Allow panicking with string literal messages inside constants #52011

oli-obk · 2018-07-03T07:50:29Z

cc #51999

we can't implement things like panic!("foo: {}", x) right now because we can't call trait methods (most notably Display::fmt) inside constants. Also most of these impls probably have loops and conditions, so it's messy anyway.

But hey panic!("foo") works at least.

cc @japaric got any test ideas for #![no_std]?

rust-highfive · 2018-07-03T11:00:06Z

The job x86_64-gnu-llvm-3.9 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[00:47:25] .........................i..........................................................................
[00:47:29] ................................................................................................i...
[00:47:33] ....................................................................................................
[00:47:39] ....................................................................................................
[00:47:44] ..............................................................................F.....................
[00:47:55] ....................................................................................................
[00:48:02] ....................................................................................................
[00:48:07] .i..................................................................................................
[00:48:13] i..ii...............................................................................................
---
[00:48:49] ---- [compile-fail] compile-fail/issue-32829.rs stdout ----
[00:48:49] 
[00:48:49] error: compiler panicked
[00:48:49] status: exit code: 101
[00:48:49] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/compile-fail/issue-32829.rs" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/compile-fail/issue-32829/a" "-Crpath" "-O" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/compile-fail/issue-32829/auxiliary" "-A" "unused"
[00:48:49] ------------------------------------------
[00:48:49] 
[00:48:49] ------------------------------------------
[00:48:49] stderr:
[00:48:49] stderr:
[00:48:49] ------------------------------------------
[00:48:49] {"message":"could not evaluate static initializer","code":{"code":"E0080","explanation":"\nThis error indicates that the compiler was unable to sensibly evaluate an\nconstant expression that had to be evaluated. Attempting to divide by 0\nor causing integer overflow are two ways to induce this error. For example:\n\n```compile_fail,E0080\nenumstart":1,"highlight_end":31},{"text":"$ msg , & ( file ! (  ) , line ! (  ) , __rust_unstable_column ! (  ) ) ) } )","highlight_start":1,"highlight_end":78},{"text":"; ( $ msg : expr , ) => ( { panic ! ( $ msg ) } ) ; (","highlight_start":1,"highlight_end":54},{"text":"$ fmt : expr , $ ( $ arg : tt ) + ) => (","highlight_start":1,"highlight_end":41},{"text":"{","highlight_start":1,"highlight_end":2},{"text":"$ crate :: rt :: begin_panic_fmt (","highlight_start":1,"highlight_end":35},{"text":"& format_args ! ( $ fmt , $ ( $ arg ) + ) , & (","highlight_start":1,"highlight_end":48},{"text":"file ! (  ) , line ! (  ) , __rust_unstable_column ! (  ) ) ) } ) ;","highlight_start":1,"highlight_end":68}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}}}],"children":[],"rendered":"error[E0080]: could not evaluate static initializer\n  --> /checkout/src/test/compile-fail/issue-32829.rs:11:22\n   |\nLL | static S : u64 = { { panic!(\"foo\"); 0 } };\n   |                      ^^^^^^^^^^^^^^ the evaluated program panicked at 'foo', /checkout/src/test/compile-fail/issue-32829.rs:11:22\n   |\n   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)\n\n"}
