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 (https://github.com/rust-lang/rust/issues/61687).

Other changes:
- You can now define a derive macro with a name matching one of the built-in derives (https://github.com/rust-lang/rust/issues/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 https://github.com/rust-lang/rust/issues/61687
Fixes https://github.com/rust-lang/rust/issues/61804
r? @eddyb

2 files changed, 6 insertions, 1 deletions

diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 11b7a984aaa..0ab14bee160 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -592,6 +592,9 @@ pub struct SyntaxExtension {
     pub helper_attrs: Vec<Symbol>,
     /// Edition of the crate in which this macro is defined.
     pub edition: Edition,
+    /// Built-in macros have a couple of special properties (meaning of `$crate`,
+    /// availability in `#[no_implicit_prelude]` modules), so we have to keep this flag.
+    pub is_builtin: bool,
 }
 
 impl SyntaxExtensionKind {
@@ -636,6 +639,7 @@ impl SyntaxExtension {
             deprecation: None,
             helper_attrs: Vec::new(),
             edition,
+            is_builtin: false,
             kind,
         }
     }
@@ -687,7 +691,7 @@ pub trait Resolver {
     fn resolve_dollar_crates(&mut self);
     fn visit_ast_fragment_with_placeholders(&mut self, expn_id: ExpnId, fragment: &AstFragment,
                                             derives: &[ExpnId]);
-    fn add_builtin(&mut self, ident: ast::Ident, ext: Lrc<SyntaxExtension>);
+    fn register_builtin_macro(&mut self, ident: ast::Ident, ext: SyntaxExtension);
 
     fn resolve_imports(&mut self);
 
diff --git a/src/libsyntax/ext/tt/macro_rules.rs b/src/libsyntax/ext/tt/macro_rules.rs
index 817d8547e87..2a2df76d30c 100644
--- a/src/libsyntax/ext/tt/macro_rules.rs
+++ b/src/libsyntax/ext/tt/macro_rules.rs
@@ -437,6 +437,7 @@ pub fn compile(
         deprecation: attr::find_deprecation(&sess, &def.attrs, def.span),
         helper_attrs: Vec::new(),
         edition,
+        is_builtin: attr::contains_name(&def.attrs, sym::rustc_builtin_macro),
     }
 }