Auto merge of #62086 - petrochenkov:builtout, r=eddyb

Define built-in macros through libcore

This PR defines built-in macros through libcore using a scheme similar to lang items (attribute `#[rustc_builtin_macro]`).
All the macro properties (stability, visibility, etc.) are taken from the source code in libcore, with exception of the expander function transforming input tokens/AST into output tokens/AST, which is still provided by the compiler.

The macros are made available to user code through the standard library prelude (`{core,std}::prelude::v1`), so they are still always in scope.
As a result **built-in macros now have stable absolute addresses in the library**, like `core::prelude::v1::line!()`, this is an insta-stable change.

Right now `prelude::v1` is the only publicly available absolute address for these macros, but eventually they can be moved into more appropriate locations with library team approval (e.g. `Clone` derive -> `core::clone::Clone`).

Now when built-in macros have canonical definitions they can be imported or reexported without issues (#61687).

Other changes:
- You can now define a derive macro with a name matching one of the built-in derives (#52269). This was an artificial restriction that could be worked around with import renaming anyway.

Known regressions:
- Empty library crate with a crate-level `#![test]` attribute no longer compiles without `--test`. Previously it didn't compile *with* `--test` or with the bin crate type.

Fixes #61687
Fixes #61804
r? @eddyb

Author: bors

src/libcore/macros.rs

@@ -657,13 +657,13 @@ macro_rules! uninit_array {
     );
 }
 
-/// Built-in macros to the compiler itself.
+/// Definitions of built-in macros.
 ///
-/// These macros do not have any corresponding definition with a `macro_rules!`
-/// macro, but are documented here. Their implementations can be found hardcoded
-/// into libsyntax itself.
-#[cfg(rustdoc)]
-mod builtin {
+/// Most of the macro properties (stability, visibility, etc.) are taken from the source code here,
+/// with exception of expansion functions transforming macro inputs into outputs,
+/// those functions are provided by the compiler.
+#[cfg(not(bootstrap))]
+pub(crate) mod builtin {
 
     /// Causes compilation to fail with the given error message when encountered.
     ///
@@ -950,7 +950,7 @@ mod builtin {
 
     /// Same as `column`, but less likely to be shadowed.
     #[unstable(feature = "__rust_unstable_column", issue = "0",
-               reason = "internal implementation detail of the `column` macro")]
+               reason = "internal implementation detail of the `panic` macro")]
     #[rustc_builtin_macro]
     #[rustc_macro_transparency = "semitransparent"]
     pub macro __rust_unstable_column() { /* compiler built-in */ }

src/libcore/prelude/v1.rs

@@ -44,3 +44,50 @@ pub use crate::option::Option::{self, Some, None};
 #[stable(feature = "core_prelude", since = "1.4.0")]
 #[doc(no_inline)]
 pub use crate::result::Result::{self, Ok, Err};
+
+// Re-exported built-in macros
+#[cfg(not(bootstrap))]
+#[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
+#[allow(deprecated)]
+#[doc(no_inline)]
+pub use crate::macros::builtin::{
+    Clone,
+    Copy,
+    Debug,
+    Decodable,
+    Default,
+    Encodable,
+    Eq,
+    Hash,
+    Ord,
+    PartialEq,
+    PartialOrd,
+    RustcDecodable,
+    RustcEncodable,
+    __rust_unstable_column,
+    asm,
+    assert,
+    bench,
+    cfg,
+    column,
+    compile_error,
+    concat,
+    concat_idents,
+    env,
+    file,
+    format_args,
+    format_args_nl,
+    global_allocator,
+    global_asm,
+    include,
+    include_bytes,
+    include_str,
+    line,
+    log_syntax,
+    module_path,
+    option_env,
+    stringify,
+    test,
+    test_case,
+    trace_macros,
+};