Question

I’m trying to write a makefile snippet to compile .el files to .elc files. I have the following snippet:

.el.elc:
        $(EMACS) -q -Q --batch \
                       --eval "(progn
                                 (setq load-path (cons \"$(abs_srcdir)\" load-path)) 
                                 (setq load-path (cons nil load-path))
                                 (defun byte-compile-dest-file (f) \"$@\")
                                 (condition-case nil
                                   (byte-compile-file \"$<\")
                                   (error (kill-emacs 1))))"

(I have formatted the snippet for presentation, make probably won’t like it laid out this way.)

$(abs_srcdir) is being defined correctly, but I have two problems:

Firstly: With a directory layout like the following:

+- foo.el <- foo.el lives in $(abs_srcdir)
+- _build/
++- bar.el
++- Makefile

(That is, a VPATH build where foo.el lives in srcdir and I’m trying to build in _build.)

If bar.el depends on foo.el (via (require 'foo) and (provide 'foo)), attempts to compile bar.elc fail with the error:

In toplevel form:
../bar.el:1:1:Error: Cannot open load file: foo

This strikes me as odd because thought I was consing $(abs_srcdir) onto load-path. What’s happened?

The second problem is that even if this happens, emacs is exiting with status 0, despite my efforts to wrap the (byte-compile-file) call in a (condition-case). What has happened here?

Answer 1

The first problem I had was that with a VPATH build, files in the build directory weren’t being found (by calls to (require), for example). For some reason, consing nil onto load-path doesn’t work, but consing $(abs_srcdir) works.

The second problem was that I couldn’t catch the error raised by (byte-compile). This was solved by wvxvw: (byte-compile) doesn’t raise errors, but returns t if the compilation succeeds. Therefore, something like:

(unless (byte-compile-file "$<") (kill-emacs 1))

works nicely.