Auto merge of #93179 - Urgau:unreachable-2021, r=m-ou-se,oli-obk

Fix invalid special casing of the unreachable! macro

This pull-request fix an invalid special casing of the `unreachable!` macro in the same way the `panic!` macro was solved, by adding two new internal only macros `unreachable_2015` and `unreachable_2021` edition dependent and turn `unreachable!` into a built-in macro that do dispatching. This logic is stolen from the `panic!` macro.

~~This pull-request also adds an internal feature `format_args_capture_non_literal` that allows capturing arguments from formatted string that expanded from macros. The original RFC #2795 mentioned this as a future possibility. This feature is [required](#92137 (comment)) because of concatenation that needs to be done inside the macro:~~
```rust
$crate::concat!("internal error: entered unreachable code: ", $fmt)
```

**In summary** the new behavior for the `unreachable!` macro with this pr is:

Edition 2021:
```rust
let x = 5;
unreachable!("x is {x}");
```
```
internal error: entered unreachable code: x is 5
```

Edition <= 2018:
```rust
let x = 5;
unreachable!("x is {x}");
```
```
internal error: entered unreachable code: x is {x}
```

Also note that the change in this PR are **insta-stable** and **breaking changes** but this a considered as being a [bug](#92137 (comment)).
If someone could start a perf run and then a crater run this would be appreciated.

Fixes #92137

Author: bors

compiler/rustc_builtin_macros/src/assert.rs

@@ -1,4 +1,4 @@
-use crate::panic::use_panic_2021;
+use crate::edition_panic::use_panic_2021;
 use rustc_ast::ptr::P;
 use rustc_ast::token;
 use rustc_ast::tokenstream::{DelimSpan, TokenStream};

compiler/rustc_builtin_macros/src/panic.rs renamed to compiler/rustc_builtin_macros/src/edition_panic.rs

@@ -20,8 +20,29 @@ pub fn expand_panic<'cx>(
     sp: Span,
     tts: TokenStream,
 ) -> Box<dyn MacResult + 'cx> {
-    let panic = if use_panic_2021(sp) { sym::panic_2021 } else { sym::panic_2015 };
+    let mac = if use_panic_2021(sp) { sym::panic_2021 } else { sym::panic_2015 };
+    expand(mac, cx, sp, tts)
+}
 
+// This expands to either
+// - `$crate::panic::unreachable_2015!(...)` or
+// - `$crate::panic::unreachable_2021!(...)`
+// depending on the edition.
+pub fn expand_unreachable<'cx>(
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn MacResult + 'cx> {
+    let mac = if use_panic_2021(sp) { sym::unreachable_2021 } else { sym::unreachable_2015 };
+    expand(mac, cx, sp, tts)
+}
+
+fn expand<'cx>(
+    mac: rustc_span::Symbol,
+    cx: &'cx mut ExtCtxt<'_>,
+    sp: Span,
+    tts: TokenStream,
+) -> Box<dyn MacResult + 'cx> {
     let sp = cx.with_call_site_ctxt(sp);
 
     MacEager::expr(
@@ -31,7 +52,7 @@ pub fn expand_panic<'cx>(
                 path: Path {
                     span: sp,
                     segments: cx
-                        .std_path(&[sym::panic, panic])
+                        .std_path(&[sym::panic, mac])
                         .into_iter()
                         .map(|ident| PathSegment::from_ident(ident))
                         .collect(),

compiler/rustc_builtin_macros/src/lib.rs

@@ -32,12 +32,12 @@ mod concat_bytes;
 mod concat_idents;
 mod derive;
 mod deriving;
+mod edition_panic;
 mod env;
 mod format;
 mod format_foreign;
 mod global_allocator;
 mod log_syntax;
-mod panic;
 mod source_util;
 mod test;
 mod trace_macros;
@@ -83,8 +83,9 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
         log_syntax: log_syntax::expand_log_syntax,
         module_path: source_util::expand_mod,
         option_env: env::expand_option_env,
-        core_panic: panic::expand_panic,
-        std_panic: panic::expand_panic,
+        core_panic: edition_panic::expand_panic,
+        std_panic: edition_panic::expand_panic,
+        unreachable: edition_panic::expand_unreachable,
         stringify: source_util::expand_stringify,
         trace_macros: trace_macros::expand_trace_macros,
     }

compiler/rustc_hir/src/lang_items.rs

@@ -277,7 +277,6 @@ language_item_table! {
     Panic,                   sym::panic,               panic_fn,                   Target::Fn,             GenericRequirement::Exact(0);
     PanicFmt,                sym::panic_fmt,           panic_fmt,                  Target::Fn,             GenericRequirement::None;
     PanicDisplay,            sym::panic_display,       panic_display,              Target::Fn,             GenericRequirement::None;
-    PanicStr,                sym::panic_str,           panic_str,                  Target::Fn,             GenericRequirement::None;
     ConstPanicFmt,           sym::const_panic_fmt,     const_panic_fmt,            Target::Fn,             GenericRequirement::None;
     PanicBoundsCheck,        sym::panic_bounds_check,  panic_bounds_check_fn,      Target::Fn,             GenericRequirement::Exact(0);
     PanicInfo,               sym::panic_info,          panic_info,                 Target::Struct,         GenericRequirement::None;