[00:48:49] {"message":"could not evaluate static initializer","code":{"code":"E0080","explanation":"\nThis error indicates that the compiler was unable to sensibly evaluate an\nconstant expression that had to be evaluated. Attempting to divide by 0\nor causing integer overflow are two ways to induce this error. For example:\n\n```compile_fail,E0080\nenum Enum {\n    X = (1 << 500),\n    Y = (1 / 0)\n}\n```\n\nEnsure that the expressions given can be evaluated as the desired integer type.\nSee the FFI section of the Reference for more information about using a custom\ninteger type:\n\nhttps://doc.rust-lang.org/reference.html#ffi-attributes\n"},"level":"error","spans":[{"file_name":"<panic macros>","byte_start":71,"byte_end":175,"line_start":3,"line_end":4,"column_start":1,"column_end":74,"is_primary":false,"text":[{"text":"$ crate :: rt :: begin_panic (","highlight_start":1,"highlight_end":31},{"text":"$ msg , & ( file ! (  ) , line ! (  ) , __rust_unstable_column ! (  ) ) ) } )","highlight_start":1,"highlight_end":74}],"label":"the evaluated program panicked at 'foo', /checkout/src/test/compile-fail/issue-32829.rs:11:22","suggested_replacement":null,"suggestion_applicability":null,"expansion":{"span":{"file_name":"/checkout/src/test/compile-fail/issue-32829.rs","byte_start":488,"byte_end":502,"line_start":11,"line_end":11,"column_start":22,"column_end":36,"is_primary":false,"text":[{"text":"static S : u64 = { { panic!(\"foo\"); 0 } };","highlight_start":22,"highlight_end":36}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null},"macro_decl_name":"panic!","def_site_span":{"file_name":"<panic macros>","byte_start":0,"byte_end":427,"line_start":1,"line_end":10,"column_start":1,"column_end":68,"is_primary":false,"text":[{"text":"(  ) => ( { panic ! ( \"explicit panic\" ) } ) ; ( $ msg : expr ) => (","highlight_start":1,"highlight_end":69},{"text":"{","highlight_start":1,"highlight_end":2},{"text":"$ crate :: rt :: begin_panic (","highlight_start":1,"highlight_end":31},{"text":"$ msg , & ( file ! (  ) , line ! (  ) , __rust_unstable_column ! (  ) ) ) } )","highlight_start":1,"highlight_end":78},{"text":"; ( $ msg : expr , ) => ( { panic ! ( $ msg ) } ) ; (","highlight_start":1,"highlight_end":54},{"text":"$ fmt : expr , $ ( $ arg : tt ) + ) => (","highlight_start":1,"highlight_end":41},{"text":"{","highlight_start":1,"highlight_end":2},{"text":"$ crate :: rt :: begin_panic_fmt (","highlight_start":1,"highlight_end":35},{"text":"& format_args ! ( $ fmt , $ ( $ arg ) + ) , & (","highlight_start":1,"highlight_end":48},{"text":"file ! (  ) , line ! (  ) , __rust_unstable_column ! (  ) ) ) } ) ;","highlight_start":1,"highlight_end":68}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}}},{"file_name":"/checkout/src/test/compile-fail/issue-32829.rs","byte_start":467,"byte_end":509,"line_start":11,"line_end":11,"column_start":1,"column_end":43,"is_primary":true,"text":[{"text":"static S : u64 = { { panic!(\"foo\"); 0 } };","highlight_start":1,"highlight_end":43}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":"error[E0080]: could not evaluate static initializer\n  --> /checkout/src/test/compile-fail/issue-32829.rs:11:1\n   |\nLL | static S : u64 = { { panic!(\"foo\"); 0 } };\n   | ^^^^^^^^^^^^^^^^^^^^^--------------^^^^^^^\n   |                      |\n   |                      the evaluated program panicked at 'foo', /checkout/src/test/compile-fail/issue-32829.rs:11:22\n   |\n   = note: this error originates in a macro outside of the current crate (in Nightly buiown-linux-gnu" "--mode" "compile-fail" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-3.9/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Zunstable-options " "--target-rustcflags" "-Crpath -O -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--docck-python" "/usr/bin/python2.7" "--lldb-python" "/usr/bin/python2.7" "--gdb" "/usr/bin/gdb" "--quiet" "--llvm-version" "3.9.1\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
[00:48:49] 
[00:48:49] 
[00:48:49] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[00:48:49] Build completed unsuccessfully in 0:12:24
[00:48:49] Build completed unsuccessfully in 0:12:24
[00:48:49] Makefile:58: recipe for target 'check' failed
[00:48:49] make: *** [check] Error 1
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:003a9da0
travis_time:start:003a9da0
$ head -30 ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
head: cannot open ‘./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers’ for reading: No such file or directory
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:00ddf536
$ dmesg | grep -i kill

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

oli-obk · 2018-07-03T11:35:02Z

lol... uhm... there's a if line.contains(" panicked at ") { check in compiletest. Since my error message contains that, the check thinks that rustc panicked.

