fatal error with absolute -build-dir

[vicuna]

Original bug ID: 5503
Reporter: Hendrik Tews
Assigned to: @xclerc
Status: closed (set by @xavierleroy on 2015-12-11T18:19:49Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 3.12.1
Fixed in version: 3.13.0+dev
Category: -for ocamlbuild use https://github.com/ocaml/ocamlbuild/issues
Has duplicate: #4502
Monitored by: mehdi @glondu @xclerc @jberdine jm

Bug description

ocamlbuild uses wrong filename concatenation when it tries to open the _digest file. It therefore dies with a Sys_error when given an absolute build dir.

Steps to reproduce

touch t.ml
ocamlbuild -build-dir /tmp/x t.byte

this dies with

Fatal error: exception Sys_error("/tmp//tmp/x/_digests: No such file or directory")

because it does

open("/tmp//tmp/x/_digests", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = -1 ENOENT (No such file or directory)

Additional information

The bug is also present in 3.13.0+dev11 (2012-01-26)

File attachments

• pr-5503.diff

[vicuna]

Comment author: @xclerc

Tentative fix in trunk by commit 12154.
Could you confirm it fixes the issue on your machine?

[vicuna]

Comment author: jm

the current fix breaks builds not giving -build-dir;
as ocamlbuild tries to write in _build/_build/:

• ocamlfind ocamlc -where > _build/ocamlc.where
  /bin/sh: cannot create _build/ocamlc.where: Directory nonexistent
  Command exited with code 2.
  Compilation unsuccessful after building 1 target (0 cached) in 00:00:00.
  Fatal error: exception Sys_error("_build/_digests: No such file or directory")

[vicuna]

Comment author: @avsm

I fixed it with the attached one-liner in pr-5503.diff, which seems to work both with and without a build-dir specified.

[vicuna]

Comment author: @damiendoligez

Fixed in trunk (commit 12191).

Hopefully, this fix will work with all combinations (without -build, with -build relative, with -build absolute).

The fix is actually from Xavier, I'm the committer for technical reasons.