compiler/rustc_lint/src/non_fmt_panic.rs

@@ -49,9 +49,11 @@ impl<'tcx> LateLintPass<'tcx> for NonPanicFmt {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
         if let hir::ExprKind::Call(f, [arg]) = &expr.kind {
             if let &ty::FnDef(def_id, _) = cx.typeck_results().expr_ty(f).kind() {
+                let f_diagnostic_name = cx.tcx.get_diagnostic_name(def_id);
+
                 if Some(def_id) == cx.tcx.lang_items().begin_panic_fn()
                     || Some(def_id) == cx.tcx.lang_items().panic_fn()
-                    || Some(def_id) == cx.tcx.lang_items().panic_str()
+                    || f_diagnostic_name == Some(sym::panic_str)
                 {
                     if let Some(id) = f.span.ctxt().outer_expn_data().macro_def_id {
                         if matches!(
@@ -61,6 +63,22 @@ impl<'tcx> LateLintPass<'tcx> for NonPanicFmt {
                             check_panic(cx, f, arg);
                         }
                     }
+                } else if f_diagnostic_name == Some(sym::unreachable_display) {
+                    if let Some(id) = f.span.ctxt().outer_expn_data().macro_def_id {
+                        if cx.tcx.is_diagnostic_item(sym::unreachable_2015_macro, id) {
+                            check_panic(
+                                cx,
+                                f,
+                                // This is safe because we checked above that the callee is indeed
+                                // unreachable_display
+                                match &arg.kind {
+                                    // Get the borrowed arg not the borrow
+                                    hir::ExprKind::AddrOf(ast::BorrowKind::Ref, _, arg) => arg,
+                                    _ => bug!("call to unreachable_display without borrow"),
+                                },
+                            );
+                        }
+                    }
                 }
             }
         }
@@ -85,8 +103,8 @@ fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tc
         return;
     }
 
-    // Find the span of the argument to `panic!()`, before expansion in the
-    // case of `panic!(some_macro!())`.
+    // Find the span of the argument to `panic!()` or `unreachable!`, before expansion in the
+    // case of `panic!(some_macro!())` or `unreachable!(some_macro!())`.
     // We don't use source_callsite(), because this `panic!(..)` might itself
     // be expanded from another macro, in which case we want to stop at that
     // expansion.
@@ -319,6 +337,7 @@ fn panic_call<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>) -> (Span,
                 | sym::std_panic_macro
                 | sym::assert_macro
                 | sym::debug_assert_macro
+                | sym::unreachable_macro
         ) {
             break;
         }

compiler/rustc_span/src/symbol.rs

@@ -1437,7 +1437,12 @@ symbols! {
         unmarked_api,
         unpin,
         unreachable,
+        unreachable_2015,
+        unreachable_2015_macro,
+        unreachable_2021,
+        unreachable_2021_macro,
         unreachable_code,
+        unreachable_display,
         unreachable_macro,
         unrestricted_attribute_tokens,
         unsafe_block_in_unsafe_fn,

library/core/src/macros/mod.rs

@@ -594,6 +594,22 @@ macro_rules! writeln {
 ///     unreachable!("The loop should always return");
 /// }
 /// ```
+#[cfg(not(bootstrap))]
+#[macro_export]
+#[rustc_builtin_macro(unreachable)]
+#[allow_internal_unstable(edition_panic)]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[cfg_attr(not(test), rustc_diagnostic_item = "unreachable_macro")]
+macro_rules! unreachable {
+    // Expands to either `$crate::panic::unreachable_2015` or `$crate::panic::unreachable_2021`
+    // depending on the edition of the caller.
+    ($($arg:tt)*) => {
+        /* compiler built-in */
+    };
+}
+
+/// unreachable!() macro
+#[cfg(bootstrap)]
 #[macro_export]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "unreachable_macro")]

