bpo-45723: Detect missing pkg-config (GH-29442)

Author: tiran

Misc/NEWS.d/next/Build/2021-11-07-10-36-12.bpo-45723.JNwKSG.rst

@@ -0,0 +1 @@
+``configure`` now prints a warning when pkg-config is missing.

configure

@@ -2777,7 +2777,6 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
-
 if test "$srcdir" != . -a "$srcdir" != "$(pwd)"; then
     # If we're building out-of-tree, we need to make sure the following
     # resources get picked up before their $srcdir counterparts.
@@ -19574,6 +19573,11 @@ $SHELL $srcdir/Modules/makesetup -c $srcdir/Modules/config.c.in \
 			Modules/Setup.local $srcdir/Modules/Setup
 mv config.c Modules
 
+if test -z "$PKG_CONFIG"; then
+  echo "" >&6
+  echo "pkg-config is missing. Some dependencies may not be detected correctly." >&6
+fi
+
 if test "$Py_OPT" = 'false' -a "$Py_DEBUG" != 'true'; then
     echo "" >&6
     echo "" >&6

configure.ac

@@ -16,7 +16,12 @@ m4_ifdef(
     [AX_C_FLOAT_WORDS_BIGENDIAN],
     [],
     [AC_MSG_ERROR([Please install autoconf-archive package and re-run autoreconf])]
-)
+)dnl
+m4_ifdef(
+    [PKG_PROG_PKG_CONFIG],
+    [],
+    [AC_MSG_ERROR([Please install pkgconf's m4 macro package and re-run autoreconf])]
+)dnl
 
 AC_SUBST(BASECPPFLAGS)
 if test "$srcdir" != . -a "$srcdir" != "$(pwd)"; then
@@ -6114,6 +6119,11 @@ $SHELL $srcdir/Modules/makesetup -c $srcdir/Modules/config.c.in \
 			Modules/Setup.local $srcdir/Modules/Setup
 mv config.c Modules
 
+if test -z "$PKG_CONFIG"; then
+  echo "" >&AS_MESSAGE_FD
+  echo "pkg-config is missing. Some dependencies may not be detected correctly." >&AS_MESSAGE_FD
+fi
+
 if test "$Py_OPT" = 'false' -a "$Py_DEBUG" != 'true'; then
     echo "" >&AS_MESSAGE_FD
     echo "" >&AS_MESSAGE_FD