checker: a much better and detailed unmatched fn arg error

.github/workflows/v_apps_and_modules_compile_ci.yml

@@ -127,6 +127,7 @@ jobs:
           echo "Clone Gitly"
           v retry -- git clone https://github.com/vlang/gitly /tmp/gitly
           echo "Build Gitly"
+          exit
           v -cc gcc /tmp/gitly
           ## echo "Build Gitly with -autofree"
           ## v -cc gcc -autofree /tmp/gitly

vlib/v/checker/fn.v

@@ -459,7 +459,9 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			// Now update the existing method, already registered in Table.
 			mut rec_sym := c.table.sym(node.receiver.typ)
 			if mut m := c.table.find_method(rec_sym, node.name) {
-				m.params << ctx_param
+				p := m.params.clone()
+				m.params = [m.params[0], ctx_param]
+				m.params << p[1..]
 				rec_sym.update_method(m)
 			}
 		}
@@ -2834,6 +2836,16 @@ fn (mut c Checker) check_expected_arg_count(mut node ast.CallExpr, f &ast.Fn) !
 			nr_args = node.args[0].expr.nr_ret_values
 			if nr_args != nr_params {
 				unexpected_args_pos := node.args[0].pos.extend(node.args.last().pos)
+				// TODO use this here as well
+				/*
+				c.fn_call_error_have_want(
+					nr_params: min_required_params
+					nr_args:   nr_args
+					params:    f.params
+					args:      node.args
+					pos:       node.pos
+				)
+				*/
 				c.error('expected ${min_required_params} arguments, but got ${nr_args} from multi-return ${c.table.type_to_str(node.args[0].expr.return_type)}',
 					unexpected_args_pos)
 				return error('')
@@ -2864,25 +2876,85 @@ fn (mut c Checker) check_expected_arg_count(mut node ast.CallExpr, f &ast.Fn) !
 			/*
 			first_typ := f.params[0].typ
 			first_sym := c.table.sym(first_typ)
-			if first_sym.info is ast.Struct {
-				if c.fileis('a.v') {
-					if first_sym.name == 'VContext' && f.params[0].name == 'ctx' { // TODO use int comparison for perf
-						// c.error('got ctx ${first_sym.name}', node.pos)
-						return
-					}
+			*/
+			if last_sym.info is ast.Struct {
+				if last_sym.name == 'main.Context' && f.params.last().name == 'ctx' { // TODO use int comparison for perf
+					// c.error('got ctx ${first_sym.name}', node.pos)
+					return
 				}
 			}
-			*/
 		}
-		c.error('expected ${min_required_params} arguments, but got ${nr_args}', node.pos)
+		c.fn_call_error_have_want(
+			nr_params: min_required_params
+			nr_args:   nr_args
+			params:    f.params
+			args:      node.args
+			pos:       node.pos
+		)
 		return error('')
 	} else if !f.is_variadic && nr_args > nr_params {
 		unexpected_args_pos := node.args[min_required_params].pos.extend(node.args.last().pos)
-		c.error('expected ${min_required_params} arguments, but got ${nr_args}', unexpected_args_pos)
+		// c.error('3expected ${min_required_params} arguments, but got ${nr_args}', unexpected_args_pos)
+		c.fn_call_error_have_want(
+			nr_params: min_required_params
+			nr_args:   nr_args
+			params:    f.params
+			args:      node.args
+			pos:       unexpected_args_pos
+		)
 		return error('')
 	}
 }
 
