Format-preserving pretty-printing with replacing expression nodes doesn't work #1115
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maks-rafalko
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maks-rafalko
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maks-rafalko
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Oct 21, 2025
Format-preserving pretty printing is hard :| After a week of evenings of debugging, here we go. https://github.com/nikic/PHP-Parser/blob/master/doc/component/Pretty_printing.markdown#formatting-preserving-pretty-printing Why is this needed? - To correctly highlight mutated code in PhpStorm Plugin (requested here: #2425 (comment)) - To have original code in code diffs for each Mutant. Previously, the code was reformatted by PrettyPrinter from `php-parser` Instead of 1000 words, examples: Before: ```diff @@ @@ } public function logVerbosityDeprecationNotice(string $valueToUse): void { - $this->logger->notice('Numeric versions of log-verbosity have been deprecated, please use, ' . $valueToUse . ' to keep the same result', ['block' => true]); + $this->logger->notice('Numeric versions of log-verbosity have been deprecated, please use, ' . $valueToUse . ' to keep the same result', []); } public function logUnknownVerbosityOption(string $default): void { ``` After: ```diff @@ @@ { $this->logger->notice( 'Numeric versions of log-verbosity have been deprecated, please use, ' . $valueToUse . ' to keep the same result', - ['block' => true], + [], ); } ``` As you can see, previously Infection **modified** the source code formatting, then created a Mutant, and then compared modified original code with mutant. Now, original code is compared with a mutant as is - we ONLY change the mutated node. No more reformatting. This gives us much more readable and clear diffs. Long multiline arrays are no longer changed to lengthy one-liners. ---- During implementation, I found several bugs in `php-parser`: - nikic/PHP-Parser#1115 - nikic/PHP-Parser#1116 - nikic/PHP-Parser#1117 - nikic/PHP-Parser#1119 These are not blockers, but interesting to see the answers from Nikita. I have a feeling that either these are bugs or we don't use nodes replacements correctly (probably we should do them in-place) - let's see. ---- - [x] check how HTML report works after these changes
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Hello,
at Infection, we do a lot of nodes replacements during the Mutation Testing process.
For example (see tests in this PR), we replace
+with-.So for the following code:
I would expect the following result:
However, as PHPUnit test failure says, we get:
So basically formatting disappears and we get
Notes: the same code saves formatting when we replace number with another one, not the
+expression. It is tested here:PHP-Parser/test/code/formatPreservation/basic.test
Lines 1 to 19 in 0da2d66
I'm working on a new update for Infection to produce format-preserved diffs for developers, and among 5000+ mutations found more interesting cases where format isn't preserved, but let's keep it simple with this one for now. If this one is a bug, I can create separate issues for other cases.