cffi: Support --system-zstd

Support using the system zstd library with the CFFI backend.  Use
the GCC / Clang preprocessor output to find the paths to header files
for preprocessing.  Link to the system library, matching the behavior
for the C backend.

Signed-off-by: Michał Górny <mgorny@gentoo.org>

Author: mgorny

make_cffi.py

@@ -153,21 +153,45 @@ def normalize_output(output):
 
 
 def get_ffi(system_zstd = False):
-    here = os.path.abspath(os.path.dirname(__file__))
+    zstd_sources = []
+    include_dirs = []
+    libraries = []
 
-    zstd_sources = [
-        "zstd/zstd.c",
-    ]
+    if not system_zstd:
+        here = os.path.abspath(os.path.dirname(__file__))
 
-    # Headers whose preprocessed output will be fed into cdef().
-    headers = [
-        os.path.join(here, "zstd", p)
-        for p in ("zstd_errors.h", "zstd.h", "zdict.h")
-    ]
+        zstd_sources += [
+            "zstd/zstd.c",
+        ]
+
+        # Headers whose preprocessed output will be fed into cdef().
+        headers = [
+            os.path.join(here, "zstd", p)
+            for p in ("zstd_errors.h", "zstd.h", "zdict.h")
+        ]
 
-    include_dirs = [
-        os.path.join(here, "zstd"),
-    ]
+        include_dirs += [
+            os.path.join(here, "zstd"),
+        ]
+    else:
+        libraries += ["zstd"]
+
+        # Locate headers using the preprocessor.
+        include_re = re.compile(r'^# \d+ "([^"]+/(?:zstd_errors|zstd|zdict)\.h)"')
+        with tempfile.TemporaryDirectory() as temp_dir:
+            with open(os.path.join(temp_dir, "input.h"), "w") as f:
+                f.write("""
+#include <zstd_errors.h>
+#include <zstd.h>
+#include <zdict.h>
+""")
+            compiler.preprocess(os.path.join(temp_dir, "input.h"),
+                                os.path.join(temp_dir, "output.h"))
+            with open(os.path.join(temp_dir, "output.h"), "r") as f:
+                headers = list({
+                    m.group(1) for m in map(include_re.match, f)
+                    if m is not None
+                })
 
     # musl 1.1 doesn't define qsort_r. We need to force using the C90
     # variant.
@@ -195,6 +219,7 @@ def get_ffi(system_zstd = False):
         sources=zstd_sources,
         include_dirs=include_dirs,
         define_macros=define_macros,
+        libraries=libraries,
     )
 
     define = re.compile(rb"^#define\s+([a-zA-Z0-9_]+)\s+(\S+)")

setup.py

@@ -138,7 +138,7 @@
 if CFFI_BACKEND and cffi:
     import make_cffi
 
-    extensions.append(make_cffi.get_ffi().distutils_extension())
+    extensions.append(make_cffi.get_ffi(system_zstd=SYSTEM_ZSTD).distutils_extension())
 
 version = None