Use rmake diff output in test

tests/run-make/crate-loading-crate-depends-on-itself/foo.stderr

@@ -0,0 +1,34 @@
+error[E0277]: the trait bound `foo::Struct: Trait` is not satisfied
+  --> foo-current.rs:13:19
+   |
+13 |     check_trait::<foo::Struct>();
+   |                   ^^^^^^^^^^^ the trait `Trait` is not implemented for `foo::Struct`
+   |
+note: there are multiple different versions of crate `foo` in the dependency graph
+  --> foo-current.rs:7:1
+   |
+4  | extern crate foo;
+   | ----------------- one version of crate `foo` is used here, as a direct dependency of the current crate
+5  |
+6  | pub struct Struct;
+   | ----------------- this type implements the required trait
+7  | pub trait Trait {}
+   | ^^^^^^^^^^^^^^^ this is the required trait
+   |
+  ::: foo-prev.rs:X:Y
+   |
+4  | pub struct Struct;
+   | ----------------- this type doesn't implement the required trait
+5  | pub trait Trait {}
+   | --------------- this is the found trait
+   = note: two types coming from two different versions of the same crate are different types even if they look the same
+   = help: you can use `cargo tree` to explore your dependency tree
+note: required by a bound in `check_trait`
+  --> foo-current.rs:10:19
+   |
+10 | fn check_trait<T: Trait>() {}
+   |                   ^^^^^ required by this bound in `check_trait`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/run-make/crate-loading-crate-depends-on-itself/rmake.rs

@@ -7,26 +7,25 @@
 // and traits of the different versions are mixed, we produce diagnostic output and not an ICE.
 // #133563
 
-use run_make_support::{rust_lib_name, rustc};
+use run_make_support::{diff, rust_lib_name, rustc};
 
 fn main() {
     rustc().input("foo-prev.rs").run();
 
-    rustc()
+    let out = rustc()
         .extra_filename("current")
         .metadata("current")
         .input("foo-current.rs")
         .extern_("foo", rust_lib_name("foo"))
         .run_fail()
-        .assert_stderr_contains(r#"
+        .stderr_utf8();
-note: there are multiple different versions of crate `foo` in the dependency graph
+
-  --> foo-current.rs:7:1
+    // We don't remap the path of the `foo-prev` crate, so we remap it here.
-   |
+    let mut lines: Vec<_> = out.lines().collect();
-4  | extern crate foo;
+    for line in &mut lines {
-   | ----------------- one version of crate `foo` is used here, as a direct dependency of the current crate
+        if line.starts_with("  ::: ") {
-5  |
+            *line = "  ::: foo-prev.rs:X:Y";
-6  | pub struct Struct;
+        }
-   | ----------------- this type implements the required trait
+    }
-7  | pub trait Trait {}
+    diff().expected_file("foo.stderr").actual_text("(rustc)", &lines.join("\n")).run();
-   | ^^^^^^^^^^^^^^^ this is the required trait"#);
 }