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String Debug implementation prints escaped single quotes #83046

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marcianx opened this issue Mar 12, 2021 · 2 comments · Fixed by #83079
Closed

String Debug implementation prints escaped single quotes #83046

marcianx opened this issue Mar 12, 2021 · 2 comments · Fixed by #83079
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C-bug Category: This is a bug.

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@marcianx
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This is very minor.

println!("{:?}", "'");

(playground)

Expected output: "'"
Actual output: "\'"

Perhaps this was intentional, but I'm not sure why it would be. The closest issue I saw was #3752 which is ancient and was more obviously a bug since escapes were appearing in Display output and not just Debug.

This reproduces in the latest stable (1.50.0) and nightly (1.52.0-nightly) builds.
@marcianx marcianx added the C-bug Category: This is a bug. label Mar 12, 2021
@osa1
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osa1 commented Mar 13, 2021

This is because the same format string method of char (escape_debug_ext) is used for Debug implementation of both str and char (and a few other internal types), so it needs to escake ' otherwise in char context it would generate incorrect Debug string. Adding a is_char argument to this method solves the issue. I tested this and it passes ui tests.

I checked the language spec https://doc.rust-lang.org/stable/reference/tokens.html#string-literals I don't think "\'" is a valid string, right? Am I missing anything?

@osa1 osa1 mentioned this issue Mar 13, 2021
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@marcianx
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Oh, wow. Until you mentioned it, I didn't even notice that this also affects char's Debug output as well so that println!("{:?}", '"'); prints '\"'. Thanks for fixing them both!

bors added a commit to rust-lang-ci/rust that referenced this issue Mar 26, 2021
@bors
Auto merge of rust-lang#83079 - osa1:issue83046, r=m-ou-se
4137088 
Update char::escape_debug_ext to handle different escapes in strings and chars

Fixes rust-lang#83046

The program

    fn main() {
        println!("{:?}", '"');
        println!("{:?}", "'");
    }

would previously print

    '\"'
    "\'"

With this patch it now prints:

    '"'
    "'"
@bors bors closed this as completed in 819247f Mar 26, 2021
@dsferruzza dsferruzza mentioned this issue Apr 21, 2021
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@tmpolaczyk tmpolaczyk mentioned this issue Jun 24, 2021
Closed
@keith-hall keith-hall mentioned this issue May 21, 2022
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@tamird tamird mentioned this issue Aug 7, 2023
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Update char::escape_debug_ext to handle different escapes in strings and chars
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@marcianx @osa1