ast, parser, checker: fix generic fn in builtin module (#12769)

vlib/v/ast/table.v

@@ -1153,8 +1153,12 @@ pub fn (t &Table) mktyp(typ Type) Type {
 	}
 }
 
+pub fn (mut t Table) register_fn_generic_types(fn_name string) {
+	t.fn_generic_types[fn_name] = [][]Type{}
+}
+
 pub fn (mut t Table) register_fn_concrete_types(fn_name string, types []Type) bool {
-	mut a := t.fn_generic_types[fn_name]
+	mut a := t.fn_generic_types[fn_name] or { return false }
 	if types in a {
 		return false
 	}

vlib/v/checker/checker.v

@@ -1986,17 +1986,15 @@ pub fn (mut c Checker) method_call(mut node ast.CallExpr) ast.Type {
 		// c.error('`void` type has no methods', node.left.position())
 		return ast.void_type
 	}
-	mut has_generic := false // x.foo<T>() instead of x.foo<int>()
 	mut concrete_types := []ast.Type{}
 	for concrete_type in node.concrete_types {
 		if concrete_type.has_flag(.generic) {
-			has_generic = true
 			concrete_types << c.unwrap_generic(concrete_type)
 		} else {
 			concrete_types << concrete_type
 		}
 	}
-	if has_generic {
+	if concrete_types.len > 0 {
 		if c.table.register_fn_concrete_types(node.name, concrete_types) {
 			c.need_recheck_generic_fns = true
 		}
@@ -2539,13 +2537,17 @@ pub fn (mut c Checker) fn_call(mut node ast.CallExpr, mut continue_check &bool)
 		c.error('generic fn using generic types cannot be called outside of generic fn',
 			node.pos)
 	}
-	if has_generic {
+	if concrete_types.len > 0 {
 		mut no_exists := true
-		if c.mod != '' && !fn_name.contains('.') {
+		if fn_name.contains('.') {
-			// Need to prepend the module when adding a generic type to a function
-			no_exists = c.table.register_fn_concrete_types(c.mod + '.' + fn_name, concrete_types)
-		} else {
 			no_exists = c.table.register_fn_concrete_types(fn_name, concrete_types)
+		} else {
+			no_exists = c.table.register_fn_concrete_types(c.mod + '.' + fn_name, concrete_types)
+			// if the generic fn does not exist in the current fn calling module, continue
+			// to look in builtin module
+			if !no_exists {
+				no_exists = c.table.register_fn_concrete_types(fn_name, concrete_types)
+			}
 		}
 		if no_exists {
 			c.need_recheck_generic_fns = true

vlib/v/parser/fn.v

@@ -40,14 +40,6 @@ pub fn (mut p Parser) call_expr(language ast.Language, mod string) ast.CallExpr
 		p.expr_mod = ''
 		concrete_types = p.parse_concrete_types()
 		concrete_list_pos = concrete_list_pos.extend(p.prev_tok.position())
-		// In case of `foo<T>()`
-		// T is unwrapped and registered in the checker.
-		full_generic_fn_name := if fn_name.contains('.') { fn_name } else { p.prepend_mod(fn_name) }
-		has_generic := concrete_types.any(it.has_flag(.generic))
-		if !has_generic {
-			// will be added in checker
-			p.table.register_fn_concrete_types(full_generic_fn_name, concrete_types)
-		}
 	}
 	p.check(.lpar)
 	args := p.call_args()
@@ -528,6 +520,9 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 		scope: p.scope
 		label_names: p.label_names
 	}
+	if generic_names.len > 0 {
+		p.table.register_fn_generic_types(name)
+	}
 	p.label_names = []
 	p.close_scope()
 	return fn_decl