parser, checker, cgen: implement generics anon fn (#15529)

vlib/v/checker/return.v

@@ -122,6 +122,11 @@ pub fn (mut c Checker) return_stmt(mut node ast.Return) {
 				}
 				continue
 			}
+			if got_typ_sym.kind == .function && exp_typ_sym.kind == .function {
+				if (got_typ_sym.info as ast.FnType).is_anon {
+					continue
+				}
+			}
 			pos := node.exprs[expr_idxs[i]].pos()
 			c.error('cannot use `$got_typ_sym.name` as type `${c.table.type_to_str(exp_type)}` in return argument',
 				pos)

vlib/v/gen/c/fn.v

@@ -445,14 +445,19 @@ fn closure_ctx(node ast.FnDecl) string {
 
 fn (mut g Gen) gen_anon_fn(mut node ast.AnonFn) {
 	g.gen_anon_fn_decl(mut node)
+	mut fn_name := node.decl.name
+	if node.decl.generic_names.len > 0 {
+		fn_name = g.generic_fn_name(g.cur_concrete_types, fn_name, true)
+	}
+
 	if !node.decl.scope.has_inherited_vars() {
-		g.write(node.decl.name)
+		g.write(fn_name)
 		return
 	}
 	ctx_struct := closure_ctx(node.decl)
 	// it may be possible to optimize `memdup` out if the closure never leaves current scope
 	// TODO in case of an assignment, this should only call "__closure_set_data" and "__closure_set_function" (and free the former data)
-	g.write('__closure_create($node.decl.name, ($ctx_struct*) memdup_uncollectable(&($ctx_struct){')
+	g.write('__closure_create($fn_name, ($ctx_struct*) memdup_uncollectable(&($ctx_struct){')
 	g.indent++
 	for var in node.inherited_vars {
 		g.writeln('.$var.name = $var.name,')

vlib/v/parser/fn.v

@@ -677,7 +677,7 @@ fn (mut p Parser) anon_fn() ast.AnonFn {
 	}
 	p.scope.detached_from_parent = true
 	inherited_vars := if p.tok.kind == .lsbr { p.closure_vars() } else { []ast.Param{} }
-	// TODO generics
+	_, generic_names := p.parse_generic_types()
 	args, _, is_variadic := p.fn_args()
 	for arg in args {
 		if arg.name.len == 0 && p.table.sym(arg.typ).kind != .placeholder {
@@ -759,6 +759,7 @@ fn (mut p Parser) anon_fn() ast.AnonFn {
 			params: args
 			is_variadic: is_variadic
 			is_method: false
+			generic_names: generic_names
 			is_anon: true
 			no_body: no_body
 			pos: pos.extend(p.prev_tok.pos())

vlib/v/tests/generics_closure_fn_test.v

@@ -0,0 +1,20 @@
+fn setter<T>(mut m map[T]int) fn (T, int) {
+	return fn [mut m] <T>(x T, k int) {
+		m[x] = k
+	}
+}
+
+fn test_generics_closure_fn() {
+	mut m := {
+		f32(0.1): 1
+	}
+
+	f := setter(mut m)
+	f(0.2, 2)
+
+	println(m)
+	assert m == {
+		f32(0.1): 1
+		0.2:      2
+	}
+}