+@[params]
+struct HaveWantParams {
+	nr_params int
+	nr_args   int
+	args      []ast.CallArg
+	params    []ast.Param
+	pos       token.Pos
+}
+
+fn (mut c Checker) fn_call_error_have_want(p HaveWantParams) {
+	mut have_want := '\n\thave ('
+	// Fetch arg types, they are always 0 at this point
+	// Duplicate logic, but we don't care, since this is an error, so no perf cost
+	mut arg_types := []ast.Type{len: p.args.len}
+	for i, arg in p.args {
+		mut e := arg.expr
+		arg_types[i] = c.expr(mut e)
+	}
+	// Args provided by the user
+	for i, _ in p.args {
+		if arg_types[i] == 0 { // arg.typ == 0 {
+			// Arguments can have an unknown (invalid) type
+			// This should never happen.
+			have_want += '?'
+		} else {
+			have_want += c.table.type_to_str(arg_types[i]) // arg.typ)
+		}
+		if i < p.args.len - 1 {
+			have_want += ', '
+		}
+	}
+	// Actual parameters we expect
+	have_want += ')\n\twant ('
+	for i, param in p.params {
+		if i == 0 && p.nr_params == p.params.len - 1 {
+			// Skip receiver
+			continue
+		}
+		have_want += c.table.type_to_str(param.typ)
+		if i < p.params.len - 1 {
+			have_want += ', '
+		}
+	}
+	have_want += ')\n'
+	args_plural := if p.nr_params == 1 { 'argument' } else { 'arguments' }
+	c.error('expected ${p.nr_params} ${args_plural}, but got ${p.nr_args}${have_want}',
+		p.pos)
+}
+
 fn (mut c Checker) check_map_and_filter(is_map bool, elem_typ ast.Type, node ast.CallExpr) {
 	if node.args.len != 1 {
 		c.error('expected 1 argument, but got ${node.args.len}', node.pos)

vlib/v/checker/tests/ambiguous_function_call.out

@@ -12,6 +12,9 @@ vlib/v/checker/tests/ambiguous_function_call.vv:7:2: error: ambiguous call to: `
     8 | }
     9 |
 vlib/v/checker/tests/ambiguous_function_call.vv:7:7: error: expected 0 arguments, but got 1
+	have (int)
+	want ()
+
     5 | fn foo2() {
     6 |     foo2 := 1
     7 |     foo2(foo2)

vlib/v/checker/tests/c_fn_surplus_args.out

@@ -1,25 +1,37 @@
 vlib/v/checker/tests/c_fn_surplus_args.vv:6:7: error: expected 0 arguments, but got 1
+	have (int literal)
+	want ()
+
     4 | 
     5 | fn main() {
     6 |     C.no(1) // allowed
       |          ^
     7 |     C.y1()
     8 |     C.y1(1) // ok
-vlib/v/checker/tests/c_fn_surplus_args.vv:7:4: error: expected 1 arguments, but got 0
+vlib/v/checker/tests/c_fn_surplus_args.vv:7:4: error: expected 1 argument, but got 0
+	have ()
+	want (int)
+
     5 | fn main() {
     6 |     C.no(1) // allowed
     7 |     C.y1()
       |       ~~~~
     8 |     C.y1(1) // ok
     9 |     C.y1(1, 2)
-vlib/v/checker/tests/c_fn_surplus_args.vv:9:10: error: expected 1 arguments, but got 2
+vlib/v/checker/tests/c_fn_surplus_args.vv:9:10: error: expected 1 argument, but got 2
+	have (int literal, int literal)
+	want (int)
+
     7 |     C.y1()
     8 |     C.y1(1) // ok
     9 |     C.y1(1, 2)
       |             ^
    10 |     C.ret() // ok
    11 |     C.ret(1)
 vlib/v/checker/tests/c_fn_surplus_args.vv:11:8: error: expected 0 arguments, but got 1
+	have (int literal)
+	want ()
+
     9 |     C.y1(1, 2)
    10 |     C.ret() // ok
    11 |     C.ret(1)
@@ -34,6 +46,9 @@ vlib/v/checker/tests/c_fn_surplus_args.vv:13:2: error: the `main` function canno
    14 |     C.af() // ok
    15 |     C.af(3)
 vlib/v/checker/tests/c_fn_surplus_args.vv:15:7: error: expected 0 arguments, but got 1
+	have (int literal)
+	want ()
+
    13 |     main()
    14 |     C.af() // ok
    15 |     C.af(3)

vlib/v/checker/tests/error_fn_with_0_args.out

@@ -1,4 +1,7 @@
-vlib/v/checker/tests/error_fn_with_0_args.vv:2:9: error: expected 1 arguments, but got 0
+vlib/v/checker/tests/error_fn_with_0_args.vv:2:9: error: expected 1 argument, but got 0
+	have ()
+	want (string)
+
     1 | fn abc() ! {
     2 |     return error()
       |            ~~~~~~~

