GitHub Copilot `file_search` glob with `\**\` (backslash double-star) produces partial or no results where `/**/` succeeds

[garretwilson]

Summary

In GitHub Copilot's file_search tool, using backslashes around the ** glob segment (root\**\file.ext) produces fewer results or no results compared to the forward-slash equivalent (root/**/file.ext). Non-glob path segments handle both slash directions interchangeably, so the inconsistency is specific to the ** glob operator.

This is the second of three related bugs in Copilot's search tools affecting multi-root workspaces on Windows. The principal issue is tracked in #293428.

Environment

• OS: Windows 11
• VS Code: 1.109
• Workspace: Multi-root (3 roots)

Reproduction

Setup

Create a multi-root workspace with one root:

C:\projects\alpha\       ← workspace root "alpha"
    readme.md
    src/
        util/
            Helper.java

Steps

1. Use file_search with query: "alpha/**/Helper.java".
2. Use file_search with query: "alpha\**\Helper.java".
3. Use file_search with query: "alpha/**/readme.md".
4. Use file_search with query: "alpha\**\readme.md".

Expected

Steps 1–4 all find the respective files.

Actual

• Step 1 (/**/): ✅ Finds Helper.java.
• Step 2 (\**\): ❌ No results, or partial results depending on root.
• Step 3 (/**/): ✅ Finds readme.md.
• Step 4 (\**\): ⚠️ May return fewer results. In testing, \**\ appears to require at least one path segment between the prefix and the filename, missing files where ** should match zero segments.

The Discrepancy

Pattern	/ separators	\ separators
alpha/**/file.ext (root-prefixed glob)	✅ All results	❌ or ⚠️ Partial/no results
alpha/src/file.ext (root-prefixed explicit)	✅	✅
**/file.ext (recursive glob)	✅	✅
alpha/src/*.ext (single-star glob)	✅	✅

The issue is isolated to ** when surrounded by backslashes. Single-star globs (*), explicit paths, and non-glob backslash segments all work correctly with either separator. The ** glob with forward slashes also works correctly. Only the combination of ** with \ is affected.

Observed Variation Across Roots

In a multi-root workspace with three roots, the \**\ pattern was tested with each root name as prefix:

Pattern	/**/	\**\
Root A (name appears as internal directory in its own tree)	✅	✅ (partial — fewer results)
Root B (name does not appear as internal directory)	✅	❌ No results
Root C (name does not appear as internal directory)	✅	❌ No results

Root A's partial success with \**\ may be due to the same coincidental-directory-name matching described in #293428. The /**/ form works consistently for all roots.

Impact on LLMs

On Windows, LLMs sometimes produce backslash-separated paths. When combined with ** glob patterns, this causes file_search to silently return fewer or no results. Since non-glob backslash paths work fine, the failure appears intermittent from the LLM's perspective — backslash paths work in some calls but not others, depending solely on whether ** is present.

Root Cause Hypothesis

The glob engine used by file_search likely normalizes / and \ for literal path segments but does not normalize the separators adjacent to **. The ** operator may be recognized only when delimited by / (i.e., /**/), causing \**\ to be interpreted as a literal segment match or a malformed glob rather than a recursive wildcard.

Recommendation

The file_search glob engine should normalize \**\ to /**/ before evaluation, or treat ** as a recursive wildcard regardless of surrounding separator characters.

Related Issues

• GitHub Copilot grep_search includePattern silently fails with workspace root folder name prefix in multi-root workspaces (severe) #293428 — grep_search includePattern silently fails with workspace root folder name prefix in multi-root workspaces (principal issue).
• Malformed absolute paths in read_file and list_dir trigger "Allow reading external files?" prompt, then fail on GitHub Copilot #293204 — Malformed absolute paths trigger "Allow reading external files?" prompt, then fail. Affects read_file and list_dir.

