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

19 files changed, 76 insertions, 89 deletions

diff --git a/src/test/ui/feature-gate/issue-43106-gating-of-bench.rs b/src/test/ui/feature-gate/issue-43106-gating-of-bench.rs
index 2d8868995f4..31eee88d1fa 100644
--- a/src/test/ui/feature-gate/issue-43106-gating-of-bench.rs
+++ b/src/test/ui/feature-gate/issue-43106-gating-of-bench.rs
@@ -1,17 +1,10 @@
-// error-pattern: `main` function not found
-
-// At time of authorship, a crate-level #![bench] with no `--test`
-// will cause compilation to error unconditionally with "main function
-// not found" (despite having one), similar to #[bench].
-//
-// (The non-crate level cases are in
-// issue-43106-gating-of-builtin-attrs.rs.)
-
+// The non-crate level cases are in issue-43106-gating-of-builtin-attrs.rs.
 // See issue-12997-1.rs and issue-12997-2.rs to see how `#[bench]` is
 // handled in "weird places" when `--test` is passed.
 
 #![feature(custom_inner_attributes)]
 
 #![bench                   = "4100"]
+//~^ ERROR cannot determine resolution for the attribute macro `bench`
 
-fn main() { }
+fn main() {}
diff --git a/src/test/ui/feature-gate/issue-43106-gating-of-bench.stderr b/src/test/ui/feature-gate/issue-43106-gating-of-bench.stderr
index 37b5e792dc2..d0305c5160f 100644
--- a/src/test/ui/feature-gate/issue-43106-gating-of-bench.stderr
+++ b/src/test/ui/feature-gate/issue-43106-gating-of-bench.stderr
@@ -1,17 +1,10 @@
-warning: attribute must be of the form `#[bench]`
-  --> $DIR/issue-43106-gating-of-bench.rs:15:1
+error: cannot determine resolution for the attribute macro `bench`
+  --> $DIR/issue-43106-gating-of-bench.rs:7:4
    |
 LL | #![bench                   = "4100"]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |    ^^^^^
    |
-   = note: `#[warn(ill_formed_attribute_input)]` on by default
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #57571 <https://github.com/rust-lang/rust/issues/57571>
-
-error[E0601]: `main` function not found in crate `issue_43106_gating_of_bench`
-   |
-   = note: consider adding a `main` function to `$DIR/issue-43106-gating-of-bench.rs`
+   = note: import resolution is stuck, try simplifying macro imports
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0601`.
diff --git a/src/test/ui/feature-gate/issue-43106-gating-of-test.rs b/src/test/ui/feature-gate/issue-43106-gating-of-test.rs
index c0c49d35300..d343746955f 100644
--- a/src/test/ui/feature-gate/issue-43106-gating-of-test.rs
+++ b/src/test/ui/feature-gate/issue-43106-gating-of-test.rs
@@ -1,12 +1,6 @@
-// error-pattern: `main` function not found
-
-// At time of authorship, crate-level #[test] attribute with no
-// `--test` signals unconditional error complaining of missing main
-// function (despite having one), similar to #[bench].
-//
-// (The non-crate level cases are in
-// issue-43106-gating-of-builtin-attrs.rs.)
+// The non-crate level cases are in issue-43106-gating-of-builtin-attrs.rs.
 
 #![test                    = "4200"]
+//~^ ERROR cannot determine resolution for the attribute macro `test`
 
-fn main() { }
+fn main() {}
diff --git a/src/test/ui/feature-gate/issue-43106-gating-of-test.stderr b/src/test/ui/feature-gate/issue-43106-gating-of-test.stderr
index dbffabf3e02..a7d3a1e1684 100644
--- a/src/test/ui/feature-gate/issue-43106-gating-of-test.stderr
+++ b/src/test/ui/feature-gate/issue-43106-gating-of-test.stderr
@@ -1,17 +1,10 @@
-warning: attribute must be of the form `#[test]`
-  --> $DIR/issue-43106-gating-of-test.rs:10:1
+error: cannot determine resolution for the attribute macro `test`
+  --> $DIR/issue-43106-gating-of-test.rs:3:4
    |
 LL | #![test                    = "4200"]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |    ^^^^
    |
-   = note: `#[warn(ill_formed_attribute_input)]` on by default
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #57571 <https://github.com/rust-lang/rust/issues/57571>
-
-error[E0601]: `main` function not found in crate `issue_43106_gating_of_test`
-   |
-   = note: consider adding a `main` function to `$DIR/issue-43106-gating-of-test.rs`
+   = note: import resolution is stuck, try simplifying macro imports
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0601`.
diff --git a/src/test/ui/feature-gates/feature-gate-cfg-target-has-atomic.rs b/src/test/ui/feature-gates/feature-gate-cfg-target-has-atomic.rs
index 827ac3af8f1..506b21dc7d5 100644
--- a/src/test/ui/feature-gates/feature-gate-cfg-target-has-atomic.rs
+++ b/src/test/ui/feature-gates/feature-gate-cfg-target-has-atomic.rs
@@ -1,4 +1,4 @@
-#![feature(intrinsics, lang_items, no_core)]
+#![feature(intrinsics, lang_items, no_core, rustc_attrs)]
 
