Rollup merge of #121527 - Enselic:unix_sigpipe-tests-fixes, r=davidtwco

unix_sigpipe: Simple fixes and improvements in tests

In #120832 I included 5 preparatory commits.

It will take a while before discussions there and in #62569 is settled, so here is a PR that splits out 4 of the commits that are easy to review, to get them out of the way.

r? ``@davidtwco`` who already approved these commits in #120832 (but I have tweaked them a bit and rebased them since then).

For the convenience of my reviewer, here are the full commit messages of the commits:
<details>
<summary>Click to expand</summary>

```
commit 948b1d6 (HEAD -> unix_sigpipe-tests-fixes, origin/unix_sigpipe-tests-fixes)
Author: Martin Nordholts <martin.nordholts@codetale.se>
Date:   Fri Feb 9 07:57:27 2024 +0100

    tests: Add unix_sigpipe-different-duplicates.rs test variant

    To make sure that

        #[unix_sigpipe = "x"]
        #[unix_sigpipe = "y"]

    behaves like

        #[unix_sigpipe = "x"]
        #[unix_sigpipe = "x"]

commit d14f158
Author: Martin Nordholts <martin.nordholts@codetale.se>
Date:   Fri Feb 9 08:47:47 2024 +0100

    tests: Combine unix_sigpipe-not-used.rs and unix_sigpipe-only-feature.rs

    The only difference between the files is the presence/absence of

        #![feature(unix_sigpipe)]

    attribute. Avoid duplication by using revisions instead.

commit a1cb3db
Author: Martin Nordholts <martin.nordholts@codetale.se>
Date:   Fri Feb 9 06:44:56 2024 +0100

    tests: Rename unix_sigpipe.rs to unix_sigpipe-bare.rs for clarity

    The test is for the "bare" variant of the attribute that looks like this:

        #[unix_sigpipe]

    which is not allowed, because it must look like this:

        #[unix_sigpipe = "sig_ign"]

commit e060274
Author: Martin Nordholts <martin.nordholts@codetale.se>
Date:   Fri Feb 9 05:48:24 2024 +0100

    tests: Fix typo unix_sigpipe-error.rs -> unix_sigpipe-sig_ign.rs

    There is no error expected. It's simply the "regular" test for sig_ign.
    So rename it.
```

</details>

Tracking issue: #97889

tests/ui/attributes/unix_sigpipe/unix_sigpipe.stderr → tests/ui/attributes/unix_sigpipe/unix_sigpipe-bare.stderr

@@ -1,5 +1,5 @@
 error: valid values for `#[unix_sigpipe = "..."]` are `inherit`, `sig_ign`, or `sig_dfl`
-  --> $DIR/unix_sigpipe.rs:3:1
+  --> $DIR/unix_sigpipe-bare.rs:3:1
    |
 LL | #[unix_sigpipe]
    | ^^^^^^^^^^^^^^^

tests/ui/attributes/unix_sigpipe/unix_sigpipe-different-duplicates.rs

@@ -0,0 +1,5 @@
+#![feature(unix_sigpipe)]
+
+#[unix_sigpipe = "sig_ign"]
+#[unix_sigpipe = "inherit"] //~ error: multiple `unix_sigpipe` attributes
+fn main() {}

tests/ui/attributes/unix_sigpipe/unix_sigpipe-different-duplicates.stderr

@@ -0,0 +1,14 @@
+error: multiple `unix_sigpipe` attributes
+  --> $DIR/unix_sigpipe-different-duplicates.rs:4:1
+   |
+LL | #[unix_sigpipe = "inherit"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unix_sigpipe-different-duplicates.rs:3:1
+   |
+LL | #[unix_sigpipe = "sig_ign"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+

tests/ui/attributes/unix_sigpipe/unix_sigpipe-duplicates.rs

@@ -1,5 +1,5 @@
 #![feature(unix_sigpipe)]
 
-#[unix_sigpipe = "sig_ign"]
+#[unix_sigpipe = "inherit"]
 #[unix_sigpipe = "inherit"] //~ error: multiple `unix_sigpipe` attributes
 fn main() {}

tests/ui/attributes/unix_sigpipe/unix_sigpipe-duplicates.stderr

@@ -7,7 +7,7 @@ LL | #[unix_sigpipe = "inherit"]
 note: attribute also specified here
   --> $DIR/unix_sigpipe-duplicates.rs:3:1
    |
-LL | #[unix_sigpipe = "sig_ign"]
+LL | #[unix_sigpipe = "inherit"]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error

tests/ui/attributes/unix_sigpipe/unix_sigpipe-not-used.rs

@@ -1,6 +1,9 @@
+//@ revisions: with_feature without_feature
 //@ run-pass
 //@ aux-build:sigpipe-utils.rs
 
+#![cfg_attr(with_feature, feature(unix_sigpipe))]
+
 fn main() {
     extern crate sigpipe_utils;