Auto merge of #50338 - japaric:panic-impl, r=alexcrichton

implement #[panic_implementation]

This implements the `#[panic_implementation]` attribute as instructed in #44489 (comment)

I haven't run the full test suite yet but at least all the compile-fail tests pass.

r? @nagisa

Author: bors

src/doc/unstable-book/src/language-features/lang-items.md

@@ -19,6 +19,7 @@ sugar for dynamic allocations via `malloc` and `free`:
 #![feature(lang_items, box_syntax, start, libc, core_intrinsics)]
 #![no_std]
 use core::intrinsics;
+use core::panic::PanicInfo;
 
 extern crate libc;
 
@@ -50,7 +51,7 @@ fn main(_argc: isize, _argv: *const *const u8) -> isize {
 }
 
 #[lang = "eh_personality"] extern fn rust_eh_personality() {}
-#[lang = "panic_fmt"] extern fn rust_begin_panic() -> ! { unsafe { intrinsics::abort() } }
+#[lang = "panic_impl"] extern fn rust_begin_panic(info: &PanicInfo) -> ! { unsafe { intrinsics::abort() } }
 #[lang = "eh_unwind_resume"] extern fn rust_eh_unwind_resume() {}
 #[no_mangle] pub extern fn rust_eh_register_frames () {}
 #[no_mangle] pub extern fn rust_eh_unregister_frames () {}
@@ -110,6 +111,7 @@ in the same format as C:
 #![feature(start)]
 #![no_std]
 use core::intrinsics;
+use core::panic::PanicInfo;
 
 // Pull in the system libc library for what crt0.o likely requires.
 extern crate libc;
@@ -134,12 +136,9 @@ pub extern fn rust_eh_personality() {
 pub extern fn rust_eh_unwind_resume() {
 }
 
-#[lang = "panic_fmt"]
+#[lang = "panic_impl"]
 #[no_mangle]
-pub extern fn rust_begin_panic(_msg: core::fmt::Arguments,
-                               _file: &'static str,
-                               _line: u32,
-                               _column: u32) -> ! {
+pub extern fn rust_begin_panic(info: &PanicInfo) -> ! {
     unsafe { intrinsics::abort() }
 }
 ```
@@ -155,6 +154,7 @@ compiler's name mangling too:
 #![no_std]
 #![no_main]
 use core::intrinsics;
+use core::panic::PanicInfo;
 
 // Pull in the system libc library for what crt0.o likely requires.
 extern crate libc;
@@ -179,12 +179,9 @@ pub extern fn rust_eh_personality() {
 pub extern fn rust_eh_unwind_resume() {
 }
 
-#[lang = "panic_fmt"]
+#[lang = "panic_impl"]
 #[no_mangle]
-pub extern fn rust_begin_panic(_msg: core::fmt::Arguments,
-                               _file: &'static str,
-                               _line: u32,
-                               _column: u32) -> ! {
+pub extern fn rust_begin_panic(info: &PanicInfo) -> ! {
     unsafe { intrinsics::abort() }
 }
 ```
@@ -215,7 +212,7 @@ called. The language item's name is `eh_personality`.
 
 The second function, `rust_begin_panic`, is also used by the failure mechanisms of the
 compiler. When a panic happens, this controls the message that's displayed on
-the screen. While the language item's name is `panic_fmt`, the symbol name is
+the screen. While the language item's name is `panic_impl`, the symbol name is
 `rust_begin_panic`.
 
 A third function, `rust_eh_unwind_resume`, is also needed if the `custom_unwind_resume`
@@ -259,8 +256,8 @@ the source code.
   - `msvc_try_filter`: `libpanic_unwind/seh.rs` (SEH)
   - `panic`: `libcore/panicking.rs`
   - `panic_bounds_check`: `libcore/panicking.rs`
-  - `panic_fmt`: `libcore/panicking.rs`
-  - `panic_fmt`: `libstd/panicking.rs`
+  - `panic_impl`: `libcore/panicking.rs`
+  - `panic_impl`: `libstd/panicking.rs`
 - Allocations
   - `owned_box`: `liballoc/boxed.rs`
   - `exchange_malloc`: `liballoc/heap.rs`

