bpo-36721: Add --embed option to python-config (GH-13500)

To embed Python into an application, a new --embed option must be
passed to "python3-config --libs --embed" to get "-lpython3.8" (link
the application to libpython). To support both 3.8 and older, try
"python3-config --libs --embed" first and fallback to "python3-config
--libs" (without --embed) if the previous command fails.

Add a pkg-config "python-3.8-embed" module to embed Python into an
application: "pkg-config python-3.8-embed --libs" includes
"-lpython3.8".  To support both 3.8 and older, try "pkg-config
python-X.Y-embed --libs" first and fallback to "pkg-config python-X.Y
--libs" (without --embed) if the previous command fails (replace
"X.Y" with the Python version).

On the other hand, "pkg-config python3.8 --libs" no longer contains
"-lpython3.8". C extensions must not be linked to libpython (except
on Android, case handled by the script); this change is backward
incompatible on purpose.

"make install" now also installs "python-3.8-embed.pc".

5 files changed, 50 insertions, 6 deletions

diff --git a/Misc/NEWS.d/next/Build/2019-05-22-16-19-18.bpo-36721.9aRwfZ.rst b/Misc/NEWS.d/next/Build/2019-05-22-16-19-18.bpo-36721.9aRwfZ.rst
new file mode 100644
index 0000000000..1c266586a3
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2019-05-22-16-19-18.bpo-36721.9aRwfZ.rst
@@ -0,0 +1,16 @@
+To embed Python into an application, a new ``--embed`` option must be passed to
+``python3-config --libs --embed`` to get ``-lpython3.8`` (link the application
+to libpython). To support both 3.8 and older, try ``python3-config --libs
+--embed`` first and fallback to ``python3-config --libs`` (without ``--embed``)
+if the previous command fails.
+
+Add a pkg-config ``python-3.8-embed`` module to embed Python into an
+application: ``pkg-config python-3.8-embed --libs`` includes ``-lpython3.8``.
+To support both 3.8 and older, try ``pkg-config python-X.Y-embed --libs`` first
+and fallback to ``pkg-config python-X.Y --libs`` (without ``--embed``) if the
+previous command fails (replace ``X.Y`` with the Python version).
+
+On the other hand, ``pkg-config python3.8 --libs`` no longer contains
+``-lpython3.8``. C extensions must not be linked to libpython (except on
+Android, case handled by the script); this change is backward incompatible on
+purpose.
diff --git a/Misc/python-config.in b/Misc/python-config.in
index 1df30d261d..727c4a8682 100644
--- a/Misc/python-config.in
+++ b/Misc/python-config.in
@@ -9,7 +9,8 @@ import sys
 import sysconfig
 
 valid_opts = ['prefix', 'exec-prefix', 'includes', 'libs', 'cflags',
-              'ldflags', 'extension-suffix', 'help', 'abiflags', 'configdir']
+              'ldflags', 'extension-suffix', 'help', 'abiflags', 'configdir',
+              'embed']
 
 def exit_with_usage(code=1):
     print("Usage: {0} [{1}]".format(
@@ -47,8 +48,13 @@ for opt in opt_flags:
         print(' '.join(flags))
 
     elif opt in ('--libs', '--ldflags'):
-        libpython = getvar('LIBPYTHON')
-        libs = [libpython] if libpython else []
+        libs = []
+        if '--embed' in opt_flags:
+            libs.append('-lpython' + pyver + sys.abiflags)
+        else:
+            libpython = getvar('LIBPYTHON')
+            if libpython:
+                libs.append(libpython)
         libs.extend(getvar('LIBS').split() + getvar('SYSLIBS').split())
 
         # add the prefix/lib/pythonX.Y/config dir, but only if there is no
diff --git a/Misc/python-config.sh.in b/Misc/python-config.sh.in
index 33991ef0c5..59101d5a55 100644
--- a/Misc/python-config.sh.in
+++ b/Misc/python-config.sh.in
@@ -42,6 +42,7 @@ LIBC="@LIBC@"
 SYSLIBS="$LIBM $LIBC"
 ABIFLAGS="@ABIFLAGS@"
 LIBS="@LIBPYTHON@ @LIBS@ $SYSLIBS"
+LIBS_EMBED="-lpython${VERSION}${ABIFLAGS} @LIBS@ $SYSLIBS"
 BASECFLAGS="@BASECFLAGS@"
 LDLIBRARY="@LDLIBRARY@"
 OPT="@OPT@"
@@ -53,6 +54,7 @@ SO="@EXT_SUFFIX@"
 PYTHONFRAMEWORK="@PYTHONFRAMEWORK@"
 INCDIR="-I$includedir/python${VERSION}${ABIFLAGS}"
 PLATINCDIR="-I$includedir/python${VERSION}${ABIFLAGS}"
+PY_EMBED=0
 
 # Scan for --help or unknown argument.
 for ARG in $*
@@ -61,6 +63,9 @@ do
         --help)
             exit_with_usage 0
         ;;
+        --embed)
+            PY_EMBED=1
+        ;;
         --prefix|--exec-prefix|--includes|--libs|--cflags|--ldflags|--extension-suffix|--abiflags|--configdir)
         ;;
         *)
@@ -69,6 +74,10 @@ do
     esac
 done
 
+if [ $PY_EMBED = 1 ] ; then
+    LIBS="$LIBS_EMBED"
+fi
+
 for ARG in "$@"
 do
     case "$ARG" in
diff --git a/Misc/python-embed.pc.in b/Misc/python-embed.pc.in
new file mode 100644
index 0000000000..2be9df8143
--- /dev/null
+++ b/Misc/python-embed.pc.in
@@ -0,0 +1,13 @@
+# See: man pkg-config
+prefix=@prefix@
+exec_prefix=@exec_prefix@
+libdir=@libdir@
+includedir=@includedir@
+
+Name: Python
+Description: Embed Python into an application
+Requires:
+Version: @VERSION@
+Libs.private: @LIBS@
+Libs: -L${libdir} -lpython@VERSION@@ABIFLAGS@
+Cflags: -I${includedir}/python@VERSION@@ABIFLAGS@
diff --git a/Misc/python.pc.in b/Misc/python.pc.in
index ae698674bb..87e04decc2 100644
--- a/Misc/python.pc.in
+++ b/Misc/python.pc.in
@@ -5,9 +5,9 @@ libdir=@libdir@
 includedir=@includedir@
 
 Name: Python
-Description: Python library
-Requires: 
+Description: Build a C extension for Python
+Requires:
 Version: @VERSION@
 Libs.private: @LIBS@
-Libs: -L${libdir} -lpython@VERSION@@ABIFLAGS@
+Libs:
 Cflags: -I${includedir}/python@VERSION@@ABIFLAGS@