Fix: change display impl to match as str

[Teolhyn]

Fixes issue #1149.

Bug description from the original issue:

When you do pair.to_string() and pair.as_str().to_string() you get different strings - the former gives the pair name and it's range, the latter the actual span content . This is pretty confusing as foo.as_str().to_string() should generally be equivalent to foo.to_string(). Users the library will think it is and it will lead to bugs. I personally did so and it wasn't pleasant to realize what was the cause

What was done

Display implementation for Pair was changed as this is where to_stringcomes from. Rather than giving pair name and it's range it now simply returns the span content using as_str, which quarantees that as_str().to_string() and to_string() will give the same output for Pair, even if for some reason as_str would be changed in future. I also added a simple unit test for this.

Considerations

This changes how displaying of Pairs work. However, there was already a Debug implementation that would give the whole Pair struct.

This is my first ever (code) contribution to OSS, so any feedback would be appreciated.

Summary by CodeRabbit

• Refactor

  • Rendering of parsed items and collections now defaults to their plain string content; an alternate (pretty-printed) format shows a nested, structured view when requested.

• Tests

  • Added and updated tests to ensure plain-string rendering and the alternate pretty-printed formatting behave as expected.

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[coderabbitai]

📝 Walkthrough

Walkthrough

Display implementations for Pair and Pairs were changed to support alternate (“pretty”) formatting: normal formatting renders the pair(s) as their source string(s), while alternate formatting emits a nested, pretty-printed representation including rule, start/end, and inner pairs. Tests were added/updated accordingly.

Changes

Cohort / File(s)	Summary
Pair Display & tests pest/src/iterators/pair.rs	Changed Display for Pair to render self.as_str() for normal formatting and a nested pretty-printed structure when f.alternate() is true; updated imports and added pair_to_string_matches_as_str and alternate_format tests.
Pairs Display & tests pest/src/iterators/pairs.rs	Changed Display for Pairs to join inner Pair renderings, using normal formatting for non-alternate and pretty/debug-style ({pair:#}) for alternate; updated pairs_display test expectation to match new non-alternate output and preserved alternate formatting expectations.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐇 I nibble tokens, tidy and neat,
I fold inner hops into a neat beat.
When asked for pretty, I stretch and show,
Else I whisper the string that I know. 🥕

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Fix: change display impl to match as str' directly describes the main change: modifying the Display implementation for Pair to match the output of as_str().

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✨ Finishing touches

• 📝 Generate docstrings

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[tomtau]

maybe the old formatting can be preserved with the "alternate" flag on the formatter (or the other way round)?
so one can have both with format!("{pair}") and format!("{pair:#}") ?

[tomtau]

if it's removed here, the tests should import it: https://github.com/pest-parser/pest/actions/runs/21472450223/job/61858601867?pr=1151#step:4:240

[Teolhyn]

It seems like format is used in cfg("pretty-print") so I added the import under feature flag.

[Teolhyn]

maybe the old formatting can be preserved with the "alternate" flag on the formatter (or the other way round)? so one can have both with format!("{pair}") and format!("{pair:#}") ?

I added this now so that format!("{pair}") uses the new formatting that matches as_str and format!("{pair:#}") matches the old formatting. I updated tests for pair and pairs. Let me know what you think.