add uitest for indexing in unnecessary const items

Author: tesuji

tests/ui/unnecessary_operation.fixed

@@ -43,7 +43,7 @@ fn get_number() -> i32 {
     0
 }
 
-fn get_usize() -> usize {
+const fn get_usize() -> usize {
     0
 }
 fn get_struct() -> Struct {
@@ -113,4 +113,15 @@ fn main() {
     'label: {
         break 'label
     };
+    let () = const {
+        assert!([42, 55].len() > get_usize());
+    };
+}
+
+const _: () = {
+    assert!([42, 55].len() > get_usize());
+};
+
+const fn foo() {
+    assert!([42, 55].len() > get_usize());
 }

tests/ui/unnecessary_operation.rs

@@ -43,7 +43,7 @@ fn get_number() -> i32 {
     0
 }
 
-fn get_usize() -> usize {
+const fn get_usize() -> usize {
     0
 }
 fn get_struct() -> Struct {
@@ -117,4 +117,15 @@ fn main() {
     'label: {
         break 'label
     };
+    let () = const {
+        [42, 55][get_usize()];
+    };
+}
+
+const _: () = {
+    [42, 55][get_usize()];
+};
+
+const fn foo() {
+    [42, 55][get_usize()];
 }

tests/ui/unnecessary_operation.stderr

@@ -119,5 +119,23 @@ LL | |         s: String::from("blah"),
 LL | |     };
    | |______^ help: statement can be reduced to: `String::from("blah");`
 
-error: aborting due to 19 previous errors
+error: unnecessary operation
+  --> tests/ui/unnecessary_operation.rs:121:9
+   |
+LL |         [42, 55][get_usize()];
+   |         ^^^^^^^^^^^^^^^^^^^^^^ help: statement can be written as: `assert!([42, 55].len() > get_usize());`
+
+error: unnecessary operation
+  --> tests/ui/unnecessary_operation.rs:126:5
+   |
+LL |     [42, 55][get_usize()];
+   |     ^^^^^^^^^^^^^^^^^^^^^^ help: statement can be written as: `assert!([42, 55].len() > get_usize());`
+
+error: unnecessary operation
+  --> tests/ui/unnecessary_operation.rs:130:5
+   |
+LL |     [42, 55][get_usize()];
+   |     ^^^^^^^^^^^^^^^^^^^^^^ help: statement can be written as: `assert!([42, 55].len() > get_usize());`
+
+error: aborting due to 22 previous errors