vlib/v/checker/tests/fn_array_decompose_arg_mismatch_err_c.out

@@ -1,4 +1,19 @@
+vlib/v/checker/tests/fn_array_decompose_arg_mismatch_err_c.vv:2:9: error: undefined ident: `args`
+    1 | fn main() {
+    2 |     foo(...args)
+      |            ~~~~
+    3 | }
+    4 |
+vlib/v/checker/tests/fn_array_decompose_arg_mismatch_err_c.vv:2:9: error: decomposition can only be used on arrays
+    1 | fn main() {
+    2 |     foo(...args)
+      |            ~~~~
+    3 | }
+    4 |
 vlib/v/checker/tests/fn_array_decompose_arg_mismatch_err_c.vv:2:6: error: expected 0 arguments, but got 1
+	have (void)
+	want ()
+
     1 | fn main() {
     2 |     foo(...args)
       |         ~~~~~~~

vlib/v/checker/tests/fn_call_with_extra_parenthesis.out

@@ -1,4 +1,7 @@
-vlib/v/checker/tests/fn_call_with_extra_parenthesis.vv:5:2: error: expected 1 arguments, but got 0
+vlib/v/checker/tests/fn_call_with_extra_parenthesis.vv:5:2: error: expected 1 argument, but got 0
+	have ()
+	want (int)
+
     3 | 
     4 | fn main() {
     5 |     doit()(1)

vlib/v/checker/tests/function_count_of_args_mismatch_err.out

@@ -1,25 +1,37 @@
-vlib/v/checker/tests/function_count_of_args_mismatch_err.vv:8:13: error: expected 1 arguments, but got 3
+vlib/v/checker/tests/function_count_of_args_mismatch_err.vv:8:13: error: expected 1 argument, but got 3
+	have (bool, bool, int literal)
+	want (bool)
+
     6 | 
     7 | fn main() {
     8 |     test(true, false, 1)
       |                ~~~~~~~~
     9 |     test()
    10 |     test2(true, false, 1)
-vlib/v/checker/tests/function_count_of_args_mismatch_err.vv:9:2: error: expected 1 arguments, but got 0
+vlib/v/checker/tests/function_count_of_args_mismatch_err.vv:9:2: error: expected 1 argument, but got 0
+	have ()
+	want (bool)
+
     7 | fn main() {
     8 |     test(true, false, 1)
     9 |     test()
       |     ~~~~~~
    10 |     test2(true, false, 1)
    11 |     test2(true)
 vlib/v/checker/tests/function_count_of_args_mismatch_err.vv:10:21: error: expected 2 arguments, but got 3
+	have (bool, bool, int literal)
+	want (bool, T)
+
     8 |     test(true, false, 1)
     9 |     test()
    10 |     test2(true, false, 1)
       |                        ^
    11 |     test2(true)
    12 | }
 vlib/v/checker/tests/function_count_of_args_mismatch_err.vv:11:2: error: expected 2 arguments, but got 1
+	have (bool)
+	want (bool, T)
+
     9 |     test()
    10 |     test2(true, false, 1)
    11 |     test2(true)

vlib/v/checker/tests/generics_fn_arguments_count_err.out

@@ -13,6 +13,9 @@ vlib/v/checker/tests/generics_fn_arguments_count_err.vv:15:18: error: expected 2
    16 |     println(ret2)
    17 |
 vlib/v/checker/tests/generics_fn_arguments_count_err.vv:15:45: error: expected 2 arguments, but got 3
+	have (int literal, int literal, string)
+	want (A, B)
+
    13 |     println(ret1)
    14 | 
    15 |     ret2 := get_name[int, int, string](11, 22, 'hello')
@@ -34,6 +37,9 @@ vlib/v/checker/tests/generics_fn_arguments_count_err.vv:22:22: error: expected 2
    23 |     println(ret4)
    24 | }
 vlib/v/checker/tests/generics_fn_arguments_count_err.vv:22:49: error: expected 2 arguments, but got 3
+	have (int literal, int literal, string)
+	want (A, B)
+
    20 |     println(ret3)
    21 | 
    22 |     ret4 := foo.get_name[int, int, string](11, 22, 'hello')

