Add MSVC preprocessor support

.github/workflows/dist.yml

@@ -112,6 +112,10 @@ jobs:
     - name: Install test dependencies
       run: python -m pip --disable-pip-version-check install -r tests/requirements.txt
 
+    - name: Setup MSVC compiler
+      uses: ilammy/msvc-dev-cmd@v1
+      if: matrix.os == 'windows-latest'
+
     - name: Test wheel
       shell: bash
       run: |

cxxheaderparser/preprocessor.py

@@ -7,6 +7,7 @@
 import os
 import subprocess
 import sys
+import tempfile
 import typing
 
 from .options import PreprocessorFunction
@@ -104,6 +105,110 @@ def _preprocess_file(filename: str, content: typing.Optional[str]) -> str:
     return _preprocess_file
 
 
+#
+# Microsoft Visual Studio preprocessor support
+#
+
+
+def _msvc_filter(fp: typing.TextIO) -> str:
+    # MSVC outputs the original file as the very first #line directive
+    # so we just use that
+    new_output = io.StringIO()
+    keep = True
+
+    first = fp.readline()
+    assert first.startswith("#line")
+    fname = first[first.find('"') :]
+
+    for line in fp:
+        if line.startswith("#line"):
+            keep = line.endswith(fname)
+
+        if keep:
+            new_output.write(line)
+
+    new_output.seek(0)
+    return new_output.read()
+
+
+def make_msvc_preprocessor(
+    *,
+    defines: typing.List[str] = [],
+    include_paths: typing.List[str] = [],
+    retain_all_content: bool = False,
+    encoding: typing.Optional[str] = None,
+    msvc_args: typing.List[str] = ["cl.exe"],
+    print_cmd: bool = True,
+) -> PreprocessorFunction:
+    """
+    Creates a preprocessor function that uses cl.exe from Microsoft Visual Studio
+    to preprocess the input text. cl.exe is not typically on the path, so you
+    may need to open the correct developer tools shell or pass in the correct path
+    to cl.exe in the `msvc_args` parameter.
+
+    cl.exe will throw an error if a file referenced by an #include directive is not found.
+
+    :param defines: list of #define macros specified as "key value"
+    :param include_paths: list of directories to search for included files
+    :param retain_all_content: If False, only the parsed file content will be retained
+    :param encoding: If specified any include files are opened with this encoding
+    :param msvc_args: This is the path to cl.exe and any extra args you might want
+    :param print_cmd: Prints the command as its executed
+
+    .. code-block:: python
+
+        pp = make_msvc_preprocessor()
+        options = ParserOptions(preprocessor=pp)
+
+        parse_file(content, options=options)
+
+    """
+
+    if not encoding:
+        encoding = "utf-8"
+
+    def _preprocess_file(filename: str, content: typing.Optional[str]) -> str:
+        cmd = msvc_args + ["/nologo", "/E", "/C"]
+
+        for p in include_paths:
+            cmd.append(f"/I{p}")
+        for d in defines:
+            cmd.append(f"/D{d.replace(' ', '=')}")
+
+        tfpname = None
+
+        try:
+            kwargs = {"encoding": encoding}
+            if filename == "<str>":
+                if content is None:
+                    raise PreprocessorError("no content specified for stdin")
+
+                tfp = tempfile.NamedTemporaryFile(
+                    mode="w", encoding=encoding, suffix=".h", delete=False
+                )
+                tfpname = tfp.name
+                tfp.write(content)
+                tfp.close()
+
+                cmd.append(tfpname)
+            else:
+                cmd.append(filename)
+
+            if print_cmd:
+                print("+", " ".join(cmd), file=sys.stderr)
+
+            result: str = subprocess.check_output(cmd, **kwargs)  # type: ignore
+            if not retain_all_content:
+                result = _msvc_filter(io.StringIO(result))
+        finally:
+            if tfpname:
+                os.unlink(tfpname)
+
+        return result
+
+    return _preprocess_file
+
+
 #
 # PCPP preprocessor support (not installed by default)
 #

tests/test_preprocessor.py

@@ -26,7 +26,7 @@
 )
 
 
-@pytest.fixture(params=["gcc", "pcpp"])
+@pytest.fixture(params=["gcc", "msvc", "pcpp"])
 def make_pp(request) -> typing.Callable[..., PreprocessorFunction]:
     param = request.param
     if param == "gcc":
@@ -36,6 +36,12 @@ def make_pp(request) -> typing.Callable[..., PreprocessorFunction]:
 
         subprocess.run([gcc_path, "--version"])
         return preprocessor.make_gcc_preprocessor
+    elif param == "msvc":
+        gcc_path = shutil.which("cl.exe")
+        if not gcc_path:
+            pytest.skip("cl.exe not found")
+
+        return preprocessor.make_msvc_preprocessor
     elif param == "pcpp":
         if preprocessor.pcpp is None:
             pytest.skip("pcpp not installed")