src/doc/unstable-book/src/language-features/used.md

@@ -87,11 +87,13 @@ This condition can be met using `#[used]` and `#[link_section]` plus a linker
 script.
 
 ``` rust,ignore
-#![feature(lang_items)]
+#![feature(panic_implementation)]
 #![feature(used)]
 #![no_main]
 #![no_std]
 
+use core::panic::PanicInfo;
+
 extern "C" fn reset_handler() -> ! {
     loop {}
 }
@@ -100,8 +102,10 @@ extern "C" fn reset_handler() -> ! {
 #[used]
 static RESET_HANDLER: extern "C" fn() -> ! = reset_handler;
 
-#[lang = "panic_fmt"]
-fn panic_fmt() {}
+#[panic_implementation]
+fn panic_impl(info: &PanicInfo) -> ! {
+    loop {}
+}
 ```
 
 ``` text

src/libcore/lib.rs

@@ -41,7 +41,7 @@
 //!   dictate the panic message, the file at which panic was invoked, and the
 //!   line and column inside the file. It is up to consumers of this core
 //!   library to define this panic function; it is only required to never
-//!   return. This requires a `lang` attribute named `panic_fmt`.
+//!   return. This requires a `lang` attribute named `panic_impl`.
 //!
 //! * `rust_eh_personality` - is used by the failure mechanisms of the
 //!    compiler. This is often mapped to GCC's personality function, but crates

src/libcore/panic.rs

@@ -35,6 +35,7 @@ use fmt;
 ///
 /// panic!("Normal panic");
 /// ```
+#[cfg_attr(not(stage0), lang = "panic_info")]
 #[stable(feature = "panic_hooks", since = "1.10.0")]
 #[derive(Debug)]
 pub struct PanicInfo<'a> {
@@ -53,7 +54,8 @@ impl<'a> PanicInfo<'a> {
     pub fn internal_constructor(message: Option<&'a fmt::Arguments<'a>>,
                                 location: Location<'a>)
                                 -> Self {
-        PanicInfo { payload: &(), location, message }
+        struct NoPayload;
+        PanicInfo { payload: &NoPayload, location, message }
     }
 
     #[doc(hidden)]
@@ -121,7 +123,7 @@ impl<'a> PanicInfo<'a> {
     #[stable(feature = "panic_hooks", since = "1.10.0")]
     pub fn location(&self) -> Option<&Location> {
         // NOTE: If this is changed to sometimes return None,
-        // deal with that case in std::panicking::default_hook.
+        // deal with that case in std::panicking::default_hook and std::panicking::begin_panic_fmt.
         Some(&self.location)
     }
 }

src/libcore/panicking.rs

@@ -37,6 +37,8 @@
             issue = "0")]
 
 use fmt;
+#[cfg(not(stage0))]
+use panic::{Location, PanicInfo};
 
 #[cold] #[inline(never)] // this is the slow path, always
 #[lang = "panic"]
@@ -59,6 +61,7 @@ fn panic_bounds_check(file_line_col: &(&'static str, u32, u32),
                            len, index), file_line_col)
 }
 
+#[cfg(stage0)]
 #[cold] #[inline(never)]
 pub fn panic_fmt(fmt: fmt::Arguments, file_line_col: &(&'static str, u32, u32)) -> ! {
     #[allow(improper_ctypes)]
@@ -70,3 +73,21 @@ pub fn panic_fmt(fmt: fmt::Arguments, file_line_col: &(&'static str, u32, u32))
     let (file, line, col) = *file_line_col;
     unsafe { panic_impl(fmt, file, line, col) }
 }
+
+#[cfg(not(stage0))]
+#[cold] #[inline(never)]
+pub fn panic_fmt(fmt: fmt::Arguments, file_line_col: &(&'static str, u32, u32)) -> ! {
+    // NOTE This function never crosses the FFI boundary; it's a Rust-to-Rust call
+    #[allow(improper_ctypes)] // PanicInfo contains a trait object which is not FFI safe
+    extern "Rust" {
+        #[lang = "panic_impl"]
+        fn panic_impl(pi: &PanicInfo) -> !;
+    }
+
+    let (file, line, col) = *file_line_col;
+    let pi = PanicInfo::internal_constructor(
+        Some(&fmt),
+        Location::internal_constructor(file, line, col),
+    );
+    unsafe { panic_impl(&pi) }
+}

src/librustc/diagnostics.rs

@@ -637,8 +637,8 @@ Erroneous code example:
 ```compile_fail,E0152
 #![feature(lang_items)]
 
-#[lang = "panic_fmt"]
-struct Foo; // error: duplicate lang item found: `panic_fmt`
+#[lang = "panic_impl"]
+struct Foo; // error: duplicate lang item found: `panic_impl`
 ```
 
 Lang items are already implemented in the standard library. Unless you are
@@ -824,7 +824,7 @@ A list of available external lang items is available in
 #![feature(lang_items)]
 
 extern "C" {
-    #[lang = "panic_fmt"] // ok!
+    #[lang = "panic_impl"] // ok!
     fn cake();
 }
 ```

src/librustc/middle/dead.rs

@@ -284,7 +284,7 @@ impl<'a, 'tcx> Visitor<'tcx> for MarkSymbolVisitor<'a, 'tcx> {
 fn has_allow_dead_code_or_lang_attr(tcx: TyCtxt,
                                     id: ast::NodeId,
                                     attrs: &[ast::Attribute]) -> bool {
-    if attr::contains_name(attrs, "lang") {
+    if attr::contains_name(attrs, "lang") || attr::contains_name(attrs, "panic_implementation") {
         return true;
     }
 

src/librustc/middle/lang_items.rs

@@ -185,6 +185,8 @@ pub fn extract(attrs: &[ast::Attribute]) -> Option<(Symbol, Span)> {
             if let Some(value) = attribute.value_str() {
                 return Some((value, attribute.span));
             }
+        } else if attribute.check_name("panic_implementation") {
+            return Some((Symbol::intern("panic_impl"), attribute.span))
         }
     }
 
