checker: add error for struct not init (fix #24893) (#25134)

vlib/v/checker/checker.v

@@ -4377,8 +4377,10 @@ fn (mut c Checker) ident(mut node ast.Ident) ast.Type {
 						}
 					}
 				}
-				c.error(util.new_suggestion(node.name, const_names_in_mod).say('undefined ident: `${node.name}`'),
-					node.pos)
+				c.check_known_struct_name(node) or {
+					c.error(util.new_suggestion(node.name, const_names_in_mod).say('undefined ident: `${node.name}`'),
+						node.pos)
+				}
 			} else {
 				// If a variable is not found in the scope of an anonymous function
 				// but is in an external scope, then we can suggest the user add it to the capturing list.
@@ -4398,13 +4400,32 @@ fn (mut c Checker) ident(mut node ast.Ident) ast.Type {
 					}
 				}
 
-				c.error('undefined ident: `${node.name}`', node.pos)
+				c.check_known_struct_name(node) or {
+					c.error('undefined ident: `${node.name}`', node.pos)
+				}
 			}
 		}
 	}
 	return ast.void_type
 }
 
+fn (mut c Checker) check_known_struct_name(ident ast.Ident) ? {
+	mut is_struct := false
+	if ident.mod == 'builtin' || ident.mod == 'main' {
+		is_struct = c.table.find_type(ident.name) != 0
+		if !is_struct {
+			is_struct = c.table.find_type('main.${ident.name}') != 0
+		}
+	} else {
+		is_struct = c.table.find_type('${ident.mod}.${ident.name}') != 0
+	}
+	if is_struct {
+		c.error('`${ident.name}` must be initialized', ident.pos)
+		return
+	}
+	return none
+}
+
 fn (mut c Checker) concat_expr(mut node ast.ConcatExpr) ast.Type {
 	mut mr_types := []ast.Type{}
 	for mut expr in node.vals {

vlib/v/checker/tests/globals/assign_no_value.out

@@ -1,5 +1,5 @@
-vlib/v/checker/tests/globals/assign_no_value.vv:2:9: error: undefined ident: `int`
+vlib/v/checker/tests/globals/assign_no_value.vv:2:9: error: undefined ident: `int_i`
     1 | __global (
-    2 |     test = int
-      |            ~~~
+    2 |     test = int_i
+      |            ~~~~~
     3 | )

vlib/v/checker/tests/globals/assign_no_value.vv

@@ -1,3 +1,3 @@
 __global (
-	test = int
+	test = int_i
 )

vlib/v/checker/tests/match_undefined_cond.out

@@ -1,21 +1,20 @@
-vlib/v/checker/tests/match_undefined_cond.vv:4:15: error: undefined ident: `Asd`
-    2 | 
-    3 | fn main() {
-    4 |     res := match Asd {
+vlib/v/checker/tests/match_undefined_cond.vv:2:15: error: undefined ident: `asd`
+    1 | fn main() {
+    2 |     res := match asd {
       |                  ~~~
-    5 |         1 { 'foo' }
-    6 |         2 { 'test' }
-vlib/v/checker/tests/match_undefined_cond.vv:5:3: error: cannot match `void` with `int literal`
-    3 | fn main() {
-    4 |     res := match Asd {
-    5 |         1 { 'foo' }
+    3 |         1 { 'foo' }
+    4 |         2 { 'test' }
+vlib/v/checker/tests/match_undefined_cond.vv:3:3: error: cannot match `void` with `int literal`
+    1 | fn main() {
+    2 |     res := match asd {
+    3 |         1 { 'foo' }
       |         ^
-    6 |         2 { 'test' }
-    7 |         else { '' }
-vlib/v/checker/tests/match_undefined_cond.vv:6:3: error: cannot match `void` with `int literal`
-    4 |     res := match Asd {
-    5 |         1 { 'foo' }
-    6 |         2 { 'test' }
+    4 |         2 { 'test' }
+    5 |         else { '' }
+vlib/v/checker/tests/match_undefined_cond.vv:4:3: error: cannot match `void` with `int literal`
+    2 |     res := match asd {
+    3 |         1 { 'foo' }
+    4 |         2 { 'test' }
       |         ^
-    7 |         else { '' }
-    8 |     }
+    5 |         else { '' }
+    6 |     }

vlib/v/checker/tests/match_undefined_cond.vv

@@ -1,7 +1,5 @@
-type Asd = int
-
 fn main() {
-	res := match Asd {
+	res := match asd {
 		1 { 'foo' }
 		2 { 'test' }
 		else { '' }

vlib/v/checker/tests/struct_not_init_err.out

@@ -0,0 +1,21 @@
+vlib/v/checker/tests/struct_not_init_err.vv:11:7: error: `Data` must be initialized
+    9 |
+   10 | fn main() {
+   11 |     _ := Data
+      |          ~~~~
+   12 |     _ := DataCollection
+   13 |     _ := ast.Type
+vlib/v/checker/tests/struct_not_init_err.vv:12:7: error: `DataCollection` must be initialized
+   10 | fn main() {
+   11 |     _ := Data
+   12 |     _ := DataCollection
+      |          ~~~~~~~~~~~~~~
+   13 |     _ := ast.Type
+   14 |     // _ := gui.Animate // for vpm mod
+vlib/v/checker/tests/struct_not_init_err.vv:13:11: error: `v.ast.Type` must be initialized
+   11 |     _ := Data
+   12 |     _ := DataCollection
+   13 |     _ := ast.Type
+      |              ~~~~
+   14 |     // _ := gui.Animate // for vpm mod
+   15 | }

vlib/v/checker/tests/struct_not_init_err.vv

@@ -0,0 +1,15 @@
+module main
+
+import v.ast
+
+struct Data {
+}
+
+type DataCollection = Data
+
+fn main() {
+	_ := Data
+	_ := DataCollection
+	_ := ast.Type
+	// _ := gui.Animate // for vpm mod
+}