library/core/src/panic.rs

@@ -58,6 +58,39 @@ pub macro panic_2021 {
     ),
 }
 
+#[doc(hidden)]
+#[unstable(feature = "edition_panic", issue = "none", reason = "use unreachable!() instead")]
+#[allow_internal_unstable(core_panic)]
+#[rustc_diagnostic_item = "unreachable_2015_macro"]
+#[rustc_macro_transparency = "semitransparent"]
+pub macro unreachable_2015 {
+    () => (
+        $crate::panicking::panic("internal error: entered unreachable code")
+    ),
+    // Use of `unreachable_display` for non_fmt_panic lint.
+    // NOTE: the message ("internal error ...") is embeded directly in unreachable_display
+    ($msg:expr $(,)?) => (
+        $crate::panicking::unreachable_display(&$msg)
+    ),
+    ($fmt:expr, $($arg:tt)*) => (
+        $crate::panic!($crate::concat!("internal error: entered unreachable code: ", $fmt), $($arg)*)
+    ),
+}
+
+#[doc(hidden)]
+#[unstable(feature = "edition_panic", issue = "none", reason = "use unreachable!() instead")]
+#[allow_internal_unstable(core_panic)]
+#[rustc_diagnostic_item = "unreachable_2021_macro"]
+#[rustc_macro_transparency = "semitransparent"]
+pub macro unreachable_2021 {
+    () => (
+        $crate::panicking::panic("internal error: entered unreachable code")
+    ),
+    ($($t:tt)+) => (
+        $crate::panic!("internal error: entered unreachable code: {}", $crate::format_args!($($t)+))
+    ),
+}
+
 /// An internal trait used by libstd to pass data from libstd to `panic_unwind`
 /// and other panic runtimes. Not intended to be stabilized any time soon, do
 /// not use.

library/core/src/panicking.rs

@@ -50,12 +50,20 @@ pub const fn panic(expr: &'static str) -> ! {
 
 #[inline]
 #[track_caller]
-#[lang = "panic_str"] // needed for `non-fmt-panics` lint
+#[rustc_diagnostic_item = "panic_str"]
 #[rustc_const_unstable(feature = "core_panic", issue = "none")]
 pub const fn panic_str(expr: &str) -> ! {
     panic_display(&expr);
 }
 
+#[cfg(not(bootstrap))]
+#[inline]
+#[track_caller]
+#[rustc_diagnostic_item = "unreachable_display"] // needed for `non-fmt-panics` lint
+pub fn unreachable_display<T: fmt::Display>(x: &T) -> ! {
+    panic_fmt(format_args!("internal error: entered unreachable code: {}", *x));
+}
+
 #[inline]
 #[track_caller]
 #[lang = "panic_display"] // needed for const-evaluated panics

src/test/mir-opt/issue_76432.test.SimplifyComparisonIntegral.diff

@@ -21,7 +21,7 @@
       let mut _19: *const T;               // in scope 0 at $DIR/issue_76432.rs:9:54: 9:68
       let mut _20: *const T;               // in scope 0 at $DIR/issue_76432.rs:9:70: 9:84
       let mut _21: *const T;               // in scope 0 at $DIR/issue_76432.rs:9:70: 9:84
-      let mut _22: !;                      // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+      let mut _22: !;                      // in scope 0 at $SRC_DIR/core/src/panic.rs:LL:COL
       let mut _23: &[T; 3];                // in scope 0 at $DIR/issue_76432.rs:7:19: 7:29
       scope 1 {
           debug v => _2;                   // in scope 1 at $DIR/issue_76432.rs:7:9: 7:10
@@ -66,16 +66,16 @@
       }
 
       bb1: {
-          StorageLive(_22);                // scope 1 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
-          core::panicking::panic(const "internal error: entered unreachable code"); // scope 1 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+          StorageLive(_22);                // scope 1 at $SRC_DIR/core/src/panic.rs:LL:COL
+          core::panicking::panic(const "internal error: entered unreachable code"); // scope 1 at $SRC_DIR/core/src/panic.rs:LL:COL
                                            // mir::Constant
-                                           // + span: $SRC_DIR/core/src/macros/mod.rs:LL:COL
+                                           // + span: $SRC_DIR/core/src/panic.rs:LL:COL
                                            // + literal: Const { ty: fn(&'static str) -> ! {core::panicking::panic}, val: Value(Scalar(<ZST>)) }
                                            // ty::Const
                                            // + ty: &str
                                            // + val: Value(Slice { data: Allocation { bytes: [105, 110, 116, 101, 114, 110, 97, 108, 32, 101, 114, 114, 111, 114, 58, 32, 101, 110, 116, 101, 114, 101, 100, 32, 117, 110, 114, 101, 97, 99, 104, 97, 98, 108, 101, 32, 99, 111, 100, 101], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1099511627775], len: Size { raw: 40 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 40 })
                                            // mir::Constant
-                                           // + span: $SRC_DIR/core/src/macros/mod.rs:LL:COL
+                                           // + span: $SRC_DIR/core/src/panic.rs:LL:COL
                                            // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [105, 110, 116, 101, 114, 110, 97, 108, 32, 101, 114, 114, 111, 114, 58, 32, 101, 110, 116, 101, 114, 101, 100, 32, 117, 110, 114, 101, 97, 99, 104, 97, 98, 108, 101, 32, 99, 111, 100, 101], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1099511627775], len: Size { raw: 40 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 40 }) }
       }