parser: implement infering generic type parameters from receiver types (fix #5862) (#9870)

vlib/v/ast/str.v

@@ -62,16 +62,28 @@ pub fn (node &FnDecl) stringify(t &Table, cur_mod string, m2a map[string]string)
 	if name in ['+', '-', '*', '/', '%', '<', '>', '==', '!=', '>=', '<='] {
 		f.write_string(' ')
 	}
+	mut add_para_types := true
 	if node.generic_names.len > 0 {
-		f.write_string('<')
-		for i, gname in node.generic_names {
-			is_last := i == node.generic_names.len - 1
-			f.write_string(gname)
-			if !is_last {
-				f.write_string(', ')
+		if node.is_method {
+			sym := t.get_type_symbol(node.params[0].typ)
+			if sym.info is Struct {
+				generic_names := sym.info.generic_types.map(t.get_type_symbol(it).name)
+				if generic_names == node.generic_names {
+					add_para_types = false
+				}
 			}
 		}
-		f.write_string('>')
+		if add_para_types {
+			f.write_string('<')
+			for i, gname in node.generic_names {
+				is_last := i == node.generic_names.len - 1
+				f.write_string(gname)
+				if !is_last {
+					f.write_string(', ')
+				}
+			}
+			f.write_string('>')
+		}
 	}
 	f.write_string('(')
 	for i, arg in node.params {

vlib/v/parser/fn.v

@@ -273,12 +273,13 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		}
 	}
 	// <T>
-	generic_names := p.parse_generic_names()
-	// check generic receiver method has no generic names
-	if is_method && rec.typ.has_flag(.generic) && generic_names.len == 0
-		&& p.table.get_type_symbol(rec.typ).kind != .any {
-		p.error_with_pos('generic receiver method `$name` should add generic names, e.g. $name<T>',
-			name_pos)
+	mut generic_names := p.parse_generic_names()
+	// generic names can be infer with receiver's generic names
+	if is_method && rec.typ.has_flag(.generic) && generic_names.len == 0 {
+		sym := p.table.get_type_symbol(rec.typ)
+		if sym.info is ast.Struct {
+			generic_names = sym.info.generic_types.map(p.table.get_type_symbol(it).name)
+		}
 	}
 	// Args
 	args2, are_args_type_only, is_variadic := p.fn_args()

vlib/v/parser/tests/generic_multiple_receiver_method_has_no_generic_names_err.out

@@ -1,7 +0,0 @@
-vlib/v/parser/tests/generic_multiple_receiver_method_has_no_generic_names_err.vv:6:20: error: generic receiver method `poll` should add generic names, e.g. poll<T>
-    4 | }
-    5 |
-    6 | fn (q Queue<A, B>) poll() A {
-      |                    ~~~~
-    7 |     return q.buffer[0]
-    8 | }

vlib/v/parser/tests/generic_multiple_receiver_method_has_no_generic_names_err.vv

@@ -1,13 +0,0 @@
-struct Queue<A, B>{
-	buffer []A
-	size   B
-}
-
-fn (q Queue<A, B>) poll() A {
-	return q.buffer[0]
-}
-
-fn main() {
-	q := Queue<string, int>{}
-	println(q)
-}

vlib/v/parser/tests/generic_receiver_method_has_no_generic_names_err.out

@@ -1,7 +0,0 @@
-vlib/v/parser/tests/generic_receiver_method_has_no_generic_names_err.vv:5:17: error: generic receiver method `poll` should add generic names, e.g. poll<T>
-    3 | }
-    4 |
-    5 | fn (q Queue<T>) poll() T {
-      |                 ~~~~
-    6 |     return q.buffer[0]
-    7 | }

vlib/v/parser/tests/generic_receiver_method_has_no_generic_names_err.vv

@@ -1,12 +0,0 @@
-struct Queue<T>{
-	buffer []T
-}
-
-fn (q Queue<T>) poll() T {
-	return q.buffer[0]
-}
-
-fn main() {
-	q := Queue<int>{}
-	println(q)
-}

vlib/v/tests/generics_call_with_reference_arg_test.v

@@ -4,7 +4,7 @@ mut:
 	buffer []&T
 }
 
-fn (mut s MyStruct<T>) add<T>(e &T) bool {
+fn (mut s MyStruct<T>) add(e &T) bool {
 	s.buffer[0] = e
 	return true
 }

vlib/v/tests/generics_method_on_receiver_types_test.v

@@ -0,0 +1,13 @@
+struct Abc<T> {
+	value T
+}
+
+fn (s Abc<T>) get_value() T {
+	return s.value
+}
+
+fn test_generics_method_on_receiver_types() {
+	s := Abc<string>{'hello'}
+	println(s.get_value())
+	assert s.get_value() == 'hello'
+}

vlib/v/tests/generics_with_embed_generics_test.v

@@ -18,7 +18,7 @@ fn group_new<T>(val ...T) Group<T> {
 	return g
 }
 
-fn (mut it Group<T>) next<T>() ?T {
+fn (mut it Group<T>) next() ?T {
 	if it.index >= it.len {
 		return none
 	}

vlib/v/tests/generics_with_generics_struct_receiver_test.v

@@ -2,7 +2,7 @@ struct Num<T> {
 	num T
 }
 
-fn (num Num<T>) is_autom<T>() bool {
+fn (num Num<T>) is_autom() bool {
 	return true
 }
 

vlib/v/tests/generics_with_multiple_generics_struct_receiver_test.v

@@ -3,7 +3,7 @@ struct Foo<A, B> {
 	b B
 }
 
-fn (num Foo<A, B>) get_foo1<A, B>() (A, B) {
+fn (num Foo<A, B>) get_foo1() (A, B) {
 	return num.a, num.b
 }