Fix MemoryFileSystem.makedirs accepting existing files

[Ganesh1729-ui]

Fixes #2266.

Summary

MemoryFileSystem.makedirs(..., exist_ok=True) returned success when the target was an existing file. The target still was not a directory, contrary to the base-method contract and local filesystem behavior. Re-raise FileExistsError when the normalized target is in the memory file store; existing directories remain accepted. This preserves the cache suite's no-metadata-lookup behavior.

The 12 regression cases cover relative, absolute and memory:// paths, both exist_ok values, and the makedirs/mkdirs entry points. Each checks that existing file contents remain intact. A Dev changelog entry describes the fix.

Verification

• Six new cases failed on unchanged original source; all 12 pass with the fix.
• Merged current master at 46c05cb without a force push. The PR diff remains three files, 16 additions and one deletion.
• Full available suite on the merged head: 2,200 passed, 303 skipped, 13 xfailed. Optional service and platform cases account for the skips.
• Following maintainer review, the collision check now uses self.isfile(path), whose implementation normalizes the path and directly checks the in-memory store. The focused memory/cache modules pass 204 tests, 36 skips; the full suite remains 2,200 passed, 303 skipped, 13 xfailed on the reviewed head. Configured hooks pass. Earlier strict Sphinx, source/wheel build and isolated-wheel collision checks passed before the base sync.

AI assistance was used to investigate and prepare the patch. I reviewed the merge resolution and reran the suite and hooks.

[Ganesh1729-ui]

Validation summary for e9241e56: the 12 file-collision cases cover relative, absolute and memory:// paths, both exist_ok values and both directory-creation entry points. Six cases fail on unchanged source; the fixed available suite passes 2,119 tests versus 2,107 on the baseline, with the same 296 skips and 13 xfails.

The normalized store-membership check also preserves the cache suite's no-metadata-lookup assertion. Configured hooks, strict Sphinx, package builds and isolated-wheel checks pass. Optional service/platform skips remain documented. Upstream workflow approval and maintainer review are still pending.

[Ganesh1729-ui]

I merged current master at 8b8bd82 into this branch and resolved the Dev changelog conflict, preserving the new upstream entries and this fix's #2266 entry. The published source change is still the single makedirs condition and its 12 regression cases; the branch is now at 2cade207.

On the merged head, the memory/cache modules pass 187 tests with 36 skips; the full available suite passes 2,141 tests, 296 skips and 13 xfails. All configured hooks pass on the three changed files. No force push or unrelated source adjustment was made.

[martindurant]

Same as self.isfile ? Might be clearer.

[Ganesh1729-ui]

Agreed; MemoryFileSystem.isfile() already normalizes the path and checks self.store directly, so it expresses the intent without adding a metadata lookup. I changed the condition to self.isfile(path) in e17798b. The focused memory/cache modules pass (204 passed, 36 skipped), the full available suite passes (2,194 passed, 298 skipped, 13 xfailed), and the configured hooks pass. Thanks for the clearer spelling.

[Ganesh1729-ui]

The base advanced again after my previous update, so I merged master at 8cf902e into this branch. The only conflict was the Dev changelog block; I kept all new upstream entries and the #2266 entry. The PR still changes only the makedirs condition, its 12 regression cases, and the changelog (three files, 16 additions/one deletion).

On the new db01e63 head, the full available suite passes 2,194 tests with 298 skips and 13 xfails; all configured hooks pass on the three changed files. The branch was pushed normally, with no force push. The PR description now records this head's validation.

[Ganesh1729-ui]

Merged current master (46c05cb) into this branch and resolved the Dev changelog conflict, preserving both new upstream entries and the memory makedirs entry. Current head is e123947; the PR diff remains three files, 16 additions and one deletion. The reviewed self.isfile(path) check remains intact.

Validation on the merged source: memory/cache modules 204 passed / 36 skipped; full available suite 2,200 passed / 303 skipped / 13 xfailed; all configured hooks pass. The PR description now reflects this head and these results.