checker: fix type inference, when pushing an empty array to a 2D array (fix #23854) (#25508)

StunxFS · web-flow · commit 3dfd06be79fe · 2025-10-22T14:28:32.000+03:00
diff --git a/vlib/v/checker/infix.v b/vlib/v/checker/infix.v
@@ -71,6 +71,13 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 					}
 				}
 			}
+		} else if mut node.right is ast.ArrayInit {
+			if node.right.exprs.len == 0 && node.right.elem_type == ast.void_type {
+				// handle arr << [] where [] is empty
+				info := c.table.sym(left_type).array_info()
+				node.right.elem_type = info.elem_type
+				c.expected_type = info.elem_type
+			}
 		}
 	}
 	mut right_type := c.expr(mut node.right)
diff --git a/vlib/v/tests/builtin_arrays/array_2d_append_empty_array_test.v b/vlib/v/tests/builtin_arrays/array_2d_append_empty_array_test.v
@@ -0,0 +1,7 @@
+fn test_array_2d_append_empty_array() {
+	mut b := [][]int{}
+	b << [1, 2, 3]
+	b << []
+	assert b[0][0] == 1
+	assert b[1] == []
+}

Original file line number	Diff line number	Diff line change
`@@ -71,6 +71,13 @@ fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {`
`71`	`71`	`}`
`72`	`72`	`}`
`73`	`73`	`}`
	`74`	`+ } else if mut node.right is ast.ArrayInit {`
	`75`	`+ if node.right.exprs.len == 0 && node.right.elem_type == ast.void_type {`
	`76`	`+ // handle arr << [] where [] is empty`
	`77`	`+ info := c.table.sym(left_type).array_info()`
	`78`	`+ node.right.elem_type = info.elem_type`
	`79`	`+ c.expected_type = info.elem_type`
	`80`	`+ }`
`74`	`81`	`}`
`75`	`82`	`}`
`76`	`83`	`mut right_type := c.expr(mut node.right)`