Auto merge of #102318 - Amanieu:default_alloc_error_handler, r=oli-obk

Stabilize default_alloc_error_handler

Tracking issue: #66741

This turns `feature(default_alloc_error_handler)` on by default, which causes the compiler to automatically generate a default OOM handler which panics if `#[alloc_error_handler]` is not provided.

The FCP completed over 2 years ago but the stabilization was blocked due to an issue with unwinding. This was fixed by #88098 so stabilization can be unblocked.

Closes #66741

4 files changed, 34 insertions, 101 deletions

diff --git a/src/test/ui/allocator/no_std-alloc-error-handler-custom.rs b/src/test/ui/allocator/no_std-alloc-error-handler-custom.rs
index 851da231a73..28926243390 100644
--- a/src/test/ui/allocator/no_std-alloc-error-handler-custom.rs
+++ b/src/test/ui/allocator/no_std-alloc-error-handler-custom.rs
@@ -7,9 +7,10 @@
 // compile-flags:-C panic=abort
 // aux-build:helper.rs
 
-#![feature(start, rustc_private, new_uninit, panic_info_message, lang_items)]
+#![feature(rustc_private, lang_items)]
 #![feature(alloc_error_handler)]
 #![no_std]
+#![no_main]
 
 extern crate alloc;
 extern crate libc;
@@ -21,35 +22,30 @@ pub fn __aeabi_unwind_cpp_pr0() {}
 #[no_mangle]
 pub fn __aeabi_unwind_cpp_pr1() {}
 
-use core::ptr::null_mut;
-use core::alloc::{GlobalAlloc, Layout};
 use alloc::boxed::Box;
+use alloc::string::ToString;
+use core::alloc::{GlobalAlloc, Layout};
+use core::ptr::null_mut;
 
 extern crate helper;
 
 struct MyAllocator;
 
 #[alloc_error_handler]
-fn my_oom(layout: Layout) -> !
-{
+fn my_oom(layout: Layout) -> ! {
     use alloc::fmt::write;
     unsafe {
         let size = layout.size();
         let mut s = alloc::string::String::new();
         write(&mut s, format_args!("My OOM: failed to allocate {} bytes!\n", size)).unwrap();
-        let s = s.as_str();
-        libc::write(libc::STDERR_FILENO, s as *const _ as _, s.len());
+        libc::write(libc::STDERR_FILENO, s.as_ptr() as *const _, s.len());
         libc::exit(0)
     }
 }
 
 unsafe impl GlobalAlloc for MyAllocator {
     unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
-        if layout.size() < 4096 {
-            libc::malloc(layout.size()) as _
-        } else {
-            null_mut()
-        }
+        if layout.size() < 4096 { libc::malloc(layout.size()) as _ } else { null_mut() }
     }
     unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {}
 }
@@ -60,26 +56,12 @@ static A: MyAllocator = MyAllocator;
 #[panic_handler]
 fn panic(panic_info: &core::panic::PanicInfo) -> ! {
     unsafe {
-        if let Some(s) = panic_info.payload().downcast_ref::<&str>() {
-            const PSTR: &str = "panic occurred: ";
-            const CR: &str = "\n";
-            libc::write(libc::STDERR_FILENO, PSTR as *const _ as _, PSTR.len());
-            libc::write(libc::STDERR_FILENO, s as *const _ as _, s.len());
-            libc::write(libc::STDERR_FILENO, CR as *const _ as _, CR.len());
-        }
-        if let Some(args) = panic_info.message() {
-            let mut s = alloc::string::String::new();
-            alloc::fmt::write(&mut s, *args).unwrap();
-            let s = s.as_str();
-            const PSTR: &str = "panic occurred: ";
-            const CR: &str = "\n";
-            libc::write(libc::STDERR_FILENO, PSTR as *const _ as _, PSTR.len());
-            libc::write(libc::STDERR_FILENO, s as *const _ as _, s.len());
-            libc::write(libc::STDERR_FILENO, CR as *const _ as _, CR.len());
-        } else {
-            const PSTR: &str = "panic occurred\n";
-            libc::write(libc::STDERR_FILENO, PSTR as *const _ as _, PSTR.len());
-        }
+        let s = panic_info.to_string();
+        const PSTR: &str = "panic occurred: ";
+        const CR: &str = "\n";
+        libc::write(libc::STDERR_FILENO, PSTR.as_ptr() as *const _, PSTR.len());
+        libc::write(libc::STDERR_FILENO, s.as_ptr() as *const _, s.len());
+        libc::write(libc::STDERR_FILENO, CR.as_ptr() as *const _, CR.len());
         libc::exit(1)
     }
 }
@@ -89,15 +71,14 @@ fn panic(panic_info: &core::panic::PanicInfo) -> ! {
 // in these libraries will refer to `rust_eh_personality` if LLVM can not *prove* the contents won't
 // unwind. So, for this test case we will define the symbol.
 #[lang = "eh_personality"]
-extern fn rust_eh_personality() {}
+extern "C" fn rust_eh_personality() {}
 
