Add #[cfg(panic = '...')]

compiler/rustc_feature/src/active.rs

@@ -613,6 +613,9 @@ declare_features! (
     /// Allows the use of destructuring assignments.
     (active, destructuring_assignment, "1.49.0", Some(71126), None),
 
+    /// Enables `#[cfg(panic = "...")]` config key.
+    (active, cfg_panic, "1.49.0", Some(77443), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------

compiler/rustc_feature/src/builtin_attrs.rs

@@ -33,6 +33,7 @@ const GATED_CFGS: &[GatedCfg] = &[
     ),
     (sym::sanitize, sym::cfg_sanitize, cfg_fn!(cfg_sanitize)),
     (sym::version, sym::cfg_version, cfg_fn!(cfg_version)),
+    (sym::panic, sym::cfg_panic, cfg_fn!(cfg_panic)),
 ];
 
 /// Find a gated cfg determined by the `pred`icate which is given the cfg's name.

compiler/rustc_session/src/config.rs

@@ -793,6 +793,9 @@ pub fn default_configuration(sess: &Session) -> CrateConfig {
         }
     }
 
+    let panic_strategy = sess.panic_strategy();
+    ret.insert((sym::panic, Some(panic_strategy.desc_symbol())));
+
     for s in sess.opts.debugging_opts.sanitizer {
         let symbol = Symbol::intern(&s.to_string());
         ret.insert((sym::sanitize, Some(symbol)));

compiler/rustc_span/src/symbol.rs

@@ -326,6 +326,7 @@ symbols! {
         cfg_attr,
         cfg_attr_multi,
         cfg_doctest,
+        cfg_panic,
         cfg_sanitize,
         cfg_target_feature,
         cfg_target_has_atomic,

compiler/rustc_target/src/spec/mod.rs

@@ -37,6 +37,7 @@
 use crate::spec::abi::{lookup as lookup_abi, Abi};
 use crate::spec::crt_objects::{CrtObjects, CrtObjectsFallback};
 use rustc_serialize::json::{Json, ToJson};
+use rustc_span::symbol::{sym, Symbol};
 use std::collections::BTreeMap;
 use std::ops::Deref;
 use std::path::{Path, PathBuf};
@@ -176,6 +177,13 @@ impl PanicStrategy {
             PanicStrategy::Abort => "abort",
         }
     }
+
+    pub fn desc_symbol(&self) -> Symbol {
+        match *self {
+            PanicStrategy::Unwind => sym::unwind,
+            PanicStrategy::Abort => sym::abort,
+        }
+    }
 }
 
 impl ToJson for PanicStrategy {

src/doc/unstable-book/src/language-features/cfg-panic.md

@@ -0,0 +1,38 @@
+# `cfg_panic`
+
+The tracking issue for this feature is: [#77443]
+
+[#77443]: https://github.com/rust-lang/rust/issues/77443
+
+------------------------
+
+The `cfg_panic` feature makes it possible to execute different code
+depending on the panic strategy.
+
+Possible values at the moment are `"unwind"` or `"abort"`, although
+it is possible that new panic strategies may be added to Rust in the
+future.
+
+## Examples
+
+```rust
+#![feature(cfg_panic)]
+
+#[cfg(panic = "unwind")]
+fn a() {
+    // ...
+}
+
+#[cfg(not(panic = "unwind"))]
+fn a() {
+    // ...
+}
+
+fn b() {
+    if cfg!(panic = "abort") {
+        // ...
+    } else {
+        // ...
+    }
+}
+```

src/test/ui/cfg/cfg-panic-abort.rs

@@ -0,0 +1,16 @@
+// build-pass
+// compile-flags: -C panic=abort
+// no-prefer-dynamic
+#![feature(cfg_panic)]
+
+#[cfg(panic = "unwind")]
+pub fn bad() -> i32 { }
+
+#[cfg(not(panic = "abort"))]
+pub fn bad() -> i32 { }
+
+#[cfg(panic = "some_imaginary_future_panic_handler")]
+pub fn bad() -> i32 { }
+
+#[cfg(panic = "abort")]
+pub fn main() { }

src/test/ui/cfg/cfg-panic.rs

@@ -0,0 +1,18 @@
+// build-pass
+// compile-flags: -C panic=unwind
+// ignore-emscripten no panic_unwind implementation
+// ignore-wasm32     no panic_unwind implementation
+// ignore-wasm64     no panic_unwind implementation
+#![feature(cfg_panic)]
+
+#[cfg(panic = "abort")]
+pub fn bad() -> i32 { }
+
+#[cfg(not(panic = "unwind"))]
+pub fn bad() -> i32 { }
+
+#[cfg(panic = "some_imaginary_future_panic_handler")]
+pub fn bad() -> i32 { }
+
+#[cfg(panic = "unwind")]
+pub fn main() { }

src/test/ui/consts/control-flow/assert.rs

@@ -1,14 +1,14 @@
 // Test that `assert` works when `const_panic` is enabled.
 