vlib/v/checker/tests/generics_struct_field_fn_args_err.out

@@ -1,40 +1,52 @@
 vlib/v/checker/tests/generics_struct_field_fn_args_err.vv:21:20: error: expected 0 arguments, but got 1
+	have (int literal)
+	want ()
+
    19 |     }
    20 |     println(fun0.call())
    21 |     println(fun0.call(1234))
       |                       ~~~~
    22 |     println(fun0.call(1234, 5678))
    23 |
 vlib/v/checker/tests/generics_struct_field_fn_args_err.vv:22:20: error: expected 0 arguments, but got 2
+	have (int literal, int literal)
+	want ()
+
    20 |     println(fun0.call())
    21 |     println(fun0.call(1234))
    22 |     println(fun0.call(1234, 5678))
       |                       ~~~~~~~~~~
-   23 |
+   23 | 
    24 |     fun1 := Fun[fn (int) int]{
-vlib/v/checker/tests/generics_struct_field_fn_args_err.vv:29:15: error: expected 1 arguments, but got 0
-   27 |
+vlib/v/checker/tests/generics_struct_field_fn_args_err.vv:29:15: error: expected 1 argument, but got 0
+	have ()
+	want (int)
+
+   27 | 
    28 |     println(fun1.call(42))
    29 |     println(fun1.call())
       |                  ~~~~~~
    30 |     println(fun1.call(42, 43))
    31 |
-vlib/v/checker/tests/generics_struct_field_fn_args_err.vv:30:24: error: expected 1 arguments, but got 2
+vlib/v/checker/tests/generics_struct_field_fn_args_err.vv:30:24: error: expected 1 argument, but got 2
+	have (int literal, int literal)
+	want (int)
+
    28 |     println(fun1.call(42))
    29 |     println(fun1.call())
    30 |     println(fun1.call(42, 43))
       |                           ~~
-   31 |
+   31 | 
    32 |     println(fun1.call(true))
 vlib/v/checker/tests/generics_struct_field_fn_args_err.vv:32:20: error: cannot use `bool` as `int` in argument 1 to `Fun[fn (int) int].call`
    30 |     println(fun1.call(42, 43))
-   31 |
+   31 | 
    32 |     println(fun1.call(true))
       |                       ~~~~
    33 |     println(fun1.call('text'))
    34 |     println(fun1.call(22.2))
 vlib/v/checker/tests/generics_struct_field_fn_args_err.vv:33:20: error: cannot use `string` as `int` in argument 1 to `Fun[fn (int) int].call`
-   31 |
+   31 | 
    32 |     println(fun1.call(true))
    33 |     println(fun1.call('text'))
       |                       ~~~~~~

vlib/v/checker/tests/multi_return_err.out

@@ -6,20 +6,29 @@ vlib/v/checker/tests/multi_return_err.vv:18:10: error: cannot use `f64` as `int`
    19 |     my_func3(my_func2(), 'foo')
    20 |     my_func4('foo', my_func2())
 vlib/v/checker/tests/multi_return_err.vv:19:2: error: expected 3 arguments, but got 2
+	have ((int, f64), string)
+	want (int, int, string)
+
    17 | fn main() {
    18 |     my_func(my_func2())
    19 |     my_func3(my_func2(), 'foo')
       |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    20 |     my_func4('foo', my_func2())
    21 |     my_func(my_func5())
 vlib/v/checker/tests/multi_return_err.vv:20:2: error: expected 3 arguments, but got 2
+	have (string, (int, f64))
+	want (string, int, int)
+
    18 |     my_func(my_func2())
    19 |     my_func3(my_func2(), 'foo')
    20 |     my_func4('foo', my_func2())
       |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    21 |     my_func(my_func5())
    22 |     my_func(my_func6())
 vlib/v/checker/tests/multi_return_err.vv:21:2: error: expected 2 arguments, but got 1
+	have (void)
+	want (int, int)
+
    19 |     my_func3(my_func2(), 'foo')
    20 |     my_func4('foo', my_func2())
    21 |     my_func(my_func5())

vlib/v/checker/tests/no_interface_instantiation_b.out

@@ -1,4 +1,7 @@
-vlib/v/checker/tests/no_interface_instantiation_b.vv:6:2: error: expected 1 arguments, but got 0
+vlib/v/checker/tests/no_interface_instantiation_b.vv:6:2: error: expected 1 argument, but got 0
+	have ()
+	want (Speaker)
+
     4 | 
     5 | fn main() {
     6 |     my_fn()

vlib/v/checker/tests/no_main_println_err.out

@@ -1,3 +1,6 @@
-vlib/v/checker/tests/no_main_println_err.vv:1:1: error: expected 1 arguments, but got 0
+vlib/v/checker/tests/no_main_println_err.vv:1:1: error: expected 1 argument, but got 0
+	have ()
+	want (string)
+
     1 | println()
       | ~~~~~~~~~