[rajanpanth]

Description

What is the purpose of this pull request?

This pull request:

• inserts zero padding after a + or sign and after a 0x/0X prefix in string/base/format-interpolate (and thus string/format). Previously, only a leading - was moved in front of the zeros, so the zeros landed in front of the sign or the prefix.
• always applies the zero padding requested by an integer precision on the left. Previously, the - flag (left-justify) also flipped the precision padding to the right, which changed the value: format( '%-.5d', 10 ) returned '10000'. In C, - only affects how the result is padded to the field width.

Format	Value	Before	After (= C printf)
%+05d	42	00+42	+0042
% 05d	42	00 42	0042
%#08x	255	00000xff	0x0000ff
%+08.3f	3.14159	00+3.142	+003.142
%-.5d	10	10000	00010
%-8.3d	-7	-700	-007

Related Issues

Does this pull request have any related issues?

None.

Questions

Any questions for reviewers of this pull request?

No.

Other

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

• One existing unit test in test/test.format_integer.js asserted the old behavior ({ 'precision': 5, 'padRight': true } with 10 returned '10000'). I updated its expected value to '00010', which is what C's printf( "%-.5d", 10 ) produces. All other existing tests pass unchanged.
• New tests cover each row of the table above, plus zeroPad directly with sign and hexadecimal prefixes. The new test.js tests fail on develop (8 assertions), as do the new test.zero_pad.js tests (5 assertions).
• I checked the expected values against Python's % operator, which matches C for these cases.
• This is independent of fix: remove trailing zeros and handle zero and zero precision for %g in string/base/format-interpolate #16538 (%g), which touches format_double.js only.
• I ran the tests for string/base/format-interpolate and string/format directly with Node.js and tape on Windows (as make was not available in my environment); I did not run the full repository lint pipeline locally.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

AI Assistance

When authoring the changes proposed in this PR, did you use any kind of AI assistance?

• Yes
• No

If you answered "yes" above, how did you use AI assistance?

• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
• Research and understanding

Disclosure

If you answered "yes" to using AI assistance, please provide a short disclosure indicating how you used AI assistance. This helps reviewers determine how much scrutiny to apply when reviewing your contribution. Example disclosures: "This PR was written primarily by Claude Code." or "I consulted ChatGPT to understand the codebase, but the proposed changes were fully authored manually by myself.".

This PR was written with the help of Claude Code, which found the issue, drafted the implementation change and tests, and checked the results against C's printf semantics. I reviewed the changes and the test results before submitting.

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@stdlib-js/reviewers

🤖 Generated with Claude Code

[kgryte]

@Planeshifter Mind taking a look at these changes since you were the one which originally added this functionality?