Preserve replace string when match has no cased characters

[Lakshya Pandey (pandeylakshya207-max)]

Fixes #192168

Problem

With "Preserve Case" enabled, replacing a match that contains no cased
characters uppercases the replace string. Searching for () and replacing
with fontSize: 20 produces FONTSIZE: 20.

buildReplaceStringWithCasePreserved decides the match is uppercase using
matches[0].toUpperCase() === matches[0]. Punctuation and digits are
unchanged by toUpperCase(), so that check passes for matches that have no
case at all, and the replace string is uppercased. The same applies to
matches like 123.

Fix

Return the replace pattern unchanged when the match contains no cased
characters, detected with toLowerCase() === toUpperCase(). This is true
only for strings with no cased characters, so it also covers whitespace and
scripts without case.

The check runs before the hyphen/underscore handling, which recurses into
this function per segment, so caseless segments are left alone too.

Testing

• Added cases to both buildReplaceStringWithCasePreserved test and
  preserve case in replacePattern.test.ts. All 16 tests in the suite
  pass; the 22 existing assertions are unaffected since every one of them
  has a match containing letters.
• npm run eslint is clean.
• Verified manually in Code - OSS on Windows 11: searching () and
  replacing with fontSize: 20 with Preserve Case on now yields
  fontSize: 20. Checked that abc→Def still gives def, ABC→Def
  gives DEF, and Abc→Def gives Def.

[Lakshya Pandey (pandeylakshya207-max)]

@microsoft-github-policy-service agree

[Copilot]

🟡 Changes recommended

The segmented-match assertions do not exercise the recursive behavior they intend to cover.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Fixes preserve-case replacement for matches containing no cased characters.

Changes:

• Returns replacement patterns unchanged for caseless matches.
• Adds regression coverage for punctuation and numeric matches.

File summaries

File	Description
src/vs/base/common/search.ts	Detects caseless matches before transforming replacement case.
src/vs/editor/contrib/find/test/browser/replacePattern.test.ts	Adds caseless-match tests.

Review details

Suppressed comments (1)

src/vs/editor/contrib/find/test/browser/replacePattern.test.ts:262

• This wrapper assertion also ignores the second array item because only matches[0] drives case preservation, so it duplicates the punctuation case rather than covering separator recursion. Use a mixed cased/caseless segmented match instead.

		assertReplace(['(', ')'], 'fontSize: 20', 'fontSize: 20');

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Balanced

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[Lakshya Pandey (pandeylakshya207-max)]

Thanks — both good catches, addressed in fb2a976.

The ['(', ')'] case only ever read matches[0], so it was a duplicate of the punctuation test rather than covering separator recursion. Replaced it with ['ABC-123'] → 'Def-someValue' → 'DEF-someValue', which exercises the hyphen path with one cased and one caseless segment.

Comment condensed to a single line. All 16 tests in the suite still pass locally.