-// revisions: stock panic
+// revisions: stock const_panic
 
-#![cfg_attr(panic, feature(const_panic))]
+#![cfg_attr(const_panic, feature(const_panic))]
 
 const _: () = assert!(true);
 //[stock]~^ ERROR panicking in constants is unstable
 
 const _: () = assert!(false);
 //[stock]~^ ERROR panicking in constants is unstable
-//[panic]~^^ ERROR any use of this value will cause an error
+//[const_panic]~^^ ERROR any use of this value will cause an error
 
 fn main() {}

src/test/ui/feature-gates/feature-gate-cfg-panic.rs

@@ -0,0 +1,11 @@
+#[cfg(panic = "unwind")]
+//~^ ERROR `cfg(panic)` is experimental and subject to change
+fn foo() -> bool { true }
+#[cfg(not(panic = "unwind"))]
+//~^ ERROR `cfg(panic)` is experimental and subject to change
+fn foo() -> bool { false }
+
+
+fn main() {
+    assert!(foo());
+}

src/test/ui/feature-gates/feature-gate-cfg-panic.stderr

@@ -0,0 +1,21 @@
+error[E0658]: `cfg(panic)` is experimental and subject to change
+  --> $DIR/feature-gate-cfg-panic.rs:1:7
+   |
+LL | #[cfg(panic = "unwind")]
+   |       ^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #77443 <https://github.com/rust-lang/rust/issues/77443> for more information
+   = help: add `#![feature(cfg_panic)]` to the crate attributes to enable
+
+error[E0658]: `cfg(panic)` is experimental and subject to change
+  --> $DIR/feature-gate-cfg-panic.rs:4:11
+   |
+LL | #[cfg(not(panic = "unwind"))]
+   |           ^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #77443 <https://github.com/rust-lang/rust/issues/77443> for more information
+   = help: add `#![feature(cfg_panic)]` to the crate attributes to enable
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/fmt/format-args-capture.rs

@@ -1,13 +1,16 @@
 // run-pass
-// ignore-wasm32
-// ignore-wasm64
 #![feature(format_args_capture)]
+#![feature(cfg_panic)]
 
 fn main() {
     named_argument_takes_precedence_to_captured();
-    panic_with_single_argument_does_not_get_formatted();
-    panic_with_multiple_arguments_is_formatted();
     formatting_parameters_can_be_captured();
+
+    #[cfg(panic = "unwind")]
+    {
+        panic_with_single_argument_does_not_get_formatted();
+        panic_with_multiple_arguments_is_formatted();
+    }
 }
 
 fn named_argument_takes_precedence_to_captured() {
@@ -22,6 +25,7 @@ fn named_argument_takes_precedence_to_captured() {
     assert_eq!(&s, "positional-named-captured");
 }
 
+#[cfg(panic = "unwind")]
 fn panic_with_single_argument_does_not_get_formatted() {
     // panic! with a single argument does not perform string formatting.
     // RFC #2795 suggests that this may need to change so that captured arguments are formatted.
@@ -34,6 +38,7 @@ fn panic_with_single_argument_does_not_get_formatted() {
     assert_eq!(msg.downcast_ref::<&str>(), Some(&"{foo}"))
 }
 
+#[cfg(panic = "unwind")]
 fn panic_with_multiple_arguments_is_formatted() {
     let foo = "captured";
 

src/test/ui/issues/issue-68696-catch-during-unwind.rs

@@ -4,8 +4,7 @@
 // entering the catch_unwind.
 //
 // run-pass
-// ignore-wasm       no panic support
-// ignore-emscripten no panic support
+#![feature(cfg_panic)]
 
 use std::panic::catch_unwind;
 
@@ -19,6 +18,7 @@ impl Drop for Guard {
 }
 
 fn main() {
+    #[cfg(panic = "unwind")]
     let _ = catch_unwind(|| {
         let _guard = Guard::default();
         panic!();

src/test/ui/test-attrs/test-allow-fail-attr.rs

@@ -1,11 +1,12 @@
 // run-pass
-// ignore-wasm32-bare compiled with panic=abort by default
 // compile-flags: --test
 #![feature(allow_fail)]
+#![feature(cfg_panic)]
 
 #[test]
 #[allow_fail]
 fn test1() {
+    #[cfg(not(panic = "abort"))]
     panic!();
 }