Index: clang/include/clang/Frontend/TextDiagnostic.h
===================================================================
--- clang/include/clang/Frontend/TextDiagnostic.h
+++ clang/include/clang/Frontend/TextDiagnostic.h
@@ -103,7 +103,8 @@
                            SmallVectorImpl<CharSourceRange> &Ranges,
                            ArrayRef<FixItHint> Hints);
 
-  void emitSnippet(StringRef SourceLine);
+  void emitSnippet(StringRef SourceLine, unsigned MaxLineNoDisplayWidth,
+                   unsigned LineNo);
 
   void emitParseableFixits(ArrayRef<FixItHint> Hints, const SourceManager &SM);
 };
Index: clang/lib/Frontend/TextDiagnostic.cpp
===================================================================
--- clang/lib/Frontend/TextDiagnostic.cpp
+++ clang/lib/Frontend/TextDiagnostic.cpp
@@ -1121,6 +1121,24 @@
   return FixItInsertionLine;
 }
 
+static unsigned getNumDisplayWidth(unsigned N) {
+  if (N < 10)
+    return 1;
+  if (N < 100)
+    return 2;
+  if (N < 1'000)
+    return 3;
+  if (N < 10'000)
+    return 4;
+  if (N < 100'000)
+    return 5;
+  if (N < 1'000'000)
+    return 6;
+  if (N < 10'000'000)
+    return 7;
+  return 0;
+}
+
 /// Emit a code snippet and caret line.
 ///
 /// This routine emits a single line's code snippet and caret line..
@@ -1174,6 +1192,10 @@
     if (auto OptionalRange = findLinesForRange(*I, FID, SM))
       Lines = maybeAddRange(Lines, *OptionalRange, MaxLines);
 
+  unsigned MaxLineNoDisplayWidth = std::max(getNumDisplayWidth(Lines.first),
+                                            getNumDisplayWidth(Lines.second));
+  unsigned HighlightIndent = MaxLineNoDisplayWidth + 4;
+
   for (unsigned LineNo = Lines.first; LineNo != Lines.second + 1; ++LineNo) {
     const char *BufStart = BufData.data();
     const char *BufEnd = BufStart + BufData.size();
@@ -1249,9 +1271,12 @@
       CaretLine.erase(CaretLine.end() - 1);
 
     // Emit what we have computed.
-    emitSnippet(SourceLine);
+    emitSnippet(SourceLine, MaxLineNoDisplayWidth, LineNo);
 
     if (!CaretLine.empty()) {
+      // Indent for line numbers
+      for (unsigned I = 0; I != HighlightIndent; ++I)
+        OS << ' ';
       if (DiagOpts->ShowColors)
         OS.changeColor(caretColor, true);
       OS << CaretLine << '\n';
@@ -1260,6 +1285,8 @@
     }
 
     if (!FixItInsertionLine.empty()) {
+      for (unsigned I = 0; I != HighlightIndent; ++I)
+        OS << ' ';
       if (DiagOpts->ShowColors)
         // Print fixit line in color
         OS.changeColor(fixitColor, false);
@@ -1275,7 +1302,8 @@
   emitParseableFixits(Hints, SM);
 }
 
-void TextDiagnostic::emitSnippet(StringRef line) {
+void TextDiagnostic::emitSnippet(StringRef line, unsigned MaxLineNoDisplayWidth,
+                                 unsigned LineNo) {
   if (line.empty())
     return;
 
@@ -1284,6 +1312,16 @@
   std::string to_print;
   bool print_reversed = false;
 
+  // Emit line number.
+  {
+    unsigned LineNoDisplayWidth = getNumDisplayWidth(LineNo);
+    OS << ' ';
+    for (unsigned I = LineNoDisplayWidth; I < MaxLineNoDisplayWidth; ++I)
+      OS << ' ';
+    OS << LineNo;
+    OS << " | ";
+  }
+
   while (i<line.size()) {
     std::pair<SmallString<16>,bool> res
         = printableTextForNextCharacter(line, &i, DiagOpts->TabStop);