curl-config requires the bc command to work

[embray]

As we found out in #24919 (see ​https://trac.sagemath.org/ticket/24919#comment:63) the curl-config program that comes with curl, which we use to check the curl version, requires the standard bc command, which apparently on some systems is missing?

In a way this just means that the packaging of curl is broken since it should list bc as a runtime dependency. But we can work around that by checking for it ourselves.

This issue should be independent of #24919 since we already use curl-config to check for curl...

[dimpase]

This looks like a Debian bug, as I see this on Debian, and they package (lib)curl. By right, curl-config they ship must be fully functional, but it misses bc as a dependency.

I cc one of Debian people packaging Sagemath here.

[dimpase]

discussed with upstream on ​https://github.com/curl/curl/issues/3143 and upstream fixed it in ​https://github.com/curl/curl/pull/3174

[embray]

Thanks.

[embray]

I'm not sure what we should do in sage, if anything. I suppose it might still be worth adding an explicit check for the bc program when installing curl :(

[dimpase]

Replying to embray:

I'm not sure what we should do in sage, if anything. I suppose it might still be worth adding an explicit check for the bc program when installing curl :(

we could just make bc required in the top configure.ac, calling AC_CHECK_PROGRAM or whatever the right macro is.

[slelievre]

The upstream fix was merged in curl 7.62.0.

Rules for deciding whether to build curl are described in build/pkgs/curl/spkg-configure.m4.

Currently the approach is based on R's needs:

• build curl unless curl >= 7.22 is found.

Which of the following should we change it to?

• build curl unless curl >= 7.62 is found
• build curl unless either curl >= 7.62 is found or curl >= 7.22 and bc are found

[dimpase]

Currently we do not build curl if curl >= 7.22 (and, implcitly, bc - if the curl in question does need bc in its curl-config).

Adding an explicit check for bc (after our test for curl failed) would only improve error messages, but that's a rare event that a system has no bc installed.

Other potential improvements here would be to get rid of somewhat dodgy LIBCURL_CHECK_CONFIG and just use PKG_CHECK_MODULES (which doesn't need bc), or try PKG_CHECK_MODULES, and otherwise fall on LIBCURL_CHECK_CONFIG.

But all this is very minor.

[slelievre]

So maybe:

• check for curl >= 7.62: if found, good
• if not found, check for curl >= 7.22 and bc: if found, good
• if not found: build curl

[dimpase]

Replying to slelievre:

So maybe:

• check for curl >= 7.62: if found, good
• if not found, check for curl >= 7.22 and bc: if found, good
• if not found: build curl

please see my edits