cgen: fix generated str method for enums that have C values (use ifs, instead of switch) (fix #25135) (#25157)

vlib/v/gen/c/auto_str_methods.v

@@ -378,6 +378,13 @@ fn (mut g Gen) gen_str_for_enum(info ast.Enum, styp string, str_fn_name string)
 		}
 		g.auto_str_funcs.writeln('\tret = string__plus(ret, _S("}"));')
 		g.auto_str_funcs.writeln('\treturn ret;')
+	} else if info.uses_exprs {
+		// The enum values could be C macros, expanded later to duplicate values, and we do not know if that is the case, so we can not use a switch here.
+		// Instead we generate multiple if statements, which is slower, but is guaranteed to work in the presence of duplicates.
+		for val in info.vals {
+			g.auto_str_funcs.writeln('\t\tif(it == ${s}__${val}){ return _S("${val}"); }')
+		}
+		g.auto_str_funcs.writeln('\t\treturn _S("unknown enum value");')
 	} else {
 		g.auto_str_funcs.writeln('\tswitch(it) {')
 		// Only use the first multi value on the lookup

vlib/v/tests/project_with_c_code_2/main2_test.v

@@ -6,3 +6,16 @@ fn test_using_c_code_in_the_same_module_works() {
 	modc.destroy_vtype(x)
 	assert true
 }
+
+fn test_enum_with_dups_on_the_cside() {
+	for e in [modc.MyEnum.unknown, .name1, .name2, .name3, .name4, .name5, .name6, .common_name1,
+		.common_name2, .common_name3] {
+		println('>>> e: ${e} | int(e): ${int(e)}')
+	}
+	assert modc.MyEnum.name1 == modc.MyEnum.common_name1
+	assert modc.MyEnum.name2 == modc.MyEnum.common_name2
+	assert modc.MyEnum.name3 == modc.MyEnum.common_name3
+	assert modc.MyEnum.name4 != modc.MyEnum.common_name1
+	assert modc.MyEnum.name5 != modc.MyEnum.common_name2
+	assert modc.MyEnum.name6 != modc.MyEnum.common_name3
+}

vlib/v/tests/project_with_c_code_2/modc/header.h

@@ -15,5 +15,29 @@ void handle_array2(void *p, int n);
 void destroy_atype(void *p);
 
 
+// The following emulates the structure of the SDL3 header SDL_pixels.h, and the enum SDL_PixelFormat.
+// See also https://github.com/vlang/v/issues/25135 .
+#define ABC 1
+#define XYZ 1
+
+typedef enum EnumWithDuplicates {
+    UNKNOWN = 0,
+    NAME1 = 0x1u,
+    NAME2 = 0x2u,
+    NAME3 = 0x3u,
+    NAME4 = 0x4u,
+    NAME5 = 0x5u,
+    NAME6 = 0x6u,
+    #if ABC == XYZ
+	    COMMON_NAME1 = NAME1,
+	    COMMON_NAME2 = NAME2,
+	    COMMON_NAME3 = NAME3
+    #else
+	    COMMON_NAME1 = NAME4,
+	    COMMON_NAME2 = NAME5,
+	    COMMON_NAME3 = NAME6
+    #endif
+} EnumWithDuplicates;
+
 #endif
 

vlib/v/tests/project_with_c_code_2/modc/wrapper.c.v

@@ -51,3 +51,16 @@ pub fn call_with_array_param(arr []Vtype) {
 pub fn destroy_vtype(t Vtype) {
 	C.destroy_atype(t.p)
 }
+
+pub enum MyEnum {
+	unknown      = C.UNKNOWN
+	name1        = C.NAME1
+	name2        = C.NAME2
+	name3        = C.NAME3
+	name4        = C.NAME4
+	name5        = C.NAME5
+	name6        = C.NAME6
+	common_name1 = C.COMMON_NAME1
+	common_name2 = C.COMMON_NAME2
+	common_name3 = C.COMMON_NAME3
+}