Rollup merge of #139705 - jieyouxu:tests-precursor, r=compiler-errors

Removed outdated ui test suite README, give reasons for disabled tests

### Changes

- `tests/ui/README.md` is very outdated, test suite docs should consistently live in rustc-dev-guide.
- Add reasons for `//@ ignore-test` tests that don't have one.[^query]

This is a precursor change to make follow-up changes easier (possibly more specialized directives or converting some auxiliaries into the canonical `auxiliary/` form).

[^query]: searched via `rg --no-ignore -F -e "ignore-test" tests/`.

tests/ui/README.md

@@ -1,35 +0,0 @@
-# UI Tests
-
-This folder contains `rustc`'s
-[UI tests](https://rustc-dev-guide.rust-lang.org/tests/ui.html).
-
-## Test Directives (Headers)
-
-Typically, a UI test will have some test directives / headers which are
-special comments that tell compiletest how to build and interpret a test.
-
-As part of an ongoing effort to rewrite compiletest
-(see <https://github.com/rust-lang/compiler-team/issues/536>), a major
-change proposal to change legacy compiletest-style headers `// <directive>`
-to [`ui_test`](https://github.com/oli-obk/ui_test)-style headers
-`//@ <directive>` was accepted (see
-<https://github.com/rust-lang/compiler-team/issues/512>.
-
-An example directive is `ignore-test`. In legacy compiletest style, the header
-would be written as
-
-```rs
-// ignore-test
-```
-
-but in `ui_test` style, the header would be written as
-
-```rs
-//@ ignore-test
-```
-
-compiletest is changed to accept only `//@` directives for UI tests
-(currently), and will reject and report an error if it encounters any
-comments `// <content>` that may be parsed as a legacy compiletest-style
-test header. To fix this, you should migrate to the `ui_test`-style header
-`//@ <content>`.

tests/ui/bootstrap/self-test/a.rs

@@ -1,2 +1,2 @@
 //! Not used by compiler, this is used by bootstrap cli self-test.
-//@ ignore-test
+//@ ignore-test (used by bootstrap)

tests/ui/bootstrap/self-test/b.rs

@@ -1,2 +1,2 @@
 //! Not used by compiler, used by bootstrap cli self-test.
-//@ ignore-test
+//@ ignore-test (used by bootstrap)

tests/ui/lint/unknown-lints/other.rs

@@ -1,4 +1,4 @@
-//@ ignore-test
+//@ ignore-test (auxiliary)
 
 // Companion to allow-in-other-module.rs
 

tests/ui/precondition-checks/read.rs

@@ -2,7 +2,7 @@
 //@ compile-flags: -Copt-level=3 -Cdebug-assertions=no -Zub-checks=yes
 //@ error-pattern: unsafe precondition(s) violated: ptr::read requires
 //@ revisions: null misaligned
-//@ ignore-test
+//@ ignore-test (unimplemented)
 
 use std::ptr;
 

tests/ui/precondition-checks/write.rs

@@ -2,7 +2,7 @@
 //@ compile-flags: -Copt-level=3 -Cdebug-assertions=no -Zub-checks=yes
 //@ error-pattern: unsafe precondition(s) violated: ptr::write requires
 //@ revisions: null misaligned
-//@ ignore-test
+//@ ignore-test (unimplemented)
 
 use std::ptr;
 

tests/ui/precondition-checks/write_bytes.rs

@@ -2,7 +2,7 @@
 //@ compile-flags: -Copt-level=3 -Cdebug-assertions=no -Zub-checks=yes
 //@ error-pattern: unsafe precondition(s) violated: ptr::write requires
 //@ revisions: null misaligned
-//@ ignore-test
+//@ ignore-test (unimplemented)
 
 use std::ptr;
 

tests/ui/traits/next-solver/object-soundness-requires-generalization.rs

@@ -1,5 +1,5 @@
 //@ compile-flags: -Znext-solver
-//@ ignore-test
+//@ ignore-test (see #114196)
 
 trait Trait {
     type Gat<'lt>;