ast,checker,cgen: fix generics function with embedded structs, ensure correct link generation in cgen (#20900)

vlib/v/ast/ast.v

@@ -290,6 +290,7 @@ pub mut:
 	gkind_field              GenericKindField // `T.name` => ast.GenericKindField.name, `T.typ` => ast.GenericKindField.typ, or .unknown
 	scope                    &Scope = unsafe { nil }
 	from_embed_types         []Type   // holds the type of the embed that the method is called from
+	generic_from_embed_types [][]Type // holds the types of the embeds for each generic instance when the same generic method is called.
 	has_hidden_receiver      bool
 }
 

vlib/v/checker/checker.v

@@ -1583,6 +1583,7 @@ fn (mut c Checker) selector_expr(mut node ast.SelectorExpr) ast.Type {
 					ast.StructField{}, []ast.Type{}
 				}
 				node.from_embed_types = embed_types
+				node.generic_from_embed_types << embed_types
 			}
 		}
 	}

vlib/v/gen/c/cgen.v

@@ -3889,20 +3889,26 @@ fn (mut g Gen) selector_expr(node ast.SelectorExpr) {
 	}
 	// struct embedding
 	if sym.info in [ast.Struct, ast.Aggregate] {
-		for i, embed in node.from_embed_types {
-			embed_sym := g.table.sym(embed)
-			embed_name := embed_sym.embed_name()
-			is_left_ptr := if i == 0 {
-				node.expr_type.is_ptr()
-			} else {
-				node.from_embed_types[i - 1].is_ptr()
+		if node.generic_from_embed_types.len > 0 && sym.info is ast.Struct {
+			if sym.info.embeds.len > 0 {
+				mut is_find := false
+				for arr_val in node.generic_from_embed_types {
+					if arr_val.len > 0 {
+						if arr_val[0] == sym.info.embeds[0] {
+							g.write_selector_expr_embed_name(node, arr_val)
+							is_find = true
+							break
 						}
-			if is_left_ptr {
-				g.write('->')
-			} else {
-				g.write('.')
 					}
-			g.write(embed_name)
+				}
+				if !is_find {
+					g.write_selector_expr_embed_name(node, node.from_embed_types)
+				}
+			} else {
+				g.write_selector_expr_embed_name(node, node.from_embed_types)
+			}
+		} else {
+			g.write_selector_expr_embed_name(node, node.from_embed_types)
 		}
 	}
 	alias_to_ptr := sym.info is ast.Alias && sym.info.parent_type.is_ptr()
@@ -3928,6 +3934,24 @@ fn (mut g Gen) selector_expr(node ast.SelectorExpr) {
 	}
 }
 
+fn (mut g Gen) write_selector_expr_embed_name(node ast.SelectorExpr, embed_types []ast.Type) {
+	for i, embed in embed_types {
+		embed_sym := g.table.sym(embed)
+		embed_name := embed_sym.embed_name()
+		is_left_ptr := if i == 0 {
+			node.expr_type.is_ptr()
+		} else {
+			embed_types[i - 1].is_ptr()
+		}
+		if is_left_ptr {
+			g.write('->')
+		} else {
+			g.write('.')
+		}
+		g.write(embed_name)
+	}
+}
+
 // check_var_scope checks if the variable has its value known from the node position
 @[inline]
 fn (mut g Gen) check_var_scope(obj ast.Var, node_pos int) bool {

vlib/v/tests/generics_method_with_embedded_structs_test.v

@@ -0,0 +1,46 @@
+struct Base {
+	i int
+}
+
+struct Base1 {
+	Base
+}
+
+struct Base2 {
+	Base
+}
+
+struct Struct1 {
+	Base1
+}
+
+struct Struct1O {
+	Struct1
+}
+
+struct Struct2 {
+	Base2
+}
+
+struct Struct2O {
+	Struct2
+}
+
+fn (b &Base) func[T]() T {
+	t := T{
+		i: b.i
+	}
+	if t.i == 0 {
+	}
+	return t
+}
+
+fn test_generic_fn_with_embedded_structs() {
+	s1 := Struct1{}
+	s2 := Struct2{}
+	res1 := s1.func[Struct1O]()
+	res2 := s2.func[Struct2O]()
+
+	assert res1.i == 0
+	assert res2.i == 0
+}