This seems very fragile (like if an --explain test message contained that).

rust-highfive · 2018-07-03T13:56:56Z

The job x86_64-gnu-llvm-3.9 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[01:17:06] travis_fold:start:test_stage1-std
travis_time:start:test_stage1-std
Testing std stage1 (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:17:07]    Compiling std v0.0.0 (file:///checkout/src/libstd)
[01:17:11] error[E0152]: duplicate lang item found: `begin_panic`.
[01:17:11]     |
[01:17:11]     |
[01:17:11] 402 | / pub fn begin_panic<M: Any + Send>(msg: M, file_line_col: &(&'static str, u32, u32)) -> ! {
[01:17:11] 403 | |     // Note that this should be the only allocation performed in this code path.
[01:17:11] 404 | |     // Currently this means that panic!() on OOM will invoke this code path,
[01:17:11] 405 | |     // but then again we're not really ready for panic on OOM anyway. If
[01:17:11] 437 | |     }
[01:17:11] 438 | | }
[01:17:11]     | |_^
[01:17:11]     |
[01:17:11]     |
[01:17:11]     = note: first defined in crate `std`.
[01:17:11] error: aborting due to previous error
[01:17:11] 
[01:17:11] For more information about this error, try `rustc --explain E0152`.
[01:17:11] error: Could not compile `std`.
[01:17:11] error: Could not compile `std`.
[01:17:11] 
[01:17:11] To learn more, run the command again with --verbose.
[01:17:11] 
[01:17:11] 
[01:17:11] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind jemalloc backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-p" "std" "--" "--quiet"
[01:17:11] 
[01:17:11] 
[01:17:11] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:17:11] Build completed unsuccessfully in 0:34:12
[01:17:11] Build completed unsuccessfully in 0:34:12
[01:17:11] Makefile:58: recipe for target 'check' failed
[01:17:11] make: *** [check] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0fc58b90
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
---
travis_time:end:03730400:start=1530626213106057275,finish=1530626213113776165,duration=7718890
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:0fd23154
$ head -30 ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
head: cannot open ‘./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers’ for reading: No such file or directory
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:0f39f84f
$ dmesg | grep -i kill

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

japaric · 2018-07-05T19:44:18Z

@oli-obk I would test this both in rlib context and in binary context as the later requires the panic_impl lang item. The tests would look like this:

#![no_std]
#![crate_type = "lib"]

const Z: () = panic!("cheese");

const Y: () = unreachable!();

const X: () = unimplemented!();

#![crate_type = "bin"]
#![feature(lang_items)]
#![feature(panic_implementation)]
#![no_main]
#![no_std]

use core::panic::PanicInfo;

const Z: () = panic!("cheese");

const Y: () = unreachable!();

const X: () = unimplemented!();

#[lang = "eh_personality"]
fn eh() {}

#[panic_implementation]
fn panic(_info: &PanicInfo) -> ! {
    loop {}
}

core::panic! calls different functions than std::panic! so you may need another lang item.

oli-obk · 2018-07-06T11:38:17Z

core::panic! calls different functions than std::panic! so you may need another lang item.

I already had it implemented. I just failed at building the test cases

rust-highfive · 2018-07-06T11:52:34Z

The job x86_64-gnu-llvm-3.9 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.


[00:03:37] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:03:37] tidy error: /checkout/src/test/ui/const-eval/const_panic_libcore_main.rs: missing trailing newline
[00:03:37] tidy error: /checkout/src/test/ui/const-eval/const_panic_libcore.rs: missing trailing newline
[00:03:38] some tidy checks failed
[00:03:38] 
[00:03:38] 
[00:03:38] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:03:38] 
[00:03:38] 
[00:03:38] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:03:38] Build completed unsuccessfully in 0:00:47
[00:03:38] Build completed unsuccessfully in 0:00:47
[00:03:38] Makefile:79: recipe for target 'tidy' failed
[00:03:38] make: *** [tidy] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:0a6a4fda
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
---
travis_time:end:0de69f3e:start=1530877447332960667,finish=1530877447340223048,duration=7262381
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:00e7a509
$ head -30 ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
head: cannot open ‘./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers’ for reading: No such file or directory
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:1ba04810
$ dmesg | grep -i kill

