Forward formatter settings to bounds of Range<T> in fmt::Debug impl

[LukasKalbertodt]

Before this change, formatter settings were lost when printing a Range. For example, printing a Range<f32> with {:.2?} would not apply the precision modifier when printing the floats. Now the Debug impls look a bit more verbose, but modifier are not lost.

---

I assume the exact output of Debug impls in std cannot be relied on by users and thus can change, right?

[rust-highfive]

r? @Kimundi

(rust_highfive has picked a reviewer for you, use r? to override)

[rust-highfive]

The job x86_64-gnu-llvm-6.0 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.

travis_time:end:180ab87c:start=1554079212009955415,finish=1554079286697164364,duration=74687208949
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
Setting environment variables from .travis.yml
---
[01:16:54] diff of stderr:
[01:16:54] 
[01:16:54] 26   --> $DIR/ub-enum.rs:38:1
[01:16:54] 27    |
[01:16:54] 28 LL | const BAD_ENUM4: Wrap<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out2 };
[01:16:54] -    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected something that cannot possibly fail to be in the range 2..=2
[01:16:54] +    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected something that cannot possibly fail to be in the range 2"..="2
[01:16:54] 30    |
[01:16:54] 31    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
[01:16:54] 
[01:16:54] 
[01:16:54] The actual stderr differed from the expected stderr.
[01:16:54] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/const-eval/ub-enum/ub-enum.stderr
[01:16:54] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/const-eval/ub-enum/ub-enum.stderr
[01:16:54] To update references, rerun the tests and pass the `--bless` flag
[01:16:54] To only update this specific test, also pass `--test-args consts/const-eval/ub-enum.rs`
[01:16:54] error: 1 errors occurred comparing output.
[01:16:54] status: exit code: 1
[01:16:54] status: exit code: 1
[01:16:54] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/consts/const-eval/ub-enum.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/const-eval/ub-enum/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/ui/consts/const-eval/ub-enum/auxiliary" "-A" "unused"
[01:16:54] ------------------------------------------
[01:16:54] 
[01:16:54] ------------------------------------------
[01:16:54] stderr:
[01:16:54] stderr:
[01:16:54] ------------------------------------------
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-enum.rs","byte_start":241,"byte_end":306,"line_start":14,"line_end":14,"column_start":1,"column_end":66,"is_primary":true,"text":[{"text":"const BAD_ENUM: Enum = unsafe { TransmuteEnum { in1: &1 }.out1 };","highlight_start":1,"highlight_end":66}],"label":"type validation failed: encountered a pointer, but expected a valid enum discriminant","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-enum.rs:14:1\n   |\nLL | const BAD_ENUM: Enum = unsafe { TransmuteEnum { in1: &1 }.out1 };\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected a valid enum discriminant\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-enum.rs","byte_start":722,"byte_end":789,"line_start":34,"line_end":34,"column_start":1,"column_end":68,"is_primary":true,"text":[{"text":"const BAD_ENUM2: Enum2 = unsafe { TransmuteEnum2 { in1: 0 }.out1 };","highlight_start":1,"highlight_end":68}],"label":"type validation failed: encountered 0, but expected a valid enum discriminant","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-enum.rs:34:1\n   |\nLL | const BAD_ENUM2: Enum2 = unsafe { TransmuteEnum2 { in1: 0 }.out1 };\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 0, but expected a valid enum discriminant\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-enum.rs","byte_start":823,"byte_end":891,"line_start":36,"line_end":36,"column_start":1,"column_end":69,"is_primary":true,"text":[{"text":"const BAD_ENUM3: Enum2 = unsafe { TransmuteEnum2 { in2: &0 }.out1 };","highlight_start":1,"highlight_end":69}],"label":"type validation failed: encountered a pointer, but expected a valid enum discriminant","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-enum.rs:36:1\n   |\nLL | const BAD_ENUM3: Enum2 = unsafe { TransmuteEnum2 { in2: &0 }.out1 };\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected a valid enum discriminant\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-enum.rs","byte_start":925,"byte_end":999,"line_start":38,"line_end":38,"column_start":1,"column_end":75,"is_primary":true,"text":[{"text":"const BAD_ENUM4: Wrap<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out2 };","highlight_start":1,"highlight_end":75}],"label":"type validation failed: encountered a pointer, but expected something that cannot possibly fail to be in the range 2\"..=\"2","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-enum.rs:38:1\n   |\nLL | const BAD_ENUM4: Wrap<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out2 };\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected something that cannot possibly fail to be in the range 2\"..