cleaned up some tests

Author: Kivooeo

tests/ui/empty-allocation-non-null.rs renamed to tests/ui/allocator/empty-alloc-nonnull-guarantee.rs

@@ -1,3 +1,7 @@
+//! Check that the default global Rust allocator produces non-null Box allocations for ZSTs.
+//!     
+//! See https://github.com/rust-lang/rust/issues/11998
+
 //@ run-pass
 
 pub fn main() {

tests/ui/diverging-fn-tail-35849.rs

@@ -0,0 +1,19 @@
+//! Test early return within binary operation expressions
+
+//@ run-pass
+
+#![allow(dead_code)]
+#![allow(unreachable_code)]
+
+use std::ops::Add;
+
+/// Function that performs addition with an early return in the right operand
+fn add_with_early_return<T: Add<Output = T> + Copy>(n: T) -> T {
+    n + { return n }
+}
+
+pub fn main() {
+    // Test with different numeric types to ensure generic behavior works
+    let _result1 = add_with_early_return(42i32);
+    let _result2 = add_with_early_return(3.14f64);
+}

tests/ui/early-ret-binop-add.rs

@@ -1,3 +1,5 @@
+//! Test that duplicate use bindings in same namespace produce error
+
 mod foo {
     pub use self::bar::X;
     use self::bar::X;

tests/ui/elide-errors-on-mismatched-tuple.rs

@@ -1,5 +1,5 @@
 error[E0252]: the name `X` is defined multiple times
-  --> $DIR/double-type-import.rs:3:9
+  --> $DIR/duplicate-use-bindings.rs:5:9
    |
 LL |     pub use self::bar::X;
    |             ------------ previous import of the type `X` here