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improve custom message format in assert_eq macro #94016

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improve custom message format in assert_eq macro #94016

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426c85b
optimize panic message format in assert_eq macro
MakitaToki Feb 15, 2022
fa00953
align colons in assert_failed_inner
MakitaToki Feb 16, 2022
e575215
change message format in 'assert_failed_inner' function
MakitaToki Feb 19, 2022
108f87e
delete trailing whitespaces
Feb 19, 2022
1ef6ba5
stringify original tokens
MakitaToki Feb 28, 2022
a1aed4a
resolve merged conflict
MakitaToki Feb 28, 2022
099818b
accept local changes
MakitaToki Feb 28, 2022
024f125
stringify original tokens in related macros
MakitaToki Feb 28, 2022
657a52b
Merge branch 'issue-94005-fix' of github.com:Mizobrook-kan/rust into …
MakitaToki Feb 28, 2022
ded501c
clean up output format
MakitaToki Mar 6, 2022
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3 changes: 2 additions & 1 deletion library/core/src/panicking.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -219,7 +219,8 @@ fn assert_failed_inner(
Some(args) => panic!(
r#"assertion failed: `(left {} right)`
left: `{:?}`,
right: `{:?}`: {}"#,
right: `{:?}`,
context: `{:?}`"#,
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It looks like the intent here was to align left: and right: with each other along the : - probably we want to do the same with context: if we do this?

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updated as suggested

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Do I continue to submit more commits according to yaahc's suggestions, or close this PR?

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Go ahead and update the format as suggested.

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@MakitaToki MakitaToki Feb 19, 2022 •
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Change panicking.rs in core package and that one in std remains the same as the latter makes more failed tests.
The current output format is like this:

thread 'main' panicked at 'assertion failed: `(upper_bounds == target)`
   Error: `1 + 1 definitely should be 3`,
   upper_bounds: `2`,
   target: `3`', /home/kougami/temp/rust/src/test/ui/macros/assert-eq-macro-msg.rs:8:5

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@MakitaToki MakitaToki Feb 25, 2022 •
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This is my mistake. I definitely misunderstood your original comment. Do you want to stringify parameter names? @yaahc
Is it like this?

        Some(args) => panic!(
            r#"assertion failed: `(left {} right)`
  left: {},
 right: {}: {}"#,
            stringify!(op), stringify!(left), stringify!((right), stringify!(args)
        ),

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not exactly, stringify! stringifies exactly whatever you pass into it, so calling stringify!(op) will just give you "op". Instead you'd need to call stringify! from inside of the assert_eq! macro_rules definition where you still have access to the original tokens, then you'd have to add arguments to assert_failed and assert_failed_inner to pass the strings all the way to the inner function that formats them, so it would look something like this:

// in `library/core/src/macros/mod.rs`
macro_rules! assert_eq {
    ($left:expr, $right:expr $(,)?) => ({
        match (&$left, &$right) {
            (left_val, right_val) => {
                if !(*left_val == *right_val) {
                    let kind = $crate::panicking::AssertKind::Eq;
                    let left_name = stringify!($left);
                    let right_name = stringify!($right);
                    // The reborrows below are intentional. Without them, the stack slot for the
                    // borrow is initialized even before the values are compared, leading to a
                    // noticeable slow down.
                    $crate::panicking::assert_failed(kind, &*left_val, &*right_val, left_name, right_name, $crate::option::Option::None);
                }
            }
        }
    });
   // the rest of the assert_eq definition ...
}

// in `library/core/src/panicking` assert_failed_inner
fn assert_failed_inner(
    kind: AssertKind,
    left: &dyn fmt::Debug,
    right: &dyn fmt::Debug,
    left_name: &'static str,
    right_name: &'static str,
    args: Option<fmt::Arguments<'_>>,
) -> ! {
    let op = match kind {
        AssertKind::Eq => "==",
        AssertKind::Ne => "!=",
        AssertKind::Match => "matches",
    };

    match args {
        Some(args) => panic!(
            r#"assertion failed: `({left_name} {} {right_name})`
  {left_name}: `{:?}`,
 {right_name}: `{:?}`: {}"#,
            op, left, right, args
        ),
       // ....
}

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I tried my best to find some code snippets that needs to be updated. Is there anything else I'm missing?

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no, this looks perfect! We just need to get the exact output sorted and update the test UI files so everything passes. Right now looking at the failed test in CI the output looks like this:

 thread 'main' panicked at 'assertion failed: `(1 + 1 == 5)`
  1 + 1: `2`,
 5: `5`', /checkout/src/test/ui/test-attrs/test-panic-abort.rs:34:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

So we probably want to clean this up a bit, and we may want to rethink how many times we repeat the stringified version of the expression. Here's my suggestion for what we should aim for:

thread 'main' panicked at 'assertion failed: `(1 + 1 == 5)`
  left: `2`,
 right: `5`'
    at: /checkout/src/test/ui/test-attrs/test-panic-abort.rs:34:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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updated my commit

op, left, right, args
),
None => panic!(
Expand Down