 #![crate_type="rlib"]
 #![no_core]
@@ -88,3 +88,7 @@ fn main() {
     cfg!(target_has_atomic = "ptr");
     //~^ ERROR `cfg(target_has_atomic)` is experimental and subject to change
 }
+
+#[macro_export]
+#[rustc_builtin_macro]
+macro_rules! cfg { () => () }
diff --git a/src/test/ui/imports/glob-shadowing.stderr b/src/test/ui/imports/glob-shadowing.stderr
index 7962fcb9aec..4ef446f93c8 100644
--- a/src/test/ui/imports/glob-shadowing.stderr
+++ b/src/test/ui/imports/glob-shadowing.stderr
@@ -4,7 +4,7 @@ error[E0659]: `env` is ambiguous (glob import vs any other name from outer scope
 LL |         let x = env!("PATH");
    |                 ^^^ ambiguous name
    |
-   = note: `env` could refer to a built-in macro
+   = note: `env` could refer to a macro from prelude
 note: `env` could also refer to the macro imported here
   --> $DIR/glob-shadowing.rs:9:9
    |
@@ -19,7 +19,7 @@ error[E0659]: `env` is ambiguous (glob import vs any other name from outer scope
 LL |             let x = env!("PATH");
    |                     ^^^ ambiguous name
    |
-   = note: `env` could refer to a built-in macro
+   = note: `env` could refer to a macro from prelude
 note: `env` could also refer to the macro imported here
   --> $DIR/glob-shadowing.rs:17:13
    |
diff --git a/src/test/ui/imports/local-modularized-tricky-fail-1.stderr b/src/test/ui/imports/local-modularized-tricky-fail-1.stderr
index 13d3227d8b3..5afdd8889ae 100644
--- a/src/test/ui/imports/local-modularized-tricky-fail-1.stderr
+++ b/src/test/ui/imports/local-modularized-tricky-fail-1.stderr
@@ -27,7 +27,7 @@ error[E0659]: `include` is ambiguous (macro-expanded name vs less macro-expanded
 LL | include!();
    | ^^^^^^^ ambiguous name
    |
-   = note: `include` could refer to a built-in macro
+   = note: `include` could refer to a macro from prelude
 note: `include` could also refer to the macro defined here
   --> $DIR/local-modularized-tricky-fail-1.rs:17:5
    |
diff --git a/src/test/ui/issues/issue-28134.rs b/src/test/ui/issues/issue-28134.rs
index 2bd4f93791d..fa692db4bf6 100644
--- a/src/test/ui/issues/issue-28134.rs
+++ b/src/test/ui/issues/issue-28134.rs
@@ -1,3 +1,3 @@
 // compile-flags: --test
 
-#![test] //~ ERROR only functions may be used as tests
+#![test] //~ ERROR cannot determine resolution for the attribute macro `test`
diff --git a/src/test/ui/issues/issue-28134.stderr b/src/test/ui/issues/issue-28134.stderr
index b9189480048..5f8d27dd043 100644
--- a/src/test/ui/issues/issue-28134.stderr
+++ b/src/test/ui/issues/issue-28134.stderr
@@ -1,8 +1,10 @@
-error: only functions may be used as tests
-  --> $DIR/issue-28134.rs:3:1
+error: cannot determine resolution for the attribute macro `test`
+  --> $DIR/issue-28134.rs:3:4
    |
 LL | #![test]
-   | ^^^^^^^^
+   |    ^^^^
+   |
+   = note: import resolution is stuck, try simplifying macro imports
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/macros/unknown-builtin.rs b/src/test/ui/macros/unknown-builtin.rs
new file mode 100644
index 00000000000..a96b99ae4ff
--- /dev/null
+++ b/src/test/ui/macros/unknown-builtin.rs
@@ -0,0 +1,14 @@
+// error-pattern: cannot find a built-in macro with name `line`
+
+#![feature(rustc_attrs)]
+
+#[rustc_builtin_macro]
+macro_rules! unknown { () => () } //~ ERROR cannot find a built-in macro with name `unknown`
+
+#[rustc_builtin_macro]
+macro_rules! line { () => () }
+
+fn main() {
+    line!();
+    std::prelude::v1::line!();
+}
diff --git a/src/test/ui/macros/unknown-builtin.stderr b/src/test/ui/macros/unknown-builtin.stderr
new file mode 100644
index 00000000000..33b7b055b4e
--- /dev/null
+++ b/src/test/ui/macros/unknown-builtin.stderr
@@ -0,0 +1,14 @@
+error: cannot find a built-in macro with name `unknown`
+  --> $DIR/unknown-builtin.rs:6:1
+   |
+LL | macro_rules! unknown { () => () }
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: cannot find a built-in macro with name `line`
+  --> <::core::macros::builtin::line macros>:1:1
+   |
+LL | () => { }
+   | ^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
diff --git a/src/test/ui/proc-macro/attribute.rs b/src/test/ui/proc-macro/attribute.rs
index 04c88dcef50..5531b323621 100644
--- a/src/test/ui/proc-macro/attribute.rs
+++ b/src/test/ui/proc-macro/attribute.rs
@@ -40,8 +40,7 @@ pub fn foo8(input: TokenStream) -> TokenStream { input }
 //~^ ERROR: `self` cannot be a name of derive macro
 pub fn foo9(input: TokenStream) -> TokenStream { input }
 