=\"2\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-enum.rs","byte_start":1062,"byte_end":1136,"line_start":42,"line_end":42,"column_start":1,"column_end":75,"is_primary":true,"text":[{"text":"const BAD_ENUM_UNDEF : Enum2 = unsafe { TransmuteEnum2 { in3: () }.out1 };","highlight_start":1,"highlight_end":75}],"label":"type validation failed: encountered uninitialized bytes, but expected a valid enum discriminant","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-enum.rs:42:1\n   |\nLL | const BAD_ENUM_UNDEF : Enum2 = unsafe { TransmuteEnum2 { in3: () }.out1 };\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized bytes, but expected a valid enum discriminant\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-enum.rs","byte_start":1232,"byte_end":1311,"line_start":46,"line_end":46,"column_start":1,"column_end":80,"is_primary":true,"text":[{"text":"const BAD_ENUM_PTR: Option<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out3 };","highlight_start":1,"highlight_end":80}],"label":"type validation failed: encountered a pointer, but expected a valid enum discriminant","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-enum.rs:46:1\n   |\nLL | const BAD_ENUM_PTR: Option<Enum2> = unsafe { TransmuteEnum2 { in2: &0 }.out3 };\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered a pointer, but expected a valid enum discriminant\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-enum.rs","byte_start":1580,"byte_end":1674,"line_start":56,"line_end":56,"column_start":1,"column_end":95,"is_primary":true,"text":[{"text":"const BAD_ENUM_CHAR: Option<(char, char)> = Some(('x', unsafe { TransmuteChar { a: !0 }.b }));","highlight_start":1,"highlight_end":95}],"label":"type validation failed: encountered 4294967295 at .<downcast-variant(Some)>.0.1, but expected something less or equal to 1114111","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-enum.rs:56:1\n   |\nLL | const BAD_ENUM_CHAR: Option<(char, char)> = Some(('x', unsafe { TransmuteChar { a: !0 }.b }));\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 4294967295 at .<downcast-variant(Some)>.0.1, but expected something less or equal to 1114111\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"For more information about this error, try `rustc --explain E0080`.","code":null,"level":"","spans":[],"children":[],"rendered":"For more information about this error, try `rustc --explain E0080`.\n"}
[01:16:54] 
[01:16:54] ------------------------------------------
[01:16:54] 
---
[01:16:54] diff of stderr:
[01:16:54] 
[01:16:54] 34   --> $DIR/ub-nonnull.rs:28:1
[01:16:54] 35    |
[01:16:54] 36 LL | const BAD_RANGE1: RestrictedRange1 = unsafe { RestrictedRange1(42) };
[01:16:54] -    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 42, but expected something in the range 10..=30
[01:16:54] +    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 42, but expected something in the range 10"..="30
[01:16:54] 38    |
[01:16:54] 39    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior
[01:16:54] 
[01:16:54] 
[01:16:54] The actual stderr differed from the expected stderr.
[01:16:54] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/const-eval/ub-nonnull/ub-nonnull.stderr
[01:16:54] Actual stderr saved to /checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/const-eval/ub-nonnull/ub-nonnull.stderr
[01:16:54] To update references, rerun the tests and pass the `--bless` flag
[01:16:54] To only update this specific test, also pass `--test-args consts/const-eval/ub-nonnull.rs`
[01:16:54] error: 1 errors occurred comparing output.
[01:16:54] status: exit code: 1
[01:16:54] status: exit code: 1
[01:16:54] command: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/src/test/ui/consts/const-eval/ub-nonnull.rs" "-Zthreads=1" "--target=x86_64-unknown-linux-gnu" "--error-format" "json" "-Zui-testing" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/consts/const-eval/ub-nonnull/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/ui/consts/const-eval/ub-nonnull/auxiliary" "-A" "unused"
[01:16:54] ------------------------------------------
[01:16:54] 
[01:16:54] ------------------------------------------
[01:16:54] stderr:
[01:16:54] stderr:
[01:16:54] ------------------------------------------
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-nonnull.rs","byte_start":200,"byte_end":264,"line_start":8,"line_end":8,"column_start":1,"column_end":65,"is_primary":true,"text":[{"text":"const NULL_PTR: NonNull<u8> = unsafe { mem::transmute(0usize) };","highlight_start":1,"highlight_end":65}],"label":"type validation failed: encountered 0, but expected something greater or equal to 1","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-nonnull.rs:8:1\n   |\nLL | const NULL_PTR: NonNull<u8> = unsafe { mem::transmute(0usize) };\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 0, but expected something greater or equal to 1\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-nonnull.rs","byte_start":320,"byte_end":378,"line_start":11,"line_end":11,"column_start":1,"column_end":59,"is_primary":true,"text":[{"text":"const NULL_U8: NonZeroU8 = unsafe { mem::transmute(0u8) };","highlight_start":1,"highlight_end":59}],"label":"type validation failed: encountered 0, but expected something greater or equal to 1","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-nonnull.rs:11:1\n   |\nLL | const NULL_U8: NonZeroU8 = unsafe { mem::transmute(0u8) };\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 0, but expected something greater or equal to 1\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-nonnull.rs","byte_start":433,"byte_end":500,"line_start":13,"line_end":13,"column_start":1,"column_end":68,"is_primary":true,"text":[{"text":"const NULL_USIZE: NonZeroUsize = unsafe { mem::transmute(0usize) };","highlight_start":1,"highlight_end":68}],"label":"type validation failed: encountered 0, but expected something greater or equal to 1","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-nonnull.rs:13:1\n   |\nLL | const NULL_USIZE: NonZeroUsize = unsafe { mem::transmute(0usize) };\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 0, but expected something greater or equal to 1\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-nonnull.rs","byte_start":612,"byte_end":678,"line_start":20,"line_end":20,"column_start":1,"column_end":67,"is_primary":true,"text":[{"text":"const UNINIT: NonZeroU8 = unsafe { Transmute { uninit: () }.out };","highlight_start":1,"highlight_end":67}],"label":"type validation failed: encountered uninitialized bytes, but expected something greater or equal to 1","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-nonnull.rs:20:1\n   |\nLL | const UNINIT: NonZeroU8 = unsafe { Transmute { uninit: () }.out };\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered uninitialized bytes, but expected something greater or equal to 1\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-nonnull.rs","byte_start":918,"byte_end":987,"line_start":28,"line_end":28,"column_start":1,"column_end":70,"is_primary":true,"text":[{"text":"const BAD_RANGE1: RestrictedRange1 = unsafe { RestrictedRange1(42) };","highlight_start":1,"highlight_end":70}],"label":"type validation failed: encountered 42, but expected something in the range 10\"..=\"30","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-nonnull.rs:28:1\n   |\nLL | const BAD_RANGE1: RestrictedRange1 = unsafe { RestrictedRange1(42) };\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 42, but expected something in the range 10\"..=\"30\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"it is undefined behavior to use this value","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":"/checkout/src/test/ui/consts/const-eval/ub-nonnull.rs","byte_start":1161,"byte_end":1230,"line_start":34,"line_end":34,"column_start":1,"column_end":70,"is_primary":true,"text":[{"text":"const BAD_RANGE2: RestrictedRange2 = unsafe { RestrictedRange2(20) };","highlight_start":1,"highlight_end":70}],"label":"type validation failed: encountered 20, but expected something less or equal to 10, or greater or equal to 30","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0080]: it is undefined behavior to use this value\n  --> /checkout/src/test/ui/consts/const-eval/ub-nonnull.rs:34:1\n   |\nLL | const BAD_RANGE2: RestrictedRange2 = unsafe { RestrictedRange2(20) };\n   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ type validation failed: encountered 20, but expected something less or equal to 10, or greater or equal to 30\n   |\n   = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rust compiler repository if you believe it should not be considered undefined behavior\n\n"}
[01:16:54] {"message":"For more information about this error, try `rustc --explain E0080`.","code":null,"level":"","spans":[],"children":[],"rendered":"For more information about this error, try `rustc --explain E0080`.\n"}
[01:16:54] 
[01:16:54] ------------------------------------------
[01:16:54] 
---
[01:16:54] 
[01:16:54] thread 'main' panicked at 'Some tests failed', src/tools/compiletest/src/main.rs:516:22
[01:16:54] 
[01:16:54] 
[01:16:54] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/compiletest" "--compile-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib" "--run-lib-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib" "--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--src-base" "/checkout/src/test/ui" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "ui" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-6.0/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--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" "6.0.0\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
[01:16:54] 
[01:16:54] 
[01:16:54] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:16:54] Build completed unsuccessfully in 0:04:35
[01:16:54] Build completed unsuccessfully in 0:04:35
[01:16:54] make: *** [check] Error 1
[01:16:54] Makefile:48: recipe for target 'check' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:20606a60
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Mon Apr  1 01:58:31 UTC 2019

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)

[Kimundi]

You are right that in theory the output of Debug is not stable, though huge breakages can still be an issue in practice. I doubt someone used formatting options on a range despite it not working, and then relied on it though. 😉

And since this seems to be already the same behavior as in, for example, &[T]s Debugimpl, this seems fine to me.

@bors: r+

[bors]

📌 Commit d3d3049 has been approved by Kimundi