[clang][scandeps] Improve handling of rawstrings.

The current parser just checks one step back for a R before each string
to know that it's a rawstring. But the preprocessor is much more
advanced here and can have constructs like:

R\
"str"

And much more. This patch also adds more test coverage for Rawstrings in
the dependencydirectivesscanner.

This was co-authored by Sylvain Audi <[email protected]>

Fixes #137648

Author: tru

clang/lib/Lex/DependencyDirectivesScanner.cpp

@@ -206,6 +206,24 @@ static void skipOverSpaces(const char *&First, const char *const End) {
     ++First;
 }
 
+// Move back by one character, skipping escaped newlines (backslash + \n)
+static char previousChar(const char *First, const char *&Current) {
+  assert(Current > First);
+  --Current;
+  while (Current > First + 1 && isVerticalWhitespace(*Current)) {
+    const char PrevChar = *(Current - 1);
+    if (PrevChar == '\\') {
+      Current -= 2; // backslash + (\n or \r)
+    } else if (Current > First + 2 && isVerticalWhitespace(PrevChar) &&
+               PrevChar != *Current && *(Current - 2) == '\\') {
+      Current -= 3; // backslash + (\n\r or \r\n)
+    } else {
+      break;
+    }
+  }
+  return *Current;
+}
+
 [[nodiscard]] static bool isRawStringLiteral(const char *First,
                                              const char *Current) {
   assert(First <= Current);
@@ -215,25 +233,28 @@ static void skipOverSpaces(const char *&First, const char *const End) {
     return false;
 
   // Check for an "R".
-  --Current;
-  if (*Current != 'R')
+  if (previousChar(First, Current) != 'R')
     return false;
-  if (First == Current || !isAsciiIdentifierContinue(*--Current))
+  if (First == Current ||
+      !isAsciiIdentifierContinue(previousChar(First, Current)))
     return true;
 
   // Check for a prefix of "u", "U", or "L".
   if (*Current == 'u' || *Current == 'U' || *Current == 'L')
-    return First == Current || !isAsciiIdentifierContinue(*--Current);
+    return First == Current ||
+           !isAsciiIdentifierContinue(previousChar(First, Current));
 
   // Check for a prefix of "u8".
-  if (*Current != '8' || First == Current || *Current-- != 'u')
+  if (*Current != '8' || First == Current ||
+      previousChar(First, Current) != 'u')
     return false;
-  return First == Current || !isAsciiIdentifierContinue(*--Current);
+  return First == Current ||
+         !isAsciiIdentifierContinue(previousChar(First, Current));
 }
 
 static void skipRawString(const char *&First, const char *const End) {
   assert(First[0] == '"');
-  assert(First[-1] == 'R');
+  //assert(First[-1] == 'R');
 
   const char *Last = ++First;
   while (Last != End && *Last != '(')
@@ -416,6 +437,14 @@ void Scanner::skipLine(const char *&First, const char *const End) {
         continue;
       }
 
+      // Continue on the same line if an EOL is preceded with backslash
+      if (First + 1 < End && *First == '\\') {
+        if (unsigned Len = isEOL(First + 1, End)) {
+          First += 1 + Len;
+          continue;
+        }
+      }
+
       // Iterate over comments correctly.
       if (*First != '/' || End - First < 2) {
         LastTokenPtr = First;

clang/test/ClangScanDeps/raw-strings.cpp

@@ -0,0 +1,55 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: sed -e "s|DIR|%/t|g" %t/cdb.json.in > %t/cdb.json
+
+//--- cdb.json.in
+[{
+    "directory": "DIR",
+    "command": "clang -c DIR/tu.c -o DIR/tu.o -IDIR/include",
+    "file": "DIR/tu.c"
+}]
+//--- include/header.h
+//--- include/header2.h
+//--- include/header3.h
+//--- include/header4.h
+//--- tu.c
+#if 0
+R"x()x"
+#endif
+
+#include "header.h"
+
+#if 0
+R"y(";
+#endif
+#include "header2.h"
+
+#if 0
+//")y"
+#endif
+
+#if 0
+R"y(";
+R"z()y";
+#endif
+#include "header3.h"
+#if 0
+//")z"
+#endif
+
+#if 0
+R\
+"y(";
+R"z()y";
+#endif
+#include "header4.h"
+#if 0
+//")z"
+#endif
+
+// RUN: clang-scan-deps -compilation-database %t/cdb.json -mode preprocess | FileCheck %s
+// RUN: clang-scan-deps -compilation-database %t/cdb.json -mode preprocess-dependency-directives | FileCheck %s
+// CHECK: tu.c
+// CHECK-NEXT: header.h
+// CHECK-NEXT: header3.h
+// CHECK-NEXT: header4.h