fix(util): quote top-level strings in util.format %o/%O (Node parity)

[proggeramlug]

Problem

util.format("%o", "hello") and console.log("%o", str) printed the string unquoted (hello), but Node renders %o/%O arguments through util.inspect, which quotes strings: 'hello'.

# node v26.3.0           # perry (before)
util.format("%o","hi") → 'hi'        util.format("%o","hi") → hi
util.format("%O","hi") → 'hi'        util.format("%O","hi") → hi

Root cause

The %o/%O arms called format_jsvalue(val, 0), which mirrors the bare console.log(str) behavior of leaving a top-level string unquoted. But %o/%O should inspect the value, and util.inspect quotes strings at every depth (nested strings already came out right — %o of {a:"x"} → { a: 'x' }). js_util_inspect already special-cases top-level strings (format!("'{}'", escape_string(&s))); the %o/%O path just didn't.

Fix

Route the %o/%O argument through a new inspect_format_arg helper that mirrors js_util_inspect's top-level handling: a primitive string becomes '<escaped>', everything else goes through format_jsvalue.

Verification (vs Node v26.3.0)

%o "hello" → 'hello'      %O "hello" → 'hello'     %o 42 → 42
%o {a:"x"} → { a: 'x' }   %o null → null           %o true → true
%s "hello" → hello   (unchanged — %s coerces, no quotes)

Existing perry-runtime formatting + inspect unit tests pass (12). Found via a util.format/util.inspect differential sweep against Node; relates to the console/util-formatting parity gap noted in CLAUDE.md and the parity roadmap (#4315).

Out of scope: Node's %o also sets showHidden, so an array prints [ 1, 'two', [length]: 2 ]; matching that internal-slot rendering is a separate showHidden-array feature, left as-is.

No version bump / changelog per maintainer instruction.

Summary by CodeRabbit

• Bug Fixes
  • Improved formatting for %o and %O so string arguments are now rendered with quotes and proper escaping, matching util.inspect-style output.
  • Non-string values keep the same formatting behavior as before to ensure consistency across all other types.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 5df8dcc8-7899-46be-9cc0-7db336dbb254

📥 Commits

Reviewing files that changed from the base of the PR and between 61f62a8 and 0d172c4.

📒 Files selected for processing (1)

• crates/perry-runtime/src/builtins/formatting/util_format.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• crates/perry-runtime/src/builtins/formatting/util_format.rs

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📝 Walkthrough

Walkthrough

A new internal helper inspect_format_arg is added to util_format.rs. It quotes and escapes top-level string values (matching util.inspect semantics) and delegates non-strings to format_jsvalue(val, 0). The %o and %O placeholder branches in js_util_format are updated to call this helper instead of calling format_jsvalue directly.

Changes

util.inspect string quoting for %o/%O

Layer / File(s)	Summary
inspect_format_arg helper and %o/%O wiring crates/perry-runtime/src/builtins/formatting/util_format.rs	Adds inspect_format_arg (lines 115–130) to quote and escape top-level strings, then wires it into the %o and %O branches (lines 343–348) of js_util_format replacing the direct format_jsvalue(val, 0) calls.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~5 minutes

Poem

🐇 A string walked in wearing %o's disguise,
And found itself quoted — what a surprise!
With backslashes neatly placed just so,
inspect_format_arg puts on a show.
The rabbit hops on, the output shines bright! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: fixing util.format to quote top-level strings in %o/%O format specifiers to match Node.js behavior.
Description check	✅ Passed	The description is comprehensive with problem statement, root cause analysis, fix explanation, and verification against Node v26.3.0. All required template sections are addressed with concrete details.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

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• Create stacked PR
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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/util-format-o-string-quote

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