Make aspect MSVC compatible

src/aspect/dwyu.bzl

@@ -76,12 +76,15 @@ def extract_defines_from_compiler_flags(compiler_flags):
     defines = {}
 
     for cflag in compiler_flags:
-        if cflag.startswith("-U"):
+        # gcc/clang use '-U'. MSVC uses '/U'.
+        if cflag.startswith(("-U", "/U")):
             undefine = cflag[2:]
             undefine_name = undefine.split("=", 1)[0]
             if undefine_name in defines.keys():
                 defines.pop(undefine_name)
-        if cflag.startswith("-D"):
+
+        # gcc/clang use '-D'. MSVC uses '/D'.
+        if cflag.startswith(("-D", "/D")):
             define = cflag[2:]
             define_name = define.split("=", 1)[0]
             defines[define_name] = define

src/aspect/test/dwyu_test.bzl

@@ -29,6 +29,13 @@ def _extract_defines_from_compiler_flags_test_impl(ctx):
         extract_defines_from_compiler_flags(["-DFoo=BAR=42", "-DTick 42", '-DRiff "Raff"']),
     )
 
+    # MSVC syntax
+    asserts.equals(
+        env,
+        ["Bar", "FooBar=42"],
+        extract_defines_from_compiler_flags(["/DFoo", "/UFoo", "/DBar", "/DFooBar=42"]),
+    )
+
     return unittest.end(env)
 
 extract_defines_from_compiler_flags_test = unittest.make(_extract_defines_from_compiler_flags_test_impl)

test/aspect/defines/BUILD

@@ -7,7 +7,11 @@ cc_library(
 cc_library(
     name = "defines_from_bazel_target",
     hdrs = ["defines_from_bazel_target.h"],
-    copts = ["-DSOME_COPT 42"],
+    copts = select({
+        # Strictly speaking Windows does not automatically equal MSVC, but does so in our integration tests
+        "@platforms//os:windows": ["/DSOME_COPT 42"],
+        "//conditions:default": ["-DSOME_COPT 42"],
+    }),
     defines = ["SOME_DEFINE"],
     local_defines = ["LOCAL_DEFINE"],
     deps = ["//defines/support:lib_a"],