[clang][deps] Don't treat ObjC method args as module directives

`import:(type)name` is a method argument decl in ObjC, but the C++20
preprocessing rules say this is a preprocessing line.

Because the dependency directive scanner is not language dependent,
this patch extends the C++20 rule to exclude `module :` (which is
never a valid module decl anyway), and `import :` that is not followed
by an identifier.

This is ok to do because in C++20 mode the compiler will later error
on lines like this anyway, and the dependencies the scanner returns
are still correct.

Author: Bigcheese

clang/lib/Lex/DependencyDirectivesScanner.cpp

@@ -660,7 +660,18 @@ bool Scanner::lexModule(const char *&First, const char *const End) {
   // an import.
 
   switch (*First) {
-  case ':':
+  case ':': {
+    // `module :` is never the start of a valid module declaration.
+    if (Id == "module") {
+      skipLine(First, End);
+      return false;
+    }
+    // `import:(type)name` is a valid ObjC method decl, so check one more token.
+    (void)lexToken(First, End);
+    if (!tryLexIdentifierOrSkipLine(First, End))
+      return false;
+    break;
+  }
   case '<':
   case '"':
     break;

clang/test/ClangScanDeps/scanner-objc-compat.m

@@ -0,0 +1,28 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: clang-scan-deps -format experimental-full -- \
+// RUN:   %clang -c %t/main.m -o %t/main.o -fmodules -I %t > %t/deps.db
+// RUN: cat %t/deps.db | sed 's:\\\\\?:/:g' | FileCheck %s -DPREFIX=%/t
+
+// Verify that the scanner does not treat ObjC method decls with arguments named
+// module or import as module/import decls.
+
+// CHECK: "module-name": "A"
+
+//--- A.h
+
+@interface SomeObjcClass
+  - (void)func:(int)otherData
+          module:(int)module
+          import:(int)import;
+@end
+
+//--- module.modulemap
+
+module A {
+  header "A.h"
+}
+
+//--- main.m
+
+#include "A.h"