cffi: Move CFFI logic from global scope into get_ffi() function

Move the CFFI-related logic from the global scope of `make_cffi.py`
file to a `get_ffi()` function.  This makes it possible to import
the file without executing the code immediately, and it will make it
possible to parametrize the invocation using explicit function
parameters.  Along with the change, I've renamed the variables to
lowercase since they are no longer global.

Author: mgorny

make_cffi.py

@@ -15,19 +15,6 @@
 
 import cffi
 
-HERE = os.path.abspath(os.path.dirname(__file__))
-
-SOURCES = [
-    "zstd/zstd.c",
-]
-
-# Headers whose preprocessed output will be fed into cdef().
-HEADERS = [os.path.join(HERE, "zstd", p) for p in ("zstd.h", "zdict.h")]
-
-INCLUDE_DIRS = [
-    os.path.join(HERE, "zstd"),
-]
-
 # cffi can't parse some of the primitives in zstd.h. So we invoke the
 # preprocessor and feed its output into cffi.
 compiler = distutils.ccompiler.new_compiler()
@@ -158,59 +145,75 @@ def normalize_output(output):
     return b"\n".join(lines)
 
 
-ffi = cffi.FFI()
-# zstd.h uses a possible undefined MIN(). Define it until
-# https://github.com/facebook/zstd/issues/976 is fixed.
-# *_DISABLE_DEPRECATE_WARNINGS prevents the compiler from emitting a warning
-# when cffi uses the function. Since we statically link against zstd, even
-# if we use the deprecated functions it shouldn't be a huge problem.
-ffi.set_source(
-    "zstandard._cffi",
-    """
-#define MIN(a,b) ((a)<(b) ? (a) : (b))
-#define ZSTD_STATIC_LINKING_ONLY
-#define ZSTD_DISABLE_DEPRECATE_WARNINGS
-#include <zstd.h>
-#define ZDICT_STATIC_LINKING_ONLY
-#define ZDICT_DISABLE_DEPRECATE_WARNINGS
-#include <zdict.h>
-""",
-    sources=SOURCES,
-    include_dirs=INCLUDE_DIRS,
-)
-
-DEFINE = re.compile(b"^\\#define ([a-zA-Z0-9_]+) ")
-
-sources = []
-
-# Feed normalized preprocessor output for headers into the cdef parser.
-for header in HEADERS:
-    preprocessed = preprocess(header)
-    sources.append(normalize_output(preprocessed))
-
-    # #define's are effectively erased as part of going through preprocessor.
-    # So perform a manual pass to re-add those to the cdef source.
-    with open(header, "rb") as fh:
-        for line in fh:
-            line = line.strip()
-            m = DEFINE.match(line)
-            if not m:
-                continue
+def get_ffi():
+    here = os.path.abspath(os.path.dirname(__file__))
+
+    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.h", "zdict.h")]
+
+    include_dirs = [
+        os.path.join(here, "zstd"),
+    ]
+
+    ffi = cffi.FFI()
+    # zstd.h uses a possible undefined MIN(). Define it until
+    # https://github.com/facebook/zstd/issues/976 is fixed.
+    # *_DISABLE_DEPRECATE_WARNINGS prevents the compiler from emitting a warning
+    # when cffi uses the function. Since we statically link against zstd, even
+    # if we use the deprecated functions it shouldn't be a huge problem.
+    ffi.set_source(
+        "zstandard._cffi",
+        """
+    #define MIN(a,b) ((a)<(b) ? (a) : (b))
+    #define ZSTD_STATIC_LINKING_ONLY
+    #define ZSTD_DISABLE_DEPRECATE_WARNINGS
+    #include <zstd.h>
+    #define ZDICT_STATIC_LINKING_ONLY
+    #define ZDICT_DISABLE_DEPRECATE_WARNINGS
+    #include <zdict.h>
+    """,
+        sources=zstd_sources,
+        include_dirs=include_dirs,
+    )
 
-            if m.group(1) == b"ZSTD_STATIC_LINKING_ONLY":
-                continue
+    DEFINE = re.compile(b"^\\#define ([a-zA-Z0-9_]+) ")
 
-            # The parser doesn't like some constants with complex values.
-            if m.group(1) in (b"ZSTD_LIB_VERSION", b"ZSTD_VERSION_STRING"):
-                continue
+    sources = []
+
+    # Feed normalized preprocessor output for headers into the cdef parser.
+    for header in headers:
+        preprocessed = preprocess(header)
+        sources.append(normalize_output(preprocessed))
+
+        # #define's are effectively erased as part of going through preprocessor.
+        # So perform a manual pass to re-add those to the cdef source.
+        with open(header, "rb") as fh:
+            for line in fh:
+                line = line.strip()
+                m = DEFINE.match(line)
+                if not m:
+                    continue
+
+                if m.group(1) == b"ZSTD_STATIC_LINKING_ONLY":
+                    continue
+
+                # The parser doesn't like some constants with complex values.
+                if m.group(1) in (b"ZSTD_LIB_VERSION", b"ZSTD_VERSION_STRING"):
+                    continue
+
+                # The ... is magic syntax by the cdef parser to resolve the
+                # value at compile time.
+                sources.append(m.group(0) + b" ...")
 
-            # The ... is magic syntax by the cdef parser to resolve the
-            # value at compile time.
-            sources.append(m.group(0) + b" ...")
+    cdeflines = b"\n".join(sources).splitlines()
+    cdeflines = [line for line in cdeflines if line.strip()]
+    ffi.cdef(b"\n".join(cdeflines).decode("latin1"))
+    return ffi
 
-cdeflines = b"\n".join(sources).splitlines()
-cdeflines = [line for line in cdeflines if line.strip()]
-ffi.cdef(b"\n".join(cdeflines).decode("latin1"))
 
 if __name__ == "__main__":
-    ffi.compile()
+    get_ffi().compile()

setup.py

@@ -112,7 +112,7 @@
 if CFFI_BACKEND and cffi:
     import make_cffi
 
-    extensions.append(make_cffi.ffi.distutils_extension())
+    extensions.append(make_cffi.get_ffi().distutils_extension())
 
 version = None