Follow-up Comment #3, sr #110325 (project autoconf): > So, M4-level `dnl` comments are one thing, but how about shell-level `#` comments?
Fun fact: `dnl ...` is _not_ a comment as far as M4 is concerned, but `# ...` _is_ ! See https://www.gnu.org/savannah-checkouts/gnu/m4/manual/html_node/Comments.html and https://www.gnu.org/savannah-checkouts/gnu/m4/manual/html_node/Dnl.html . We don't usually think of `# ...` as a M4 comment because it's included in the output, but the thing is, it's included in the output _verbatim_. An unquoted `#` (or more precisely, whatever the current "begin-comment delimiter" string is, see https://www.gnu.org/savannah-checkouts/gnu/m4/manual/html_node/Changecom.html ) tells M4 to copy text to the output (or current diversion) _without macro expansion_ from that point until the end of the line (current "end-comment delimiter"). `dnl`, by contrast, is a built-in macro with abnormal argument syntax, and it can be disabled just like any other built-in macro. People _use_ it for comments that they want stripped from the M4 output, but that's not what it was included in M4 for originally -- its actual design purpose is to join input lines (hence the acronym, "delete [the following] new line"). The bug here is precisely that autoupdate wants to preserve `dnl ...` comments in its output, but has no way to do so without also subjecting the `...` to macro expansion. This is what I meant by "a new feature in M4 itself -- allowing more than one comment starter to be active at once": if undefine([dnl]) changecom([#],[ ],[dnl],[ ]) meant that _either_ `#` _or_ `dnl` began an M4-style comment -- copied verbatim to the output -- running until the end of the line, then autoupdate could use that to DTRT with the original test case. > my style decision to combine the two into `dnl#` comments I believe this stylistic change will also work around this particular bug in autoupdate, yes, except that you might want to double-check that it doesn't cause this dnl# Check for the headers we need AC_CHECK_HEADERS_ONCE([foo.h bar.h]) to turn into nothing at all (i.e. the AC_CHECK_HEADERS_ONCE line is lost) when processed by either normal autoconf or autoupdate. _______________________________________________________ Reply to this item at: <https://savannah.gnu.org/support/?110325> _______________________________________________ Message sent via Savannah https://savannah.gnu.org/