-#[derive(Debug)]
+#[derive(Default, Debug)]
 struct Page(#[allow(unused_tuple_struct_fields)] [[u64; 32]; 16]);
 
-#[start]
-pub fn main(_argc: isize, _argv: *const *const u8) -> isize {
-    let zero = Box::<Page>::new_zeroed();
-    let zero = unsafe { zero.assume_init() };
+#[no_mangle]
+fn main(_argc: i32, _argv: *const *const u8) -> isize {
+    let zero = Box::<Page>::new(Default::default());
     helper::work_with(&zero);
     1
 }
diff --git a/src/test/ui/allocator/no_std-alloc-error-handler-default.rs b/src/test/ui/allocator/no_std-alloc-error-handler-default.rs
index 30ce0f162c7..56409e71339 100644
--- a/src/test/ui/allocator/no_std-alloc-error-handler-default.rs
+++ b/src/test/ui/allocator/no_std-alloc-error-handler-default.rs
@@ -6,11 +6,10 @@
 // only-linux
 // compile-flags:-C panic=abort
 // aux-build:helper.rs
-// gate-test-default_alloc_error_handler
 
-#![feature(start, rustc_private, new_uninit, panic_info_message, lang_items)]
-#![feature(default_alloc_error_handler)]
+#![feature(rustc_private, lang_items)]
 #![no_std]
+#![no_main]
 
 extern crate alloc;
 extern crate libc;
@@ -23,6 +22,7 @@ pub fn __aeabi_unwind_cpp_pr0() {}
 pub fn __aeabi_unwind_cpp_pr1() {}
 
 use alloc::boxed::Box;
+use alloc::string::ToString;
 use core::alloc::{GlobalAlloc, Layout};
 use core::ptr::null_mut;
 
@@ -32,11 +32,7 @@ struct MyAllocator;
 
