w3id.org

Appearance

tree/no-case-collision ​

Severity: error · Status: enforced · Applies to: ids/**

What ​

An identifier directory name must not differ from an existing one only by letter case.

Why ​

macOS and Windows use case-insensitive filesystems by default. If ids/Foo/ and ids/foo/ both exist, the repository cannot be checked out on those platforms — Git either merges them into one directory or fails outright. That breaks the working copy for a large share of contributors and maintainers, and the failure is confusing because it has nothing to do with the file they were editing.

Linux, where the production server runs, is case-sensitive, so the collision is invisible until somebody clones the repository on a laptop.

This has happened here before. The global ids/.htaccess carries rules that exist for no reason other than papering over past collisions, and identifiers have had to be renamed after the fact.

Lowercase names are preferred beyond just avoiding collisions — they remove the question of which capitalisation a user should type — but that preference is not mechanically checked.

Wrong ​

Given that ids/my-project/ already exists:

ids/MY-PROJECT/       ← collides
ids/My-Project/       ← collides
ids/my-project/
ids/my-project-extended/

Lowercase letters, digits, and hyphens.

How to fix ​

Before you choose a name, check case-insensitively for existing variants:

sh
ls ids/ | grep -i '^my-project$'

If you need to rename a directory you already committed, do it in two steps so Git records the change on case-insensitive filesystems too:

sh
git mv ids/MyProject ids/myproject-tmp
git mv ids/myproject-tmp ids/my-project

If you need both capitalisations to resolve — an existing IRI used a capitalised form and you are standardising on lowercase — do not create two directories. Keep one, and ask a maintainer about adding a redirect rule for the other form. Those rules live in the global ids/.htaccess, which is not a file contributors edit themselves — see tree/only-own-identifier.

How to check ​

Run w3id-check with --rule tree/no-case-collision to check this rule on its own; without it the tool runs every rule, as the pull request checks do.

sh
node tools/check/bin/w3id-check.js --rule tree/no-case-collision ids/my-project

The check needs the whole tree to see a collision, so it works from a full checkout even when you scope it to one directory.

Testing your changes covers installing the tool, and what else is worth checking by hand.

See also ​