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

rust-highfive · 2018-07-06T12:57:02Z

The job x86_64-gnu-llvm-3.9 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[00:57:01] ........................i...........................................................................
[00:57:06] ...............................................................................................i....
[00:57:10] ....................................................................................................
[00:57:17] ....................................................................................................
[00:57:23] .............................................................................F......................
[00:57:36] ....................................................................................................
[00:57:45] ....................................................................................................
[00:57:50] i..................................................................................................i
[00:57:57] ..ii................................................................................................
---
[00:58:41] error: /checkout/src/test/compile-fail/issue-32829.rs:11: expected error not found: could not evaluate static initializer
[00:58:41] 
[00:58:41] error: 0 unexpected errors found, 1 expected errors not found
[00:58:41] status: exit code: 101
[00:58:41] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/compile-fail/issue-32829.rs" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/compile-fail/issue-32829/a" "-Crpath" "-O" "-Zunstable-options" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/compile-fail/issue-32829/auxiliary" "-A" "unused"
[00:58:41]     Error {
[00:58:41]         line_num: 11,
[00:58:41]         kind: Some(
[00:58:41]             Error
[00:58:41]             Error
[00:58:41]         ),
[00:58:41]         msg: "could not evaluate static initializer"
[00:58:41] ]
[00:58:41] 
[00:58:41] 
[00:58:41] thread '[compile-fail] compile-fail/issue-32829.rs' panicked at 'explicit panic', tools/cndroid-cross-path" "" "--color" "always"
[00:58:41] 
[00:58:41] 
[00:58:41] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[00:58:41] Build completed unsuccessfully in 0:14:55
[00:58:41] Build completed unsuccessfully in 0:14:55
[00:58:41] Makefile:58: recipe for target 'check' failed
[00:58:41] make: *** [check] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:22a8c3ec
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

bors · 2018-07-11T18:37:29Z

☔ The latest upstream changes (presumably #51702) made this pull request unmergeable. Please resolve the merge conflicts.

eddyb · 2018-07-12T05:13:15Z

src/librustc/mir/interpret/error.rs

+        msg: String,
+        line: u32,
+        col: u32,
+        file: String,


You want to use Symbol for msg and file.

eddyb · 2018-07-12T05:13:45Z

src/librustc_mir/interpret/const_eval.rs

+        let len = len.to_bits(ecx.memory.pointer_size())?;
+        let bytes = ecx.memory.read_bytes(ptr, Size::from_bytes(len as u64))?;
+        let str = ::std::str::from_utf8(bytes).map_err(|err| EvalErrorKind::ValidationFailure(err.to_string()))?;
+        Ok(str.to_string())


... and intern to Symbol here, without allocating a copy of the string slice!

Oh, because the original value also came from a symbol? Or for making cloning the error cheap?

eddyb · 2018-07-12T05:14:18Z

src/librustc_mir/interpret/const_eval.rs

+    }
+}
+
+fn to_num<'a, 'tcx, 'mir>(


This could be named to_u32.

eddyb · 2018-07-12T05:16:24Z

src/test/ui/const-eval/const_panic_libcore.rs

+#![no_std]
+#![crate_type = "lib"]
+
+const Z: () = panic!("cheese");


This appears to require no feature-gate - I don't think this should be insta-stable. Or is it impossible to feature-gate because panic! has allow_internal_unstable?

Curious. I should be able to work around this easily. Maybe const stability of const fns should not be allowed to be circumvented by rustc macros?

I tried. I have no idea how this test is still passing. We seem to be having a stability hole.

eddyb · 2018-07-12T05:18:26Z

src/test/ui/const-eval/const_panic_libcore.stderr

+LL | const Z: () = panic!("cheese");
+   | ^^^^^^^^^^^^^^----------------^
+   |               |
+   |               evaluated panic invocation 'cheese', $DIR/const_panic_libcore.rs:14:15


"evaluated" doesn't feel right in user output. Maybe mimick the runtime output and say:

panicked at 'cheese', $DIR/const_panic_libcore.rs:14:15

I had that. Our test suite is not able to cope with that because it greps for panicked at and reports a compiler panic. Once the test suite is adjusted, I can fix the message

Maybe something like const panic at 'cheese' instead?

