ensure-directories-exist

(ensure-directories-exist pathspec)

Creates the directory component of pathspec, including every missing parent, and returns pathspec. The directory component is everything up to and including the last /, so "logs/app.log" creates logs/ and leaves the file alone; a namestring that already ends in / is the directory; a namestring with no / names a file in the working directory and creates nothing. An existing directory is not an error.

Lite: Common Lisp returns (values pathspec created) and this returns the pathspec only — a second value would not survive the function boundary on the compiled backends, so promising one would be misleading.

Both WASM backends signal at call time. No WASI directory-creation call is imported there, and unlike file-write-date this operation has no "cannot be determined" answer in its contract: either the directory exists afterwards or it does not, so answering anything but an error would be a lie.

(ensure-directories-exist "logs/2026/app.log")
(with-open-file (out "logs/2026/app.log" :direction :output)
  (write-line "started" out))