-#[proc_macro_derive(PartialEq)]
-//~^ ERROR: cannot override a built-in derive macro
+#[proc_macro_derive(PartialEq)] // OK
 pub fn foo10(input: TokenStream) -> TokenStream { input }
 
 #[proc_macro_derive(d11, a)]
diff --git a/src/test/ui/proc-macro/attribute.stderr b/src/test/ui/proc-macro/attribute.stderr
index e632875cb16..1503f62cb6c 100644
--- a/src/test/ui/proc-macro/attribute.stderr
+++ b/src/test/ui/proc-macro/attribute.stderr
@@ -40,56 +40,50 @@ error: `self` cannot be a name of derive macro
 LL | #[proc_macro_derive(self)]
    |                     ^^^^
 
-error: cannot override a built-in derive macro
-  --> $DIR/attribute.rs:43:21
-   |
-LL | #[proc_macro_derive(PartialEq)]
-   |                     ^^^^^^^^^
-
 error: second argument must be `attributes`
-  --> $DIR/attribute.rs:47:26
+  --> $DIR/attribute.rs:46:26
    |
 LL | #[proc_macro_derive(d11, a)]
    |                          ^
 
 error: attribute must be of form: `attributes(foo, bar)`
-  --> $DIR/attribute.rs:47:26
+  --> $DIR/attribute.rs:46:26
    |
 LL | #[proc_macro_derive(d11, a)]
    |                          ^
 
 error: attribute must be of form: `attributes(foo, bar)`
-  --> $DIR/attribute.rs:52:26
+  --> $DIR/attribute.rs:51:26
    |
 LL | #[proc_macro_derive(d12, attributes)]
    |                          ^^^^^^^^^^
 
 error: not a meta item
-  --> $DIR/attribute.rs:56:37
+  --> $DIR/attribute.rs:55:37
    |
 LL | #[proc_macro_derive(d13, attributes("a"))]
    |                                     ^^^
 
 error: must only be one word
-  --> $DIR/attribute.rs:60:37
+  --> $DIR/attribute.rs:59:37
    |
 LL | #[proc_macro_derive(d14, attributes(a = ""))]
    |                                     ^^^^^^
 
 error: must only be one word
-  --> $DIR/attribute.rs:64:37
+  --> $DIR/attribute.rs:63:37
    |
 LL | #[proc_macro_derive(d15, attributes(m::a))]
    |                                     ^^^^
 
 error: must only be one word
-  --> $DIR/attribute.rs:68:37
+  --> $DIR/attribute.rs:67:37
    |
 LL | #[proc_macro_derive(d16, attributes(a(b)))]
    |                                     ^^^^
 
 error: `self` cannot be a name of derive helper attribute
-  --> $DIR/attribute.rs:72:37
+  --> $DIR/attribute.rs:71:37
    |
 LL | #[proc_macro_derive(d17, attributes(self))]
    |                                     ^^^^
@@ -106,5 +100,5 @@ error: malformed `proc_macro_derive` attribute input
 LL | #[proc_macro_derive = ""]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^ help: must be of the form: `#[proc_macro_derive(TraitName, /*opt*/ attributes(name1, name2, ...))]`
 