Why not just change the test suite to search for ' panicked at ', i.e. take advantage of the fact that there should be a non-space character before the space before "panicked"?

Once #52197 is merged we don't need any more text hacks. I'll just wait for that

eddyb · 2018-07-12T05:19:40Z

cc @alexcrichton @nikomatsakis on #52011 (comment) (insta-stable feature)

kennytm · 2018-07-14T21:36:01Z

(For easy checking: this PR is blocked on #52197.)

bors · 2018-07-15T00:31:07Z

☔ The latest upstream changes (presumably #52318) made this pull request unmergeable. Please resolve the merge conflicts.

oli-obk · 2018-07-19T16:37:59Z

Unblocked and fixed

pietroalbini · 2018-07-23T12:03:32Z

Ping from triage @eddyb! This PR needs your review.

pietroalbini · 2018-07-30T17:14:01Z

Ping from triage! This PR needs a review, can @eddyb or someone else from @rust-lang/compiler review this?

Also @oli-obk, there are a few merge conflicts you should address.

bjorn3 · 2018-08-18T12:06:53Z

Failure log:

[...]
failures:
---- [ui] ui\const-eval\const_panic_libcore_main.rs stdout ----
diff of stderr:
-	error: this constant cannot be used
-	  --> $DIR/const_panic_libcore_main.rs:20:1
-	   |
-	LL | const Z: () = panic!("cheese");
-	   | ^^^^^^^^^^^^^^----------------^
-	   |               |
-	   |               the evaluated program panicked at 'cheese', $DIR/const_panic_libcore_main.rs:20:15
-	   |
-	   = note: #[deny(const_err)] on by default
-	   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+	error: language item required, but not found: `eh_unwind_resume`
11	
-	error: this constant cannot be used
-	  --> $DIR/const_panic_libcore_main.rs:23:1
-	   |
-	LL | const Y: () = unreachable!();
-	   | ^^^^^^^^^^^^^^--------------^
-	   |               |
-	   |               the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic_libcore_main.rs:23:15
-	   |
-	   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
-	
-	error: this constant cannot be used
-	  --> $DIR/const_panic_libcore_main.rs:26:1
-	   |
-	LL | const X: () = unimplemented!();
-	   | ^^^^^^^^^^^^^^----------------^
-	   |               |
-	   |               the evaluated program panicked at 'not yet implemented', $DIR/const_panic_libcore_main.rs:26:15
-	   |
-	   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
-	
-	error: aborting due to 3 previous errors
+	error: aborting due to previous error
33	
34	
The actual stderr differed from the expected stderr.
[...]
stdout:
------------------------------------------
------------------------------------------
stderr:
------------------------------------------
{"message":"language item required, but not found: `eh_unwind_resume`","code":null,"level":"error","spans":[],"children":[],"rendered":"error: language item required, but not found: `eh_unwind_resume`\n\n"}
{"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error\n\n"}
------------------------------------------
thread '[ui] ui\const-eval\const_panic_libcore_main.rs' panicked at 'explicit panic', tools\compiletest\src\runtest.rs:3189:9
note: Run with `RUST_BACKTRACE=1` for a backtrace.
failures:
    [ui] ui\const-eval\const_panic_libcore_main.rs
[...]

bors · 2018-08-19T04:42:14Z

⌛ Testing commit 768ffb714d0ebab8faa9ff6d97307219615016ca with merge 741e7c3c07a2b4a7630b9c35516eec4105991fca...

bors · 2018-08-19T05:32:18Z

💔 Test failed - status-appveyor

kennytm · 2018-08-19T07:52:16Z

A lang item is not defined. Same error as #52011 (comment).

