suggest hex escapes for C-style escapes

[euclio]

Fixes #148884.

[rustbot]

The parser was modified, potentially altering the grammar of (stable) Rust
which would be a breaking change.

cc @fmease

[rustbot]

r? @mu001999

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[asquared31415]

I don't think that the "(perhaps transcribing from another language)" part is useful to the diagnostic. It should be clear from context that Rust simply does this differently.

[mu001999]

Thanks! Just some nits

View changes since this review

[mu001999]

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[rust-log-analyzer]

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

##[endgroup]
Executing "/scripts/stage_2_test_set1.sh"
+ /scripts/stage_2_test_set1.sh
+ '[' 1 == 1 ']'
+ echo 'PR_CI_JOB set; skipping tidy'
+ SKIP_TIDY='--skip tidy'
+ ../x.py --stage 2 test --skip tidy --skip compiler --skip src
PR_CI_JOB set; skipping tidy
##[group]Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.04s
##[endgroup]
---

5    |                                ^ unknown byte escape
6    |
7    = help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>
+ help: if you meant to write a form feed, use a hex escape
+    |
+ LL - static FOO: &'static [u8] = b"\f";
+ LL + static FOO: &'static [u8] = b"\x0C";
+    |
8 
9 error: unknown byte escape: `f`
10   --> $DIR/byte-string-literals.rs:4:8

13    |        ^ unknown byte escape
14    |
15    = help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>
+ help: if you meant to write a form feed, use a hex escape
+    |
+ LL -     b"\f";
+ LL +     b"\x0C";
+    |
16 
17 error: invalid character in numeric character escape: `Z`
18   --> $DIR/byte-string-literals.rs:5:10

Note: some mismatched output was normalized before being compared
- LL - static FOO: &'static [u8] = b"\f";  //~ ERROR unknown byte escape
- LL + static FOO: &'static [u8] = b"\\x0C";  //~ ERROR unknown byte escape
- LL -     b"\f";  //~ ERROR unknown byte escape
- LL +     b"\\x0C";  //~ ERROR unknown byte escape
+ help: if you meant to write a form feed, use a hex escape
+    |
+ LL - static FOO: &'static [u8] = b"\f";
+ LL + static FOO: &'static [u8] = b"\x0C";
+    |
+ help: if you meant to write a form feed, use a hex escape
+    |
+ LL -     b"\f";
+ LL +     b"\x0C";
+    |


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args parser/byte-string-literals.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/parser/byte-string-literals.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/parser/byte-string-literals" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error: unknown byte escape: `f`
##[error]  --> /checkout/tests/ui/parser/byte-string-literals.rs:1:32
   |
LL | static FOO: &'static [u8] = b"\f";  //~ ERROR unknown byte escape
   |                                ^ unknown byte escape
   |
   = help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>
help: if you meant to write a form feed, use a hex escape
   |
LL - static FOO: &'static [u8] = b"\f";  //~ ERROR unknown byte escape
LL + static FOO: &'static [u8] = b"\\x0C";  //~ ERROR unknown byte escape
   |

error: unknown byte escape: `f`
##[error]  --> /checkout/tests/ui/parser/byte-string-literals.rs:4:8
   |
LL |     b"\f";  //~ ERROR unknown byte escape
   |        ^ unknown byte escape
   |
   = help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>
help: if you meant to write a form feed, use a hex escape
   |
LL -     b"\f";  //~ ERROR unknown byte escape
LL +     b"\\x0C";  //~ ERROR unknown byte escape
   |

error: invalid character in numeric character escape: `Z`
##[error]  --> /checkout/tests/ui/parser/byte-string-literals.rs:5:10
   |
LL |     b"\x0Z";  //~ ERROR invalid character in numeric character escape: `Z`
   |          ^ invalid character in numeric character escape

error: non-ASCII character in byte string literal
##[error]  --> /checkout/tests/ui/parser/byte-string-literals.rs:6:7
   |
LL |     b"é";  //~ ERROR non-ASCII character in byte string literal
   |       ^ must be ASCII
   |
help: if you meant to use the unicode code point for 'é', use a \xHH escape
   |
LL -     b"é";  //~ ERROR non-ASCII character in byte string literal
LL +     b"\xE9";  //~ ERROR non-ASCII character in byte string literal
   |

error: non-ASCII character in raw byte string literal
##[error]  --> /checkout/tests/ui/parser/byte-string-literals.rs:7:10
   |
LL |     br##"é"##;  //~ ERROR non-ASCII character in raw byte string literal
   |          ^ must be ASCII

error[E0766]: unterminated double quote byte string
##[error]  --> /checkout/tests/ui/parser/byte-string-literals.rs:8:6
   |
LL |       b"a  //~ ERROR unterminated double quote byte string
   |  ______^
LL | | }
   | |__^

error: aborting due to 6 previous errors
---

5    |                     ^ unknown byte escape
6    |
7    = help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>
+ help: if you meant to write a form feed, use a hex escape
+    |
+ LL - static FOO: u8 = b'\f';
+ LL + static FOO: u8 = b'\x0C';
+    |
8 
9 error: unknown byte escape: `f`
10   --> $DIR/byte-literals.rs:6:8

