Add "reference" as a known compiletest header

This adds the "reference" compiletest header so that the Rust reference
can add annotations to the test suite in order to link tests to
individual rules in the reference.

Tooling in the reference repo will be responsible for collecting these
annotations and linking to the tests.

More details are in MCP 783: rust-lang/compiler-team#783

Author: ehuss

src/tools/compiletest/src/command-list.rs

@@ -208,6 +208,7 @@ const KNOWN_DIRECTIVE_NAMES: &[&str] = &[
     "pretty-compare-only",
     "pretty-expanded",
     "pretty-mode",
+    "reference",
     "regex-error-pattern",
     "remap-src-base",
     "revisions",

tests/run-make/include-all-symbols-linking/rmake.rs

@@ -1,6 +1,6 @@
 // Linkers treat archives differently from object files: all object files participate in linking,
-// while archives will only participate in linking if they can satisfy at least one undefined
-// reference (version scripts doesn't count). This causes `#[no_mangle]` or `#[used]` items to
+// while archives will only participate in linking if they can satisfy at least one undefined reference
+// (version scripts doesn't count). This causes `#[no_mangle]` or `#[used]` items to
 // be ignored by the linker, and since they never participate in the linking, using `KEEP` in the
 // linker scripts can't keep them either. This causes #47384. After the fix in #95604, this test
 // checks that these symbols and sections successfully appear in the output dynamic library.

tests/ui/destructure-trait-ref.rs

@@ -1,5 +1,4 @@
-// The regression test for #15031 to make sure destructuring trait
-// reference work properly.
+// The regression test for #15031 to make sure destructuring trait reference work properly.
 
 #![feature(box_patterns)]
 

tests/ui/destructure-trait-ref.stderr

@@ -1,23 +1,23 @@
 error[E0033]: type `&dyn T` cannot be dereferenced
-  --> $DIR/destructure-trait-ref.rs:26:9
+  --> $DIR/destructure-trait-ref.rs:25:9
    |
 LL |     let &x = &1isize as &dyn T;
    |         ^^ type `&dyn T` cannot be dereferenced
 
 error[E0033]: type `&dyn T` cannot be dereferenced
-  --> $DIR/destructure-trait-ref.rs:27:10
+  --> $DIR/destructure-trait-ref.rs:26:10
    |
 LL |     let &&x = &(&1isize as &dyn T);
    |          ^^ type `&dyn T` cannot be dereferenced
 
 error[E0033]: type `Box<dyn T>` cannot be dereferenced
-  --> $DIR/destructure-trait-ref.rs:28:9
+  --> $DIR/destructure-trait-ref.rs:27:9
    |
 LL |     let box x = Box::new(1isize) as Box<dyn T>;
    |         ^^^^^ type `Box<dyn T>` cannot be dereferenced
 
 error[E0308]: mismatched types
-  --> $DIR/destructure-trait-ref.rs:32:10
+  --> $DIR/destructure-trait-ref.rs:31:10
    |
 LL |     let &&x = &1isize as &dyn T;
    |          ^^   ----------------- this expression has type `&dyn T`
@@ -33,7 +33,7 @@ LL +     let &x = &1isize as &dyn T;
    |
 
 error[E0308]: mismatched types
-  --> $DIR/destructure-trait-ref.rs:36:11
+  --> $DIR/destructure-trait-ref.rs:35:11
    |
 LL |     let &&&x = &(&1isize as &dyn T);
    |           ^^   -------------------- this expression has type `&&dyn T`
@@ -49,7 +49,7 @@ LL +     let &&x = &(&1isize as &dyn T);
    |
 
 error[E0308]: mismatched types
-  --> $DIR/destructure-trait-ref.rs:40:13
+  --> $DIR/destructure-trait-ref.rs:39:13
    |
 LL |     let box box x = Box::new(1isize) as Box<dyn T>;
    |             ^^^^^   ------------------------------ this expression has type `Box<dyn T>`

tests/ui/unboxed-closures/unboxed-closure-region.rs

@@ -1,5 +1,5 @@
-// Test that an unboxed closure that captures a free variable by
-// reference cannot escape the region of that variable.
+// Test that an unboxed closure that captures a free variable by reference
+// cannot escape the region of that variable.
 
 
 fn main() {

tests/ui/variance/variance-use-covariant-struct-1.rs

@@ -1,5 +1,4 @@
-// Test that a covariant struct does not permit the lifetime of a
-// reference to be enlarged.
+// Test that a covariant struct does not permit the lifetime of a reference to be enlarged.
 
 struct SomeStruct<T>(T);
 

tests/ui/variance/variance-use-covariant-struct-1.stderr

@@ -1,5 +1,5 @@
 error: lifetime may not live long enough
-  --> $DIR/variance-use-covariant-struct-1.rs:10:5
+  --> $DIR/variance-use-covariant-struct-1.rs:9:5
    |
 LL | fn foo<'min,'max>(v: SomeStruct<&'min ()>)
    |        ---- ---- lifetime `'max` defined here