checker: fix generic lambda type binding resolution (fix #22109) (#22115)

vlib/v/checker/check_types.v

@@ -1069,6 +1069,15 @@ fn (mut c Checker) infer_fn_generic_types(func ast.Fn, mut node ast.CallExpr) {
 							if param_sym.info.func.return_type.nr_muls() > 0 && typ.nr_muls() > 0 {
 								typ = typ.set_nr_muls(0)
 							}
+							// resolve lambda with generic return type
+							if arg.expr is ast.LambdaExpr && typ.has_flag(.generic) {
+								typ = c.comptime.resolve_generic_expr(arg.expr.expr, typ)
+								if typ.has_flag(.generic) {
+									lambda_ret_gt_name := c.table.type_to_str(typ)
+									idx := func.generic_names.index(lambda_ret_gt_name)
+									typ = node.concrete_types[idx]
+								}
+							}
 						}
 					}
 				} else if arg_sym.kind in [.struct_, .interface_, .sum_type] {

vlib/v/checker/fn.v

@@ -447,7 +447,7 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			}
 			node.params = [node.params[0], ctx_param]
 			node.params << params[1..]
-			println('new params ${node.name}')
+			// println('new params ${node.name}')
 			// println(node.params)
 		}
 		// sym := c.table.sym(typ_veb_context)

vlib/v/checker/return.v

@@ -261,6 +261,11 @@ fn (mut c Checker) return_stmt(mut node ast.Return) {
 				} else {
 					got_type_sym.name
 				}
+				// ignore generic casting expr on lambda in this phase
+				if c.inside_lambda && exp_type.has_flag(.generic)
+					&& node.exprs[expr_idxs[i]] is ast.CastExpr {
+					continue
+				}
 				c.error('cannot use `${got_type_name}` as ${c.error_type_name(exp_type)} in return argument',
 					pos)
 			}

vlib/v/comptime/comptimeinfo.v

@@ -279,6 +279,36 @@ fn (mut ct ComptimeInfo) comptime_get_kind_var(var ast.Ident) ?ast.ComptimeForKi
 	}
 }
 
+pub fn (mut ct ComptimeInfo) resolve_generic_expr(expr ast.Expr, default_typ ast.Type) ast.Type {
+	match expr {
+		ast.ParExpr {
+			return ct.resolve_generic_expr(expr.expr, default_typ)
+		}
+		ast.CastExpr {
+			return expr.typ
+		}
+		ast.InfixExpr {
+			if ct.is_comptime_var(expr.left) {
+				return ct.resolver.unwrap_generic(ct.get_comptime_var_type(expr.left))
+			}
+			if ct.is_comptime_var(expr.right) {
+				return ct.resolver.unwrap_generic(ct.get_comptime_var_type(expr.right))
+			}
+			return default_typ
+		}
+		ast.Ident {
+			return if ct.is_comptime_var(expr) {
+				ct.resolver.unwrap_generic(ct.get_comptime_var_type(expr))
+			} else {
+				default_typ
+			}
+		}
+		else {
+			return default_typ
+		}
+	}
+}
+
 pub struct DummyResolver {
 mut:
 	file &ast.File = unsafe { nil }

vlib/v/gen/c/fn.v

@@ -1469,39 +1469,12 @@ fn (mut g Gen) resolve_receiver_name(node ast.CallExpr, unwrapped_rec_type ast.T
 	return receiver_type_name
 }
 
-fn (mut g Gen) resolve_generic_expr(expr ast.Expr, default_typ ast.Type) ast.Type {
-	match expr {
-		ast.ParExpr {
-			return g.resolve_generic_expr(expr.expr, default_typ)
-		}
-		ast.InfixExpr {
-			if g.comptime.is_comptime_var(expr.left) {
-				return g.unwrap_generic(g.comptime.get_comptime_var_type(expr.left))
-			}
-			if g.comptime.is_comptime_var(expr.right) {
-				return g.unwrap_generic(g.comptime.get_comptime_var_type(expr.right))
-			}
-			return default_typ
-		}
-		ast.Ident {
-			return if g.comptime.is_comptime_var(expr) {
-				g.unwrap_generic(g.comptime.get_comptime_var_type(expr))
-			} else {
-				default_typ
-			}
-		}
-		else {
-			return default_typ
-		}
-	}
-}
-
 fn (mut g Gen) resolve_receiver_type(node ast.CallExpr) (ast.Type, &ast.TypeSymbol) {
 	left_type := g.unwrap_generic(node.left_type)
 	mut unwrapped_rec_type := node.receiver_type
 	if g.cur_fn != unsafe { nil } && g.cur_fn.generic_names.len > 0 { // in generic fn
 		unwrapped_rec_type = g.unwrap_generic(node.receiver_type)
-		unwrapped_rec_type = g.resolve_generic_expr(node.left, unwrapped_rec_type)
+		unwrapped_rec_type = g.comptime.resolve_generic_expr(node.left, unwrapped_rec_type)
 	} else { // in non-generic fn
 		sym := g.table.sym(node.receiver_type)
 		match sym.info {

vlib/v/tests/generic_lambda_expr_test.v

@@ -0,0 +1,15 @@
+pub fn mymap[T, R](input []T, f fn (T) R) []R {
+	mut results := []R{cap: input.len}
+	for x in input {
+		results << f(x)
+	}
+	return results
+}
+
+fn test_main() {
+	assert dump(mymap([1, 2, 3, 4, 5], fn (i int) int {
+		return i * i
+	})) == [1, 4, 9, 16, 25]
+	assert dump(mymap([1, 2, 3, 4, 5], |x| x * x)) == [1, 4, 9, 16, 25]
+	assert dump(mymap([1, 2, 3, 4, 5], |x| u16(x * x))) == [u16(1), 4, 9, 16, 25]
+}