 ---- [ui] ui\const-eval\const_panic_libcore_main.rs stdout ----
 diff of stderr:
-	error: this constant cannot be used
-	  --> $DIR/const_panic_libcore_main.rs:20:1
-	   |
-	LL | const Z: () = panic!("cheese");
-	   | ^^^^^^^^^^^^^^----------------^
-	   |               |
-	   |               the evaluated program panicked at 'cheese', $DIR/const_panic_libcore_main.rs:20:15
-	   |
-	   = note: #[deny(const_err)] on by default
-	   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
+	error: language item required, but not found: `eh_unwind_resume`
11	
-	error: this constant cannot be used
-	  --> $DIR/const_panic_libcore_main.rs:23:1
-	   |
-	LL | const Y: () = unreachable!();
-	   | ^^^^^^^^^^^^^^--------------^
-	   |               |
-	   |               the evaluated program panicked at 'internal error: entered unreachable code', $DIR/const_panic_libcore_main.rs:23:15
-	   |
-	   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
-	
-	error: this constant cannot be used
-	  --> $DIR/const_panic_libcore_main.rs:26:1
-	   |
-	LL | const X: () = unimplemented!();
-	   | ^^^^^^^^^^^^^^----------------^
-	   |               |
-	   |               the evaluated program panicked at 'not yet implemented', $DIR/const_panic_libcore_main.rs:26:15
-	   |
-	   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
-	
-	error: aborting due to 3 previous errors
+	error: aborting due to previous error
33	
34

bors · 2018-08-20T01:21:03Z

☔ The latest upstream changes (presumably #52953) made this pull request unmergeable. Please resolve the merge conflicts.

oli-obk · 2018-08-22T16:32:20Z

rebased and added lang item to test

@bors r=eddyb

bors · 2018-08-22T16:32:21Z

📌 Commit bd6ae6a has been approved by eddyb

RalfJung · 2018-08-22T17:41:25Z

src/librustc_mir/interpret/const_eval.rs

+    } else {
+        bug!("panic arg is not a str")
+    }
+}


We have that same code in miri...^^

bors · 2018-08-22T22:08:09Z

⌛ Testing commit bd6ae6a with merge 917945d...

@eddyb

…anics_constantly, r=eddyb Allow panicking with string literal messages inside constants r? @eddyb cc #51999 we can't implement things like `panic!("foo: {}", x)` right now because we can't call trait methods (most notably `Display::fmt`) inside constants. Also most of these impls probably have loops and conditions, so it's messy anyway. But hey `panic!("foo")` works at least. cc @japaric got any test ideas for `#![no_std]`?

bors · 2018-08-23T00:22:15Z

☀️ Test successful - status-appveyor, status-travis
Approved by: eddyb
Pushing 917945d to master...

rust-highfive assigned eddyb Jul 3, 2018

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oli-obk force-pushed the dont_you_hate_it_too_when_everything_panics_constantly branch from 70760f5 to a26713a Compare July 3, 2018 10:08

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Tracking issue for RFC 2345, "Allow panicking in constants" (const_panic) #51999

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eddyb reviewed Jul 12, 2018

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src/librustc_mir/interpret/const_eval.rs Outdated

}

}

fn to_num<'a, 'tcx, 'mir>(

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This could be named to_u32.

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oli-obk mentioned this pull request Aug 22, 2018

Making enums more specific in src/librustc/mir/interpret/error.rs rust-lang/const-eval#4

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Allow panicking with string literal messages inside constants

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oli-obk force-pushed the dont_you_hate_it_too_when_everything_panics_constantly branch from 768ffb7 to 0db77dd Compare August 22, 2018 16:29

Reexpose stability hole in the presence of feature gates

bd6ae6a

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src/librustc_mir/interpret/const_eval.rs

} else {

bug!("panic arg is not a str")

}

}

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We have that same code in miri...^^

bors merged commit bd6ae6a into rust-lang:master Aug 23, 2018

bors mentioned this pull request Aug 23, 2018

Tidy CFTE/MIRI #53609

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eddyb mentioned this pull request Nov 3, 2018

[WIP] Require specific feature names in #[allow_internal_unstable]. #54714

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Allow panicking with string literal messages inside constants #52011

Allow panicking with string literal messages inside constants #52011

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eddyb commented Jul 12, 2018

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