 unsafe impl GlobalAlloc for MyAllocator {
     unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
-        if layout.size() < 4096 {
-            libc::malloc(layout.size()) as _
-        } else {
-            null_mut()
-        }
+        if layout.size() < 4096 { libc::malloc(layout.size()) as _ } else { null_mut() }
     }
     unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {}
 }
@@ -47,26 +43,12 @@ static A: MyAllocator = MyAllocator;
 #[panic_handler]
 fn panic(panic_info: &core::panic::PanicInfo) -> ! {
     unsafe {
-        if let Some(s) = panic_info.payload().downcast_ref::<&str>() {
-            const PSTR: &str = "panic occurred: ";
-            const CR: &str = "\n";
-            libc::write(libc::STDERR_FILENO, PSTR as *const _ as _, PSTR.len());
-            libc::write(libc::STDERR_FILENO, s as *const _ as _, s.len());
-            libc::write(libc::STDERR_FILENO, CR as *const _ as _, CR.len());
-        }
-        if let Some(args) = panic_info.message() {
-            let mut s = alloc::string::String::new();
-            alloc::fmt::write(&mut s, *args).unwrap();
-            let s = s.as_str();
-            const PSTR: &str = "panic occurred: ";
-            const CR: &str = "\n";
-            libc::write(libc::STDERR_FILENO, PSTR as *const _ as _, PSTR.len());
-            libc::write(libc::STDERR_FILENO, s as *const _ as _, s.len());
-            libc::write(libc::STDERR_FILENO, CR as *const _ as _, CR.len());
-        } else {
-            const PSTR: &str = "panic occurred\n";
-            libc::write(libc::STDERR_FILENO, PSTR as *const _ as _, PSTR.len());
-        }
+        let s = panic_info.to_string();
+        const PSTR: &str = "panic occurred: ";
+        const CR: &str = "\n";
+        libc::write(libc::STDERR_FILENO, PSTR.as_ptr() as *const _, PSTR.len());
+        libc::write(libc::STDERR_FILENO, s.as_ptr() as *const _, s.len());
+        libc::write(libc::STDERR_FILENO, CR.as_ptr() as *const _, CR.len());
         libc::exit(0)
     }
 }
@@ -76,15 +58,14 @@ fn panic(panic_info: &core::panic::PanicInfo) -> ! {
 // in these libraries will refer to `rust_eh_personality` if LLVM can not *prove* the contents won't
 // unwind. So, for this test case we will define the symbol.
 #[lang = "eh_personality"]
-extern fn rust_eh_personality() {}
+extern "C" fn rust_eh_personality() {}
 
-#[derive(Debug)]
+#[derive(Default, Debug)]
 struct Page(#[allow(unused_tuple_struct_fields)] [[u64; 32]; 16]);
 
-#[start]
-pub fn main(_argc: isize, _argv: *const *const u8) -> isize {
-    let zero = Box::<Page>::new_zeroed();
-    let zero = unsafe { zero.assume_init() };
+#[no_mangle]
+fn main(_argc: i32, _argv: *const *const u8) -> isize {
+    let zero = Box::<Page>::new(Default::default());
     helper::work_with(&zero);
     1
 }
diff --git a/src/test/ui/missing/missing-alloc_error_handler.rs b/src/test/ui/missing/missing-alloc_error_handler.rs
deleted file mode 100644
index 4d378f010ed..00000000000
--- a/src/test/ui/missing/missing-alloc_error_handler.rs
+++ /dev/null
@@ -1,23 +0,0 @@
-// compile-flags: -C panic=abort
-// no-prefer-dynamic
-
-#![no_std]
-#![crate_type = "staticlib"]
-#![feature(alloc_error_handler)]
-
-#[panic_handler]
-fn panic(_: &core::panic::PanicInfo) -> ! {
-    loop {}
-}
-
-extern crate alloc;
-
-#[global_allocator]
-static A: MyAlloc = MyAlloc;
-
-struct MyAlloc;
-
-unsafe impl core::alloc::GlobalAlloc for MyAlloc {
-    unsafe fn alloc(&self, _: core::alloc::Layout) -> *mut u8 { 0 as _ }
-    unsafe fn dealloc(&self, _: *mut u8, _: core::alloc::Layout) {}
-}
diff --git a/src/test/ui/missing/missing-alloc_error_handler.stderr b/src/test/ui/missing/missing-alloc_error_handler.stderr
deleted file mode 100644
index 995fa7cf85e..00000000000
--- a/src/test/ui/missing/missing-alloc_error_handler.stderr
+++ /dev/null
@@ -1,6 +0,0 @@
-error: `#[alloc_error_handler]` function required, but not found
-
-note: use `#![feature(default_alloc_error_handler)]` for a default error handler
-
-error: aborting due to previous error
-