[llvm] Implement a custom stream for LDBG macro to handle newlines (PR #150750)

[Mehdi Amini via llvm-commits]

================
@@ -26,55 +26,105 @@ namespace llvm {
 //              << "] " << "Bitset contains: " << Bitset << "\n");
 #define LDBG() DEBUGLOG_WITH_STREAM_AND_TYPE(llvm::dbgs(), DEBUG_TYPE)
 
-#if defined(__SHORT_FILE__)
-#define DEBUGLOG_WITH_STREAM_AND_TYPE(STREAM, TYPE)                            \
+#define DEBUGLOG_WITH_STREAM_TYPE_AND_FILE(STREAM, TYPE, FILE)                 \
   for (bool _c = (::llvm::DebugFlag && ::llvm::isCurrentDebugType(TYPE)); _c;  \
        _c = false)                                                             \
-  ::llvm::impl::LogWithNewline(TYPE, __SHORT_FILE__, __LINE__, (STREAM))
+  ::llvm::impl::raw_ldbg_ostream{                                              \
+      ::llvm::impl::computePrefix(TYPE, FILE, __LINE__), (STREAM)}             \
+      .asLvalue()
+// When __SHORT_FILE__ is not defined, the File is the full path,
+// otherwise __SHORT_FILE__ is defined in CMake to provide the file name
+// without the path prefix.
+#if defined(__SHORT_FILE__)
+#define DEBUGLOG_WITH_STREAM_AND_TYPE(STREAM, TYPE)                            \
+  DEBUGLOG_WITH_STREAM_TYPE_AND_FILE(STREAM, TYPE, __SHORT_FILE__)
 #else
 #define DEBUGLOG_WITH_STREAM_AND_TYPE(STREAM, TYPE)                            \
-  for (bool _c = (::llvm::DebugFlag && ::llvm::isCurrentDebugType(TYPE)); _c;  \
-       _c = false)                                                             \
-  ::llvm::impl::LogWithNewline(TYPE, __FILE__, __LINE__, (STREAM))
+  DEBUGLOG_WITH_STREAM_TYPE_AND_FILE(                                          \
+      STREAM, TYPE, ::llvm::impl::LogWithNewline::getShortFileName(__FILE__))
 #endif
 
 namespace impl {
-class LogWithNewline {
-public:
-  LogWithNewline(const char *debug_type, const char *file, int line,
-                 raw_ostream &os)
-      : os(os) {
-#if !defined(__SHORT_FILE__)
-    file = ::llvm::impl::LogWithNewline::getShortFileName(file);
-#endif
-    if (debug_type)
-      os << "[" << debug_type << "] ";
-    os << file << ":" << line << " ";
+
+/// A raw_ostream that tracks `\n` and print the prefix.
+class LLVM_ABI raw_ldbg_ostream final : public raw_ostream {
+  std::string Prefix;
+  raw_ostream &Os;
+  bool HasPendingNewline = true;
+
+  /// Split the line on newlines and insert the prefix before each newline.
+  /// Forward everything to the underlying stream.
+  void write_impl(const char *Ptr, size_t Size) final {
+    auto Str = StringRef(Ptr, Size);
+    // Handle the initial prefix.
+    if (!Str.empty())
----------------
joker-eph wrote:

There is a check for HasPendingNewline inside the implementation of writeWithPrefix, your check is redundant.

https://github.com/llvm/llvm-project/pull/150750