13    |        ^ unknown byte escape
14    |
15    = help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>
+ help: if you meant to write a form feed, use a hex escape
+    |
+ LL -     b'\f';
+ LL +     b'\x0C';
+    |
16 
17 error: invalid character in numeric character escape: `Z`
18   --> $DIR/byte-literals.rs:7:10

Note: some mismatched output was normalized before being compared
- LL - static FOO: u8 = b'\f';  //~ ERROR unknown byte escape
- LL + static FOO: u8 = b'\\x0C';  //~ ERROR unknown byte escape
- LL -     b'\f';  //~ ERROR unknown byte escape
- LL +     b'\\x0C';  //~ ERROR unknown byte escape
+ help: if you meant to write a form feed, use a hex escape
+    |
+ LL - static FOO: u8 = b'\f';
+ LL + static FOO: u8 = b'\x0C';
+    |
+ help: if you meant to write a form feed, use a hex escape
+    |
+ LL -     b'\f';
+ LL +     b'\x0C';
+    |


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args parser/byte-literals.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/parser/byte-literals.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/parser/byte-literals" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
error: unknown byte escape: `f`
##[error]  --> /checkout/tests/ui/parser/byte-literals.rs:3:21
   |
LL | static FOO: u8 = b'\f';  //~ ERROR unknown byte escape
   |                     ^ unknown byte escape
   |
   = help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>
help: if you meant to write a form feed, use a hex escape
   |
LL - static FOO: u8 = b'\f';  //~ ERROR unknown byte escape
LL + static FOO: u8 = b'\\x0C';  //~ ERROR unknown byte escape
   |

error: unknown byte escape: `f`
##[error]  --> /checkout/tests/ui/parser/byte-literals.rs:6:8
   |
LL |     b'\f';  //~ ERROR unknown byte escape
   |        ^ unknown byte escape
   |
   = help: for more information, visit <https://doc.rust-lang.org/reference/tokens.html#literals>
help: if you meant to write a form feed, use a hex escape
   |
LL -     b'\f';  //~ ERROR unknown byte escape
LL +     b'\\x0C';  //~ ERROR unknown byte escape
   |

error: invalid character in numeric character escape: `Z`
##[error]  --> /checkout/tests/ui/parser/byte-literals.rs:7:10
   |
LL |     b'\x0Z';  //~ ERROR invalid character in numeric character escape: `Z`
   |          ^ invalid character in numeric character escape

error: byte constant must be escaped: `\t`
##[error]  --> /checkout/tests/ui/parser/byte-literals.rs:8:7
   |
LL |     b'    ';  //~ ERROR byte constant must be escaped
   |       ^^^^
   |
help: escape the character
   |
LL |     b'\t';  //~ ERROR byte constant must be escaped
   |       ++

error: byte constant must be escaped: `'`
##[error]  --> /checkout/tests/ui/parser/byte-literals.rs:9:7
   |
LL |     b''';  //~ ERROR byte constant must be escaped
   |       ^
   |
help: escape the character
   |
LL |     b'\'';  //~ ERROR byte constant must be escaped
   |       +

error: non-ASCII character in byte literal
##[error]  --> /checkout/tests/ui/parser/byte-literals.rs:10:7
   |
LL |     b'é';  //~ ERROR non-ASCII character in byte literal
   |       ^ must be ASCII
   |
help: if you meant to use the unicode code point for 'é', use a \xHH escape
   |
LL -     b'é';  //~ ERROR non-ASCII character in byte literal
LL +     b'\xE9';  //~ ERROR non-ASCII character in byte literal
   |

error[E0763]: unterminated byte constant
##[error]  --> /checkout/tests/ui/parser/byte-literals.rs:11:6
   |
LL |     b'a  //~ ERROR unterminated byte constant [E0763]
   |      ^^^^

error: aborting due to 7 previous errors

For more information about this error, try `rustc --explain E0763`.