-error: aborting due to 18 previous errors
+error: aborting due to 17 previous errors
 
diff --git a/src/test/ui/rfc-2126-extern-absolute-paths/not-whitelisted.rs b/src/test/ui/rfc-2126-extern-absolute-paths/not-whitelisted.rs
index dd21de75aaf..acb4bbebe7f 100644
--- a/src/test/ui/rfc-2126-extern-absolute-paths/not-whitelisted.rs
+++ b/src/test/ui/rfc-2126-extern-absolute-paths/not-whitelisted.rs
@@ -3,7 +3,7 @@
 // Tests that arbitrary crates (other than `core`, `std` and `meta`)
 // aren't allowed without `--extern`, even if they're in the sysroot.
 use alloc; //~ ERROR unresolved import `alloc`
-use test; //~ ERROR cannot import a built-in macro
+use test; // OK, imports the built-in attribute macro `#[test]`, but not the `test` crate.
 use proc_macro; // OK, imports the built-in `proc_macro` attribute, but not the `proc_macro` crate.
 
 fn main() {}
diff --git a/src/test/ui/rfc-2126-extern-absolute-paths/not-whitelisted.stderr b/src/test/ui/rfc-2126-extern-absolute-paths/not-whitelisted.stderr
index 4e3fff98e6f..f324378d4ca 100644
--- a/src/test/ui/rfc-2126-extern-absolute-paths/not-whitelisted.stderr
+++ b/src/test/ui/rfc-2126-extern-absolute-paths/not-whitelisted.stderr
@@ -1,15 +1,9 @@
-error: cannot import a built-in macro
-  --> $DIR/not-whitelisted.rs:6:5
-   |
-LL | use test;
-   |     ^^^^
-
 error[E0432]: unresolved import `alloc`
   --> $DIR/not-whitelisted.rs:5:5
    |
 LL | use alloc;
    |     ^^^^^ no `alloc` external crate
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0432`.
diff --git a/src/test/ui/rust-2018/uniform-paths/prelude-fail.rs b/src/test/ui/rust-2018/uniform-paths/prelude-fail.rs
index d717884c901..48c33d720dc 100644
--- a/src/test/ui/rust-2018/uniform-paths/prelude-fail.rs
+++ b/src/test/ui/rust-2018/uniform-paths/prelude-fail.rs
@@ -1,11 +1,6 @@
 // edition:2018
 
-// Built-in macro
-use env as env_imported; //~ ERROR cannot import a built-in macro
-
 // Tool attribute
 use rustfmt::skip as imported_rustfmt_skip; //~ ERROR unresolved import `rustfmt`
 
-fn main() {
-    env_imported!("PATH");
-}
+fn main() {}
diff --git a/src/test/ui/rust-2018/uniform-paths/prelude-fail.stderr b/src/test/ui/rust-2018/uniform-paths/prelude-fail.stderr
index 42daf7c6fb1..97d4c736751 100644
--- a/src/test/ui/rust-2018/uniform-paths/prelude-fail.stderr
+++ b/src/test/ui/rust-2018/uniform-paths/prelude-fail.stderr
@@ -1,15 +1,9 @@
-error: cannot import a built-in macro
-  --> $DIR/prelude-fail.rs:4:5
-   |
-LL | use env as env_imported;
-   |     ^^^^^^^^^^^^^^^^^^^
-
 error[E0432]: unresolved import `rustfmt`
-  --> $DIR/prelude-fail.rs:7:5
+  --> $DIR/prelude-fail.rs:4:5
    |
 LL | use rustfmt::skip as imported_rustfmt_skip;
    |     ^^^^^^^ `rustfmt` is a tool module, not a module
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0432`.
diff --git a/src/test/ui/rust-2018/uniform-paths/prelude.rs b/src/test/ui/rust-2018/uniform-paths/prelude.rs
index dca9587c5d3..65763614ce0 100644
--- a/src/test/ui/rust-2018/uniform-paths/prelude.rs
+++ b/src/test/ui/rust-2018/uniform-paths/prelude.rs
@@ -10,9 +10,13 @@ use Vec as ImportedVec;
 // Built-in type
 use u8 as imported_u8;
 
+// Built-in macro
+use env as env_imported;
+
 type A = imported_u8;
 
 fn main() {
     imported_vec![0];
     ImportedVec::<u8>::new();
+    env_imported!("PATH");
 }
diff --git a/src/test/ui/rust-unstable-column-gated.stderr b/src/test/ui/rust-unstable-column-gated.stderr
index c581a16dbb0..7db1b01fb0e 100644
--- a/src/test/ui/rust-unstable-column-gated.stderr
+++ b/src/test/ui/rust-unstable-column-gated.stderr
@@ -1,4 +1,4 @@
-error[E0658]: use of unstable library feature '__rust_unstable_column': internal implementation detail of the `column` macro
+error[E0658]: use of unstable library feature '__rust_unstable_column': internal implementation detail of the `panic` macro
   --> $DIR/rust-unstable-column-gated.rs:2:20
    |
 LL |     println!("{}", __rust_unstable_column!());