checker: check goto label exists (#8523)

vlib/v/ast/ast.v

@@ -337,6 +337,7 @@ pub mut:
 	next_comments []Comment // coments that are one line after the decl; used for InterfaceDecl
 	source_file   &File = 0
 	scope         &Scope
+	label_names   []string
 }
 
 pub struct GenericParam {

vlib/v/checker/checker.v

@@ -3273,6 +3273,9 @@ fn (mut c Checker) stmt(node ast.Stmt) {
 		}
 		ast.GotoLabel {}
 		ast.GotoStmt {
+			if node.name !in c.cur_fn.label_names {
+				c.error('unknown label `$node.name`', node.pos)
+			}
 			// TODO: check label doesn't bypass variable declarations
 		}
 		ast.HashStmt {
@@ -5281,7 +5284,6 @@ pub fn (mut c Checker) offset_of(node ast.OffsetOf) table.Type {
 		c.error('first argument of __offsetof must be struct', node.pos)
 		return table.u32_type
 	}
-
 	if !c.table.struct_has_field(node.struct_type, node.field) {
 		c.error('struct `$sym.name` has no field called `$node.field`', node.pos)
 	}
@@ -5540,7 +5542,6 @@ fn (mut c Checker) fetch_and_verify_orm_fields(info table.Struct, pos token.Posi
 fn (mut c Checker) post_process_generic_fns() {
 	// Loop thru each generic function concrete type.
 	// Check each specific fn instantiation.
-
 	for i in 0 .. c.file.generic_fns.len {
 		if c.table.fn_gen_types.len == 0 {
 			// no concrete types, so just skip:
@@ -5689,7 +5690,6 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 	}
 	c.fn_scope = node.scope
 	c.stmts(node.stmts)
-
 	if c.fn_mut_arg_names.len > 0 {
 		c.fn_mut_arg_names.clear()
 	}

vlib/v/checker/tests/goto_label.out

@@ -0,0 +1,49 @@
+vlib/v/checker/tests/goto_label.vv:5:7: error: unknown label `a1`
+    3 |     goto f2
+    4 |     f1:
+    5 |     goto a1
+      |          ~~
+    6 |     _ = fn(){
+    7 |         goto f1
+vlib/v/checker/tests/goto_label.vv:7:8: error: unknown label `f1`
+    5 |     goto a1
+    6 |     _ = fn(){
+    7 |         goto f1
+      |              ~~
+    8 |         goto f2
+    9 |         goto a1
+vlib/v/checker/tests/goto_label.vv:8:8: error: unknown label `f2`
+    6 |     _ = fn(){
+    7 |         goto f1
+    8 |         goto f2
+      |              ~~
+    9 |         goto a1
+   10 |         a1:
+vlib/v/checker/tests/goto_label.vv:14:7: error: unknown label `a1`
+   12 |     }
+   13 |     f2:
+   14 |     goto a1
+      |          ~~
+   15 |     goto f1 // back
+   16 |     goto f2
+vlib/v/checker/tests/goto_label.vv:22:7: error: unknown label `f1`
+   20 |     goto g1 // forward
+   21 |     g1:
+   22 |     goto f1
+      |          ~~
+   23 |     goto a1
+   24 |     goto g1 // back
+vlib/v/checker/tests/goto_label.vv:23:7: error: unknown label `a1`
+   21 |     g1:
+   22 |     goto f1
+   23 |     goto a1
+      |          ~~
+   24 |     goto g1 // back
+   25 |     goto undefined
+vlib/v/checker/tests/goto_label.vv:25:7: error: unknown label `undefined`
+   23 |     goto a1
+   24 |     goto g1 // back
+   25 |     goto undefined
+      |          ~~~~~~~~~
+   26 | }
+   27 |

vlib/v/checker/tests/goto_label.vv

@@ -0,0 +1,32 @@
+fn f() {
+	goto f1 // forward
+	goto f2
+	f1:
+	goto a1
+	_ = fn(){
+		goto f1
+		goto f2
+		goto a1
+		a1:
+		goto a1
+	}
+	f2:
+	goto a1
+	goto f1 // back
+	goto f2
+}
+
+fn g() {
+	goto g1 // forward
+	g1:
+	goto f1
+	goto a1
+	goto g1 // back
+	goto undefined
+}
+
+// implicit main
+goto m1
+m1:
+goto m1
+

vlib/v/parser/fn.v

@@ -427,7 +427,9 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		is_builtin: p.builtin_mod || p.mod in util.builtin_module_parts
 		attrs: p.attrs
 		scope: p.scope
+		label_names: p.label_names
 	}
+	p.label_names = []
 	p.close_scope()
 	return fn_decl
 }
@@ -514,8 +516,13 @@ fn (mut p Parser) anon_fn() ast.AnonFn {
 		p.error_with_pos('unexpected `$p.tok.kind` after anonymous function signature, expecting `{`',
 			p.tok.position())
 	}
+	mut label_names := []string{}
 	if p.tok.kind == .lcbr {
+		tmp := p.label_names
+		p.label_names = []
 		stmts = p.parse_block_no_scope(false)
+		label_names = p.label_names
+		p.label_names = tmp
 	}
 	p.close_scope()
 	mut func := table.Fn{
@@ -542,6 +549,7 @@ fn (mut p Parser) anon_fn() ast.AnonFn {
 			pos: pos.extend(p.prev_tok.position())
 			file: p.file_name
 			scope: p.scope
+			label_names: label_names
 		}
 		typ: typ
 	}

vlib/v/parser/parser.v

@@ -69,6 +69,7 @@ mut:
 	warnings          []errors.Warning
 	vet_errors        []vet.Error
 	cur_fn_name       string
+	label_names       []string
 	in_generic_params bool // indicates if parsing between `<` and `>` of a method/function
 	name_error        bool // indicates if the token is not a name or the name is on another line
 }
@@ -552,6 +553,7 @@ pub fn (mut p Parser) top_stmt() ast.Stmt {
 						file: p.file_name
 						return_type: table.void_type
 						scope: p.scope
+						label_names: p.label_names
 					}
 				} else if p.pref.is_fmt {
 					return p.stmt(false)
@@ -656,6 +658,10 @@ pub fn (mut p Parser) stmt(is_top_level bool) ast.Stmt {
 				// `label:`
 				spos := p.tok.position()
 				name := p.check_name()
+				if name in p.label_names {
+					p.error_with_pos('duplicate label `$name`', spos)
+				}
+				p.label_names << name
 				p.next()
 				if p.tok.kind == .key_for {
 					mut stmt := p.stmt(is_top_level)