmt_offset(0);
-			return string::format(allocator, "%04d-%02d-%02dT%02d:%02d:%02d.%dZ", dt.year, dt.month + 1, dt.day, dt.hour, dt.min, dt.sec, dt.usec);
+			return string::format(allocator, "%04d-%02d-%02dT%02d:%02d:%02d.%dZ", dt.year, dt.month.ordinal + 1, dt.day, dt.hour, dt.min, dt.sec, dt.usec);
 		case RFC3339ZMS:
-			return string::format(allocator, "%04d-%02d-%02dT%02d:%02d:%02d.%d%s", dt.year, dt.month + 1, dt.day, dt.hour, dt.min, dt.sec, dt.usec, temp_numeric_tzsuffix_colon(dt.gmt_offset));
+			return string::format(allocator, "%04d-%02d-%02dT%02d:%02d:%02d.%d%s", dt.year, dt.month.ordinal + 1, dt.day, dt.hour, dt.min, dt.sec, dt.usec, temp_numeric_tzsuffix_colon(dt.gmt_offset));
 		case DATETIME:
-			return string::format(allocator, "%04d-%02d-%02d %02d:%02d:%02d", dt.year, dt.month + 1, dt.day, dt.hour, dt.min, dt.sec);
+			return string::format(allocator, "%04d-%02d-%02d %02d:%02d:%02d", dt.year, dt.month.ordinal + 1, dt.day, dt.hour, dt.min, dt.sec);
 		case DATEONLY:
-			return string::format(allocator, "%04d-%02d-%02d", dt.year, dt.month + 1, dt.day);
+			return string::format(allocator, "%04d-%02d-%02d", dt.year, dt.month.ordinal + 1, dt.day);
 		case TIMEONLY:
 			return string::format(allocator, "%02d:%02d:%02d", dt.hour, dt.min, dt.sec);
 	}

releasenotes.md

@@ -44,6 +44,7 @@
 - `tmem` is now a variable.
 - Compile test and benchmark functions when invoking `--lsp` #2058.
 - Added `@format` attribute for compile time printf validation #2057.
+- Formatter no longer implicitly converts enums to ordinals.
 
 ### Fixes
 - Fix address sanitizer to work on MachO targets (e.g. MacOS).

src/compiler/sema_expr.c

@@ -1869,6 +1869,10 @@ CHECK_FORMAT:;
 				case 'G':
 					if (!type_is_number_or_bool(type))
 					{
+						if (type->type_kind == TYPE_ENUM)
+						{
+							RETURN_SEMA_ERROR(vaargs[idx], "An enum cannot directly be turned into a number. Use '.ordinal' to convert it to its value.", type_quoted_error_string(type));
+						}
 						RETURN_SEMA_ERROR(vaargs[idx], "Expected a number here, but was %s", type_quoted_error_string(type));
 					}
 					goto NEXT;

test/unit/stdlib/io/printf.c3

@@ -107,10 +107,10 @@ fn void printf_enum()
 	assert(s == "ENUMB", "got '%s'; want 'ENUMB'", s);
 	free(s);
 
-	s = string::format(mem, "%d", PrintfTest.ENUMA);
+	s = string::format(mem, "%d", PrintfTest.ENUMA.ordinal);
 	assert(s == "0", "got '%s'; want '0'", s);
 	free(s);
-	s = string::format(mem, "%d", PrintfTest.ENUMB);
+	s = string::format(mem, "%d", PrintfTest.ENUMB.ordinal);
 	assert(s == "1", "got '%s'; want '1'", s);
 	free(s);
 }