The implicit "any unprefixed line is an ignore pattern" rule is the last source of subtle parser surprises — it's the reason why a single leading space silently changes a +-keep into a literal ignore pattern, and it makes typo'd comments slip through as ignores. Mark these lines as :legacy-ignore in the classifier, record them in a new prefixless-ignore slot on the dirconfig struct, and emit a one-time warning per project listing the offending entries. The behavior is unchanged — the lines still go into the ignore list — but users now get a nudge to write them as -entry. The warning can be silenced via projectile-warn-on-prefixless-dirconfig-lines.
The old parser walked a temp buffer with point and pcase'd on char-after, mixing IO, prefix dispatch, and bucket bookkeeping into one function. Pull the dispatch out into projectile--dirconfig-classify-line, which takes a string and returns a (BUCKET . VALUE) tag. The pure function is unit-testable without buffer plumbing, the IO wrapper shrinks to a one-shot read + dispatch, and the awkward (pcase ((pred (lambda ...)) ...)) for the comment-prefix check becomes a straightforward cond. No behavior change.
Replace the positional (KEEP IGNORE ENSURE) triple with a cl-defstruct. Every internal call site used car/cadr/caddr to pull out a slot, which is unreadable and error-prone — slot accessors make the intent explicit and let cl-defstruct grow a fourth field later without touching every consumer. Existing callers that compared against the raw triple (a couple of internal helper tests) are updated to construct the struct with make-projectile-dirconfig.
Improvements to .projectile (dirconfig) parsing and ergonomics
The parser silently turns every keep entry into a directory via file-name-as-directory, which means a user-typed +*.json or +/foo.txt becomes "*.json/" or "foo.txt/" and quietly never matches anything. Spot the obvious misuses (anything containing *, ?, or [) at parse time and emit a warning so the user can correct the file or move the pattern to an ignore/ensure rule.
The existing parser tests stub insert-file-contents; nothing exercises the full IO path. Add three sandbox-based tests: a mixed +/-/!/no-prefix file, a non-ASCII round-trip, and a file with no trailing newline. These guard against IO-layer regressions that the stubbed tests can't see.
Under alien indexing the dirconfig file is silently ignored, which is the most common confusion in the issue tracker (#1322, #1075, #1534, #1941). Show a one-shot display-warning the first time we index a project where alien mode meets a non-empty .projectile. The new projectile-warn-when-dirconfig-is-ignored option lets users who already understand the trade-off silence the warning.
The parser docstring only described + and - prefixes even though the function returns a 3-tuple including the ! ensure bucket. Fill that in, and pull the path-vs-glob distinction out of the prose in projects.adoc into a subsection of its own — that ambiguity is at the root of recurring confusion (#740, #1109, #680, #1941).
The mtime-keyed cache around projectile-parse-dirconfig-file had no direct coverage. Cover the four invariants that matter: a cache hit on repeat calls, a re-parse when mtime advances, no caching of a nil result for a missing file, and entry removal via projectile-invalidate-cache (the path that previously crashed in #1854).
A user accidentally typing " -path/" or " # comment" in .projectile would have the line silently routed to the ignore bucket with the prefix character left intact, because the parser dispatched on the first character of the line without trimming. Skip leading spaces and tabs before the pcase so the +/-/! and comment-prefix markers are matched regardless of indentation. Reported in #1508.