checker: detect unknown type to iterate with $for (#8971)

vlib/v/ast/ast.v

@@ -723,6 +723,7 @@ pub:
 	stmts   []Stmt
 	kind    CompForKind
 	pos     token.Position
+	typ_pos token.Position
 pub mut:
 	// expr    Expr
 	typ table.Type

vlib/v/checker/checker.v

@@ -3109,7 +3109,12 @@ fn (mut c Checker) stmt(node ast.Stmt) {
 			c.branch_stmt(node)
 		}
 		ast.CompFor {
-			// node.typ = c.expr(node.expr)
+			if node.typ > table.void_type {
+				sym := c.table.get_type_symbol(node.typ)
+				if sym.kind == .placeholder {
+					c.error('unknown type `$sym.name`', node.typ_pos)
+				}
+			}
 			c.stmts(node.stmts)
 		}
 		ast.ConstDecl {

vlib/v/checker/tests/comptime_for.out

@@ -0,0 +1,12 @@
+vlib/v/checker/tests/comptime_for.vv:2:12: error: unknown type `Huh`
+    1 | fn unknown() {
+    2 |     $for m in Huh.methods {}
+      |               ~~~
+    3 |     $for f in Huh.fields {}
+    4 | }
+vlib/v/checker/tests/comptime_for.vv:3:12: error: unknown type `Huh`
+    1 | fn unknown() {
+    2 |     $for m in Huh.methods {}
+    3 |     $for f in Huh.fields {}
+      |               ~~~
+    4 | }

vlib/v/checker/tests/comptime_for.vv

@@ -0,0 +1,4 @@
+fn unknown() {
+	$for m in Huh.methods {}
+	$for f in Huh.fields {}
+}

vlib/v/parser/comptime.v

@@ -217,10 +217,13 @@ fn (mut p Parser) comp_for() ast.CompFor {
 	// $for field in App(fields) {
 	p.next()
 	p.check(.key_for)
+	var_pos := p.tok.position()
 	val_var := p.check_name()
 	p.check(.key_in)
+	mut typ_pos := p.tok.position()
 	lang := p.parse_language()
 	typ := p.parse_any_type(lang, false, false)
+	typ_pos = typ_pos.extend(p.prev_tok.position())
 	p.check(.dot)
 	for_val := p.check_name()
 	mut kind := ast.CompForKind.methods
@@ -228,15 +231,18 @@ fn (mut p Parser) comp_for() ast.CompFor {
 		p.scope.register(ast.Var{
 			name: val_var
 			typ: p.table.find_type_idx('FunctionData')
+			pos: var_pos
 		})
 	} else if for_val == 'fields' {
 		p.scope.register(ast.Var{
 			name: val_var
 			typ: p.table.find_type_idx('FieldData')
+			pos: var_pos
 		})
 		kind = .fields
 	} else {
-		p.error('unknown kind `$for_val`, available are: `methods` or `fields`')
+		p.error_with_pos('unknown kind `$for_val`, available are: `methods` or `fields`',
+			p.prev_tok.position())
 		return ast.CompFor{}
 	}
 	spos := p.tok.position()
@@ -246,6 +252,7 @@ fn (mut p Parser) comp_for() ast.CompFor {
 		stmts: stmts
 		kind: kind
 		typ: typ
+		typ_pos: typ_pos
 		pos: spos.extend(p.tok.position())
 	}
 }