[garretwilson]

VS Code Search Tool Path Resolution — Comprehensive Test Matrix

Legend

• ✅ = works correctly
• ❌ = silent failure (no results or nonexistent file error)
• 🔶 = triggers spurious "external file/directory" security prompt, then fails
• ⚠️ = partial results (fewer matches than expected)
• — = not applicable (tool doesn't accept this format)

Bug Key

• A = GitHub Copilot grep_search includePattern silently fails with workspace root folder name prefix in multi-root workspaces (severe) #293428 — grep_search rejects root-name prefix
• B = GitHub Copilot file_search glob with \**\ (backslash double-star) produces partial or no results where /**/ succeeds #293430 — file_search \**\ glob failure
• C = Malformed absolute paths in read_file and list_dir trigger "Allow reading external files?" prompt, then fail on GitHub Copilot #293204 — malformed absolute paths trigger external-file prompt

Path Formats Tested

#	Format	Example
1	Root-relative, /	src/main/App.java
2	Root-relative, \	src\main\App.java
3	Root-relative, mixed	src\main/App.java
4	Recursive glob, /	**/App.java
5	Recursive glob, \	**\App.java
6	Root-prefixed, explicit, /	alpha/src/main/App.java
7	Root-prefixed, explicit, \	alpha\src\main\App.java
8	Root-prefixed, /**/ glob	alpha/**/App.java
9	Root-prefixed, \**\ glob	alpha\**\App.java
10	Windows absolute, \	C:\projects\alpha\src\App.java
11	Windows absolute, /	C:/projects/alpha/src/App.java
12	Git Bash absolute	/c/projects/alpha/src/App.java
13	Leading \, no colon	\c\projects\alpha\src\App.java

Results

#	Path Format	file_search	grep_search	read_file	list_dir
1	root-relative /	✅	✅	—	—
2	root-relative \	✅	✅	—	—
3	root-relative mixed	✅	✅	—	—
4	**/file /	✅	✅	—	—
5	**\file \	✅	✅	—	—
6	root-prefixed /	✅	❌ A	—	—
7	root-prefixed \	✅	❌ A	—	—
8	root /**/ glob	✅	❌ A	—	—
9	root \**\ glob	⚠️ B	❌ A	—	—
10	C:\ absolute	—	❌	✅	✅
11	C:/ absolute	—	❌	✅	✅
12	/c/ Git Bash	—	❌	🔶 C	🔶 C
13	\c\ no colon	—	❌	🔶 C	🔶 C

Reading the Table

• Bug A (rows 6–9, grep_search column): root-name prefix silently rejected.
• Bug B (row 9, file_search column): \**\ glob produces partial/no results.
• Bug C (rows 12–13, read_file/list_dir columns): malformed absolute paths prompt then fail.
• Rows 1–5: all tools agree — these are the safe patterns.
• Rows 10–11: correct absolute paths work for read_file/list_dir; file_search and grep_search don't accept absolute paths (by design, not a bug).

[roblourens]

The basic setup doesn't make sense to me, doesn't it contradict #293428? We don't resolve the alpha in that glob, so if the LLM does what you say, none of those cases work for me. It doesn't really matter though, once the general fix microsoft/vscode-copilot-chat#4287 is in, we should just see whether that fixes whatever you were seeing. You wrote 1000 lines here where just seeing one log showing the actual tool args from the LLM in context would have been much more clear, but I know you don't like to share logs.

[garretwilson]

… none of those cases work for me.

I appreciate that someone is looking into this, and if you can't reproduce it I will certainly try to help you. Just be clear though: you are saying you performed the setup in the description on a Windows system? (I don't know if the OS is related; I just want to be clear on what you did in attempting to reproduce this.)

Note however that of these three bugs, #293428 is the most critical, As it mentions:

This is the single largest source of LLM search failures in multi-root workspaces.

[roblourens]

Yeah, I tried on Windows. I agree that issue is the primary problem, my PR fixes that. If you haven't seen, we are starting to do stable vscode releases more often. I will merge the PR this week, and it will be in stable starting next week. I need to do more testing of my PR on Windows first.

[garretwilson]

I agree that issue is the primary problem, my PR fixes that.

@roblourens that is amazing news! Thank you!

If you haven't seen, we are starting to do stable vscode releases more often.

I hadn't seen. Thanks for the heads-up!