[GRASS-dev] another make problem (OSX, but could be a general problem)

[Glynn Clements]

Glynn Clements wrote:

> sqlp *might* be due to lex/yacc issues (that's the only part that's
> different from other libraries).

It was due to lex/yacc issues.

> If yacc is being re-run, y.tab.h will
> be updated, which will force the rest of it to be compiled.

What was happening is that Rules.make has:

	ifndef LOCAL_HEADERS
	LOCAL_HEADERS = $(wildcard *.h)
	endif
and:
	$(OBJDIR)/%.o : %.c $(LOCAL_HEADERS) | $(OBJDIR)

On initial compilation, y.tab.h doesn't exist, so it isn't included in
$(LOCAL_HEADERS).

[This is a common pitfall of using $(wildcard ...). It only returns
what exists right now, omitting files which may be generated later.]

If $(OBJDIR)/y.tab.o isn't the first object file, then y.tab.h may[1]
end up being newer than some of the object files. On a second run,
y.tab.h is now a dependency for all object files, so any which are
older than y.tab.h will be re-compiled.

[1] File timestamps typically have a resolution of one second, so it's
probabilistic as to whether it's actually older.

The fix was to add $(EXTRA_HEADERS) as a dependency of $(OBJDIR)/%.o,
so that y.tab.h can be added even when it doesn't exist. This will
force y.tab.h to be generated before any of the object files, so
y.tab.h will be older.

-- 
Glynn Clements <glynn at gclements.plus.com>