Re: Issue 187: "Configure should stop when no compiler is found"

Hi Alex,

Thanks for the suggestions.

On Sat, Oct 05, 2024 at 01:28:57PM +0200, [email protected] wrote:
>Hi Rodrigo,
>
>Regarding this issue[1], I have found couple of ways to address this:
>
>The easiest way is to do AC_PROG_CXX before AC_PROG_CC:
>
>--- a/configure.ac	Sat Oct  5 13:15:28 2024
>+++ b/configure.ac	Sat Oct  5 13:15:48 2024
>@@ -124,8 +124,8 @@ if test "x$enable_ssl" != "x"; then
>   AC_MSG_ERROR([The flag --enable-ssl is deprecated, use --enable-tls])
> fi
>
>-AC_PROG_CC
> AC_PROG_CXX
>+AC_PROG_CC
> AC_PROG_RANLIB
> AC_PROG_CPP
>
>Which now errors out when no working compiler is found:
>'configure: error: C++ compiler cannot create executables'

I think it relies on a detail of the implementation, so I don't think we 
can trust it to always work.

I cannot believe that in 2024 it is still not considered a bug...

>Alternately, we can add a check to verify if the complier actually
>exists, and if not, exit. Something like this:
>
>dnl ------------------------------------------------------------
>dnl AC_PROG_CXX will set CXX=g++ even if it finds no useable C++
>dnl compiler, so we have to check whether the program named by
>dnl CXX exists.
>dnl ------------------------------------------------------------
>dnl
>AC_PROG_CXX
>AC_PATH_PROG(REAL_CXX, $CXX)
>HAVE_CXX=no
>if test -n "$REAL_CXX"; then
>	HAVE_CXX=yes
>fi
>if HAVE_CXX="no"; then
>	echo "Error: No working C++ compiler found!"
>	exit 1
>	fi

This is probably better, but even if the C++ compiler is in the path, it 
doesn't mean it actually works.

I think something like this may be more strict, as we test that it can 
compile a simple C++ program:

diff --git a/configure.ac b/configure.ac
index 5c308cb7..7d156b81 100644
--- a/configure.ac
+++ b/configure.ac
@@ -129,6 +129,19 @@ AC_PROG_CXX
  AC_PROG_RANLIB
  AC_PROG_CPP

+AC_MSG_CHECKING(if C++ compiler '$CXX' works)
+AC_LANG_PUSH([C++])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+  #ifndef __cplusplus
+  #error "No C++ support, AC_PROG_CXX failed"
+  #endif
+  ]])],
+  [AC_MSG_RESULT([yes])],
+  [AC_MSG_RESULT(no)
+  AC_MSG_FAILURE([C++ compiler doesn't work])]
+)
+AC_LANG_POP([C++])
+
  dnl ----------------------------
  dnl Check our char and int types
  dnl ----------------------------


Outputs this when configured with the non-existent iguana C++ compiler:

$ ../configure CXX=iguana
...
checking whether the compiler supports GNU C++... no
checking whether iguana accepts -g... no
checking for iguana option to enable C++11 features... unsupported
checking for iguana option to enable C++98 features... unsupported
checking dependency style of iguana... none
checking for ranlib... ranlib
checking how to run the C preprocessor... gcc -E
checking if C++ compiler 'iguana' works... no
configure: error: in '/home/ram/dev/dillo/git/build':
configure: error: C++ compiler doesn't work
See 'config.log' for more details

Best,
Rodrigo.
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