checker: make a calling no-body function a checker error (#8265)

vlib/v/checker/checker.v

@@ -1432,6 +1432,10 @@ pub fn (mut c Checker) call_method(mut call_expr ast.CallExpr) table.Type {
 			c.fail_if_immutable(call_expr.left)
 			// call_expr.is_mut = true
 		}
+		if (!left_type_sym.is_builtin() && method.mod != 'builtin') && method.language == .v
+			&& method.no_body {
+			c.error('cannot call a method that does not have a body', call_expr.pos)
+		}
 		if method.return_type == table.void_type && method.ctdefine.len > 0
 			&& method.ctdefine !in c.pref.compile_defines {
 			call_expr.should_be_skipped = true
@@ -1726,6 +1730,9 @@ pub fn (mut c Checker) call_fn(mut call_expr ast.CallExpr) table.Type {
 		// builtin C.m*, C.s* only - temp
 		c.warn('function `$f.name` must be called from an `unsafe` block', call_expr.pos)
 	}
+	if f.mod != 'builtin' && f.language == .v && f.no_body {
+		c.error('cannot call a function that does not have a body', call_expr.pos)
+	}
 	for generic_type in call_expr.generic_types {
 		sym := c.table.get_type_symbol(generic_type)
 		if sym.kind == .placeholder {

vlib/v/checker/tests/fn_call_no_body.out

@@ -0,0 +1,13 @@
+vlib/v/checker/tests/fn_call_no_body.vv:7:9: error: cannot call a method that does not have a body
+    5 |
+    6 | fn main() {
+    7 |     Foo(0).f()
+      |            ~~~
+    8 |     f()
+    9 | }
+vlib/v/checker/tests/fn_call_no_body.vv:8:2: error: cannot call a function that does not have a body
+    6 | fn main() {
+    7 |     Foo(0).f()
+    8 |     f()
+      |     ~~~
+    9 | }

vlib/v/checker/tests/fn_call_no_body.vv

@@ -0,0 +1,9 @@
+type Foo = int
+fn (_ Foo) f()
+
+fn f()
+
+fn main() {
+	Foo(0).f()
+	f()
+}

vlib/v/parser/fn.v

@@ -315,6 +315,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		return_type = p.parse_type()
 	}
 	mut type_sym_method_idx := 0
+	no_body := p.tok.kind != .lcbr
 	// Register
 	if is_method {
 		mut type_sym := p.table.get_type_symbol(rec_type)
@@ -345,6 +346,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 			is_pub: is_pub
 			is_deprecated: is_deprecated
 			is_unsafe: is_unsafe
+			no_body: no_body
 			mod: p.mod
 			attrs: p.attrs
 		})
@@ -369,6 +371,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 			is_pub: is_pub
 			is_deprecated: is_deprecated
 			is_unsafe: is_unsafe
+			no_body: no_body
 			mod: p.mod
 			attrs: p.attrs
 			language: language
@@ -378,7 +381,6 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 	// Body
 	p.cur_fn_name = name
 	mut stmts := []ast.Stmt{}
-	no_body := p.tok.kind != .lcbr
 	body_start_pos := p.peek_tok.position()
 	if p.tok.kind == .lcbr {
 		p.inside_fn = true

vlib/v/table/table.v

@@ -32,6 +32,7 @@ pub:
 	is_deprecated  bool
 	is_unsafe      bool
 	is_placeholder bool
+	no_body        bool
 	mod            string
 	ctdefine       string // compile time define. myflag, when [if myflag] tag
 	attrs          []Attr

vlib/v/table/types.v

@@ -573,6 +573,11 @@ pub fn (t &TypeSymbol) is_primitive() bool {
 	return t.is_number() || t.is_pointer() || t.is_string()
 }
 
+[inline]
+pub fn (t &TypeSymbol) is_builtin() bool {
+	return t.mod == 'builtin'
+}
+
 // for debugging/errors only, perf is not an issue
 pub fn (k Kind) str() string {
 	k_str := match k {