@@ -299,7 +301,8 @@ language_item_table! {
     // lang item, but do not have it defined.
     PanicFnLangItem,                 "panic",                   panic_fn;
     PanicBoundsCheckFnLangItem,      "panic_bounds_check",      panic_bounds_check_fn;
-    PanicFmtLangItem,                "panic_fmt",               panic_fmt;
+    PanicInfoLangItem,               "panic_info",              panic_info;
+    PanicImplLangItem,               "panic_impl",              panic_impl;
 
     ExchangeMallocFnLangItem,        "exchange_malloc",         exchange_malloc_fn;
     BoxFreeFnLangItem,               "box_free",                box_free_fn;

src/librustc/middle/weak_lang_items.rs

@@ -148,7 +148,7 @@ impl<'a, 'tcx, 'v> Visitor<'v> for Context<'a, 'tcx> {
 ) }
 
 weak_lang_items! {
-    panic_fmt,          PanicFmtLangItem,           rust_begin_unwind;
+    panic_impl,         PanicImplLangItem,          rust_begin_unwind;
     eh_personality,     EhPersonalityLangItem,      rust_eh_personality;
     eh_unwind_resume,   EhUnwindResumeLangItem,     rust_eh_unwind_resume;
     oom,                OomLangItem,                rust_oom;

src/librustc_typeck/check/mod.rs

@@ -96,7 +96,7 @@ use rustc::middle::region;
 use rustc::mir::interpret::{GlobalId};
 use rustc::ty::subst::{UnpackedKind, Subst, Substs};
 use rustc::traits::{self, ObligationCause, ObligationCauseCode, TraitEngine};
-use rustc::ty::{self, Ty, TyCtxt, GenericParamDefKind, Visibility, ToPredicate};
+use rustc::ty::{self, Ty, TyCtxt, GenericParamDefKind, Visibility, ToPredicate, RegionKind};
 use rustc::ty::adjustment::{Adjust, Adjustment, AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
 use rustc::ty::fold::TypeFoldable;
 use rustc::ty::maps::Providers;
@@ -130,7 +130,7 @@ use syntax_pos::{self, BytePos, Span, MultiSpan};
 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
 use rustc::hir::itemlikevisit::ItemLikeVisitor;
 use rustc::hir::map::Node;
-use rustc::hir::{self, PatKind};
+use rustc::hir::{self, PatKind, Item_};
 use rustc::middle::lang_items;
 
 mod autoderef;
@@ -1129,6 +1129,60 @@ fn check_fn<'a, 'gcx, 'tcx>(inherited: &'a Inherited<'a, 'gcx, 'tcx>,
         }
     }
 
+    // Check that a function marked as `#[panic_implementation]` has signature `fn(&PanicInfo) -> !`
+    if let Some(panic_impl_did) = fcx.tcx.lang_items().panic_impl() {
+        if panic_impl_did == fn_hir_id.owner_def_id() {
+            if let Some(panic_info_did) = fcx.tcx.lang_items().panic_info() {
+                if declared_ret_ty.sty != ty::TyNever {
+                    fcx.tcx.sess.span_err(
+                        decl.output.span(),
+                        "return type should be `!`",
+                    );
+                }
+
+                let inputs = fn_sig.inputs();
+                let span = fcx.tcx.hir.span(fn_id);
+                if inputs.len() == 1 {
+                    let arg_is_panic_info = match inputs[0].sty {
+                        ty::TyRef(region, ty, mutbl) => match ty.sty {
+                            ty::TyAdt(ref adt, _) => {
+                                adt.did == panic_info_did &&
+                                    mutbl == hir::Mutability::MutImmutable &&
+                                    *region != RegionKind::ReStatic
+                            },
+                            _ => false,
+                        },
+                        _ => false,
+                    };
+
+                    if !arg_is_panic_info {
+                        fcx.tcx.sess.span_err(
+                            decl.inputs[0].span,
+                            "argument should be `&PanicInfo`",
+                        );
+                    }
+
+                    if let Node::NodeItem(item) = fcx.tcx.hir.get(fn_id) {
+                        if let Item_::ItemFn(_, _, _, _, ref generics, _) = item.node {
+                            if !generics.params.is_empty() {
+                                fcx.tcx.sess.span_err(
+                                    span,
+                                    "`#[panic_implementation]` function should have no type \
+                                     parameters",
+                                );
+                            }
+                        }
+                    }
+                } else {
+                    fcx.tcx.sess.span_err(span, "function should have one argument");
+                }
+            } else {
+                fcx.tcx.sess.err("language item required, but not found: `panic_info`");
+            }
+        }
+
+    }
+
     (fcx, gen_ty)
 }