parser: error on recursive struct (#7964)

vlib/v/checker/checker.v

@@ -374,7 +374,7 @@ pub fn (mut c Checker) interface_decl(decl ast.InterfaceDecl) {
 	}
 }
 
-pub fn (mut c Checker) struct_decl(decl ast.StructDecl) {
+pub fn (mut c Checker) struct_decl(mut decl ast.StructDecl) {
 	if decl.language == .v && !c.is_builtin_mod {
 		c.check_valid_pascal_case(decl.name, 'struct name', decl.pos)
 	}
@@ -2962,7 +2962,7 @@ fn (mut c Checker) stmt(node ast.Stmt) {
 			c.sql_stmt(mut node)
 		}
 		ast.StructDecl {
-			c.struct_decl(node)
+			c.struct_decl(mut node)
 		}
 		ast.TypeDecl {
 			c.type_decl(node)

vlib/v/gen/cgen.v

@@ -4927,6 +4927,8 @@ fn (g &Gen) sort_structs(typesa []table.TypeSymbol) []table.TypeSymbol {
 	// sort graph
 	dep_graph_sorted := dep_graph.resolve()
 	if !dep_graph_sorted.acyclic {
+		// this should no longer be called since it's catched in the parser
+		// TODO: should it be removed?
 		verror('cgen.sort_structs(): the following structs form a dependency cycle:\n' + dep_graph_sorted.display_cycles() +
 			'\nyou can solve this by making one or both of the dependant struct fields references, eg: field &MyStruct' +
 			'\nif you feel this is an error, please create a new issue here: https://github.com/vlang/v/issues and tag @joe-conigliaro')

vlib/v/parser/struct.v

@@ -74,7 +74,16 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 		p.error_with_pos('struct names must have more than one character', name_pos)
 		return ast.StructDecl{}
 	}
-	// println('struct decl $name')
+	mut orig_name := name
+	if language == .c {
+		name = 'C.$name'
+		orig_name = name
+	} else if language == .js {
+		name = 'JS.$name'
+		orig_name = name
+	} else {
+		name = p.prepend_mod(name)
+	}
 	mut ast_fields := []ast.StructField{}
 	mut fields := []table.Field{}
 	mut embed_types := []table.Type{}
@@ -213,7 +222,6 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 				type_pos = p.prev_tok.position()
 				field_pos = field_start_pos.extend(type_pos)
 			}
-			// println(p.tok.position())
 			// Comments after type (same line)
 			comments << p.eat_comments()
 			if p.tok.kind == .lsbr {
@@ -226,8 +234,6 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 				if p.tok.kind == .assign {
 					// Default value
 					p.next()
-					// default_expr = p.tok.lit
-					// p.expr(0)
 					default_expr = p.expr(0)
 					match mut default_expr {
 						ast.EnumVal { default_expr.typ = typ }
@@ -275,13 +281,6 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 		last_line = p.tok.line_nr
 		p.check(.rcbr)
 	}
-	if language == .c {
-		name = 'C.$name'
-	} else if language == .js {
-		name = 'JS.$name'
-	} else {
-		name = p.prepend_mod(name)
-	}
 	t := table.TypeSymbol{
 		kind: .struct_
 		language: language
@@ -299,6 +298,10 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 		}
 		is_public: is_pub
 	}
+	if p.table.has_deep_child_no_ref(&t, name) {
+		p.error_with_pos('invalid recursive struct `$orig_name`', name_pos)
+		return ast.StructDecl{}
+	}
 	mut ret := 0
 	// println('reg type symbol $name mod=$p.mod')
 	ret = p.table.register_type_symbol(t)

vlib/v/parser/tests/invalid_recursive_struct1_err.out

@@ -0,0 +1,5 @@
+vlib/v/parser/tests/invalid_recursive_struct1_err.vv:1:8: error: invalid recursive struct `Human`
+    1 | struct Human {
+      |        ~~~~~
+    2 |     child Human
+    3 | }

vlib/v/parser/tests/invalid_recursive_struct1_err.vv

@@ -0,0 +1,3 @@
+struct Human {
+	child Human
+}

vlib/v/parser/tests/invalid_recursive_struct2_err.out

@@ -0,0 +1,7 @@
+vlib/v/parser/tests/invalid_recursive_struct2_err.vv:5:8: error: invalid recursive struct `Human`
+    3 | }
+    4 |
+    5 | struct Human {
+      |        ~~~~~
+    6 |     child Child
+    7 | }

vlib/v/parser/tests/invalid_recursive_struct2_err.vv

@@ -0,0 +1,7 @@
+struct Child {
+	be Human
+}
+
+struct Human {
+	child Child
+}

vlib/v/table/table.v

@@ -740,3 +740,18 @@ pub fn (table &Table) known_type_names() []string {
 	}
 	return res
 }
+
+// has_deep_child_no_ref returns true if type is struct and has any child or nested child with the type of the given name
+// the given name consists of module and name (`mod.Name`)
+// it doesn't care about childs that are references
+pub fn (table &Table) has_deep_child_no_ref(ts &TypeSymbol, name string) bool {
+	if ts.info is Struct {
+		for _, field in ts.info.fields {
+			sym := table.get_type_symbol(field.typ)
+			if !field.typ.is_ptr() && (sym.name == name || table.has_deep_child_no_ref(sym, name)) {
+				return true
+			}
+		}
+	}
+	return false
+}