parser: fix C struct nested anon struct language

vlib/builtin/cfns.c.v

@@ -552,8 +552,23 @@ fn C.sysconf(name int) int
 // C.SYSTEM_INFO contains information about the current computer system. This includes the architecture and type of the processor, the number of processors in the system, the page size, and other such information.
 @[typedef]
 pub struct C.SYSTEM_INFO {
-	dwNumberOfProcessors u32
-	dwPageSize           u32
+	// DUMMYUNIONNAME              union {
+	//	dwOemId         u32
+	//	DUMMYSTRUCTNAME struct {
+	//	pub:
+	//		wProcessorArchitecture u16
+	//		wReserved              u16
+	//	}
+	//}
+	dwPageSize                  u32
+	lpMinimumApplicationAddress voidptr
+	lpMaximumApplicationAddress voidptr
+	dwActiveProcessorMask       &u32 = unsafe { nil }
+	dwNumberOfProcessors        u32
+	dwProcessorType             u32
+	dwAllocationGranularity     u32
+	wProcessorLevel             u16
+	wProcessorRevision          u16
 }
 
 fn C.GetSystemInfo(&C.SYSTEM_INFO)

vlib/v/ast/types.v

@@ -1091,7 +1091,8 @@ pub fn (t &TypeSymbol) is_array_fixed() bool {
 
 pub fn (t &TypeSymbol) is_c_struct() bool {
 	if t.info is Struct {
-		return t.language == .c
+		// `C___VAnonStruct` need special handle, it need to create a new struct
+		return t.language == .c && !t.info.is_anon
 	} else if t.info is Alias {
 		return global_table.final_sym(t.info.parent_type).is_c_struct()
 	}

vlib/v/gen/c/auto_str_methods.v

@@ -1188,7 +1188,11 @@ fn struct_auto_str_func(sym &ast.TypeSymbol, lang ast.Language, _field_type ast.
 		if sym.kind == .struct {
 			if sym.info is ast.Struct && sym.info.is_anon && !_field_type.has_flag(.option)
 				&& !_field_type.has_flag(.shared_f) {
-				typed_obj := '*(${sym.cname}*)&(${obj})'
+				typed_obj := if lang == .c {
+					'(${sym.cname}*)&(${obj})'
+				} else {
+					'*(${sym.cname}*)&(${obj})'
+				}
 				return '${fn_name}(${typed_obj})', true
 			}
 		}

vlib/v/gen/c/cgen.v

@@ -1723,7 +1723,9 @@ fn (mut g Gen) cc_type(typ ast.Type, is_prefix_struct bool) string {
 		styp = styp[3..]
 		if sym.kind == .struct {
 			info := sym.info as ast.Struct
-			if !info.is_typedef {
+			if info.is_anon {
+				styp = 'C__' + styp
+			} else if !info.is_typedef {
 				styp = 'struct ${styp}'
 			}
 		}
@@ -6925,7 +6927,11 @@ fn (mut g Gen) write_types(symbols []&ast.TypeSymbol) {
 	mut struct_names := map[string]bool{}
 	for sym in symbols {
 		if sym.name.starts_with('C.') {
-			continue
+			if sym.info is ast.Struct && sym.info.is_anon {
+				// For `C___VAnonStruct`, we need to create a new struct to make auto_str work.
+			} else {
+				continue
+			}
 		}
 		if sym.kind == .none && (!g.pref.skip_unused || g.table.used_features.used_none > 0) {
 			g.type_definitions.writeln('struct none {')

vlib/v/parser/parser.v

@@ -30,6 +30,7 @@ mut:
 	peek_tok                 token.Token
 	language                 ast.Language
 	fn_language              ast.Language // .c for `fn C.abcd()` declarations
+	struct_language          ast.Language // for `struct C.abcd{ embedded struct/union }` declarations
 	expr_level               int          // prevent too deep recursions for pathological programs
 	inside_vlib_file         bool         // true for all vlib/ files
 	inside_test_file         bool         // when inside _test.v or _test.vv file

vlib/v/parser/struct.v

@@ -31,8 +31,18 @@ fn (mut p Parser) struct_decl(is_anon bool) ast.StructDecl {
 	} else {
 		p.check(.key_union)
 	}
-	language := p.parse_language()
+	mut language := p.parse_language()
 	name_pos := p.tok.pos()
+	if p.inside_struct_field_decl && language == .v {
+		// anon struct/union language should keep the same language of outside
+		language = p.struct_language
+	} else {
+		old_struct_language := p.struct_language
+		p.struct_language = language
+		defer(fn) {
+			p.struct_language = old_struct_language
+		}
+	}
 	p.check_for_impure_v(language, name_pos)
 	if p.disallow_declarations_in_script_mode() {
 		return ast.StructDecl{}

vlib/v/tests/c_structs/cstruct_nested_anon_test.c.v

@@ -0,0 +1,23 @@
+module main
+
+#insert "@VMODROOT/deep.h"
+
+struct C.DeepStruct {
+	A1 int
+	S1 struct {
+		A2 int
+		S2 struct {
+			A3 int
+			S3 struct {
+				A4 int
+			}
+		}
+	}
+}
+
+fn test_cstruct_nested_anon() {
+	x := C.DeepStruct{}
+	y := C.DeepStruct{}
+	dump(x)
+	assert x == y
+}

vlib/v/tests/c_structs/deep.h

@@ -0,0 +1,16 @@
+#ifndef __DEEP_H__
+#define __DEEP_H__
+
+struct DeepStruct{
+	int A1;
+	struct {
+		int A2;
+		struct {
+		       int A3;
+		       struct {
+				int A4;
+		       } S3;
+                } S2;
+        } S1;
+};
+#endif