test: add tests and snapshots

Author: ankddev

compiler-core/src/type_/tests/snapshots/gleam_core__type___tests__warnings__prefer_list_is_empty_over_0_lt_list_length.snap

@@ -0,0 +1,30 @@
+---
+source: compiler-core/src/type_/tests/warnings.rs
+expression: "\n        import gleam/list\n\n        pub fn main() {\n            let a_list = []\n            let _ = 0 < list.length(a_list)\n        }\n        "
+---
+----- SOURCE CODE
+-- gleam/list.gleam
+pub fn length(_list: List(a)) -> Int { 0 }
+
+-- main.gleam
+
+        import gleam/list
+
+        pub fn main() {
+            let a_list = []
+            let _ = 0 < list.length(a_list)
+        }
+        
+
+----- WARNING
+warning: Inefficient use of `list.length`
+  ┌─ /src/warning/wrn.gleam:6:21
+  │
+6 │             let _ = 0 < list.length(a_list)
+  │                     ^^^^^^^^^^^^^^^^^^^^^^^
+
+The `list.length` function has to iterate across the whole
+list to calculate the length, which is wasteful if you only
+need to know if the list is empty or not.
+
+Hint: You can use `the_list != []` instead.

compiler-core/src/type_/tests/snapshots/gleam_core__type___tests__warnings__prefer_list_is_empty_over_list_length_gt_0.snap

@@ -0,0 +1,30 @@
+---
+source: compiler-core/src/type_/tests/warnings.rs
+expression: "\n        import gleam/list\n\n        pub fn main() {\n            let a_list = []\n            let _ = list.length(a_list) > 0\n        }\n        "
+---
+----- SOURCE CODE
+-- gleam/list.gleam
+pub fn length(_list: List(a)) -> Int { 0 }
+
+-- main.gleam
+
+        import gleam/list
+
+        pub fn main() {
+            let a_list = []
+            let _ = list.length(a_list) > 0
+        }
+        
+
+----- WARNING
+warning: Inefficient use of `list.length`
+  ┌─ /src/warning/wrn.gleam:6:21
+  │
+6 │             let _ = list.length(a_list) > 0
+  │                     ^^^^^^^^^^^^^^^^^^^^^^^
+
+The `list.length` function has to iterate across the whole
+list to calculate the length, which is wasteful if you only
+need to know if the list is empty or not.
+
+Hint: You can use `the_list != []` instead.

compiler-core/src/type_/tests/snapshots/gleam_core__type___tests__warnings__prefer_list_is_empty_over_list_length_gt_negative_0.snap

@@ -0,0 +1,30 @@
+---
+source: compiler-core/src/type_/tests/warnings.rs
+expression: "\n        import gleam/list\n\n        pub fn main() {\n            let a_list = []\n            let _ = list.length(a_list) > 0\n        }\n        "
+---
+----- SOURCE CODE
+-- gleam/list.gleam
+pub fn length(_list: List(a)) -> Int { 0 }
+
+-- main.gleam
+
+        import gleam/list
+
+        pub fn main() {
+            let a_list = []
+            let _ = list.length(a_list) > 0
+        }
+        
+
+----- WARNING
+warning: Inefficient use of `list.length`
+  ┌─ /src/warning/wrn.gleam:6:21
+  │
+6 │             let _ = list.length(a_list) > 0
+  │                     ^^^^^^^^^^^^^^^^^^^^^^^
+
+The `list.length` function has to iterate across the whole
+list to calculate the length, which is wasteful if you only
+need to know if the list is empty or not.
+
+Hint: You can use `the_list != []` instead.

compiler-core/src/type_/tests/snapshots/gleam_core__type___tests__warnings__prefer_list_is_empty_over_negative_0_lt_list_length.snap

@@ -0,0 +1,30 @@
+---
+source: compiler-core/src/type_/tests/warnings.rs
+expression: "\n        import gleam/list\n\n        pub fn main() {\n            let a_list = []\n            let _ = 0 < list.length(a_list)\n        }\n        "
+---
+----- SOURCE CODE
+-- gleam/list.gleam
+pub fn length(_list: List(a)) -> Int { 0 }
+
+-- main.gleam
+
+        import gleam/list
+
+        pub fn main() {
+            let a_list = []
+            let _ = 0 < list.length(a_list)
+        }
+        
+
+----- WARNING
+warning: Inefficient use of `list.length`
+  ┌─ /src/warning/wrn.gleam:6:21
+  │
+6 │             let _ = 0 < list.length(a_list)
+  │                     ^^^^^^^^^^^^^^^^^^^^^^^
+
+The `list.length` function has to iterate across the whole
+list to calculate the length, which is wasteful if you only
+need to know if the list is empty or not.
+
+Hint: You can use `the_list != []` instead.

compiler-core/src/type_/tests/warnings.rs

@@ -678,6 +678,86 @@ fn prefer_list_is_empty_over_list_length_lt_1() {
     );
 }
 
+/// https://github.com/gleam-lang/gleam/issues/4861
+#[test]
+fn prefer_list_is_empty_over_list_length_gt_negative_0() {
+    assert_warning!(
+        (
+            "gleam_stdlib",
+            "gleam/list",
+            "pub fn length(_list: List(a)) -> Int { 0 }"
+        ),
+        r#"
+        import gleam/list
+
+        pub fn main() {
+            let a_list = []
+            let _ = list.length(a_list) > 0
+        }
+        "#
+    );
+}
+
+/// https://github.com/gleam-lang/gleam/issues/4861
+#[test]
+fn prefer_list_is_empty_over_negative_0_lt_list_length() {
+    assert_warning!(
+        (
+            "gleam_stdlib",
+            "gleam/list",
+            "pub fn length(_list: List(a)) -> Int { 0 }"
+        ),
+        r#"
+        import gleam/list
+
+        pub fn main() {
+            let a_list = []
+            let _ = 0 < list.length(a_list)
+        }
+        "#
+    );
+}
+
+/// https://github.com/gleam-lang/gleam/issues/4861
+#[test]
+fn prefer_list_is_empty_over_list_length_gt_0() {
+    assert_warning!(
+        (
+            "gleam_stdlib",
+            "gleam/list",
+            "pub fn length(_list: List(a)) -> Int { 0 }"
+        ),
+        r#"
+        import gleam/list
+
+        pub fn main() {
+            let a_list = []
+            let _ = list.length(a_list) > 0
+        }
+        "#
+    );
+}
+
+/// https://github.com/gleam-lang/gleam/issues/4861
+#[test]
+fn prefer_list_is_empty_over_0_lt_list_length() {
+    assert_warning!(
+        (
+            "gleam_stdlib",
+            "gleam/list",
+            "pub fn length(_list: List(a)) -> Int { 0 }"
+        ),
+        r#"
+        import gleam/list
+
+        pub fn main() {
+            let a_list = []
+            let _ = 0 < list.length(a_list)
+        }
+        "#
+    );
+}
+
 /// https://github.com/gleam-lang/gleam/issues/2067
 #[test]
 fn allow_list_length_eq_1() {