Index: lib/Format/BreakableToken.cpp
===================================================================
--- lib/Format/BreakableToken.cpp
+++ lib/Format/BreakableToken.cpp
@@ -67,10 +67,11 @@
                                              unsigned ContentStartColumn,
                                              unsigned ColumnLimit,
                                              unsigned TabWidth,
-                                             encoding::Encoding Encoding) {
-  LLVM_DEBUG(llvm::dbgs() << "Comment split: \"" << Text << ", " << ColumnLimit
-                          << "\", Content start: " << ContentStartColumn
-                          << "\n");
+                                             encoding::Encoding Encoding,
+                                             const FormatStyle &Style) {
+  LLVM_DEBUG(llvm::dbgs() << "Comment split: \"" << Text
+                          << "\", Column limit: " << ColumnLimit
+                          << ", Content start: " << ContentStartColumn << "\n");
   if (ColumnLimit <= ContentStartColumn + 1)
     return BreakableToken::Split(StringRef::npos, 0);
 
@@ -95,6 +96,13 @@
   if (SpaceOffset != StringRef::npos &&
       kNumberedListRegexp->match(Text.substr(SpaceOffset).ltrim(Blanks)))
     SpaceOffset = Text.find_last_of(Blanks, SpaceOffset);
+  // In JavaScript, some @tags can be followed by {, and machinery that parses
+  // these comments will fail to understand the comment if followed by a line
+  // break. So avoid ever breaking before a {.
+  if (Style.Language == FormatStyle::LK_JavaScript &&
+      SpaceOffset != StringRef::npos && SpaceOffset + 1 < Text.size() &&
+      Text[SpaceOffset + 1] == '{')
+    SpaceOffset = Text.find_last_of(Blanks, SpaceOffset);
 
   if (SpaceOffset == StringRef::npos ||
       // Don't break at leading whitespace.
@@ -109,6 +117,12 @@
         Blanks, std::max<unsigned>(MaxSplitBytes, FirstNonWhitespace));
   }
   if (SpaceOffset != StringRef::npos && SpaceOffset != 0) {
+    // adaptStartOfLine will break after lines starting with /** if the comment
+    // is broken anywhere. Avoid emitting this break twice here.
+    // Example: in /** longtextcomesherethatbreaks */ (with ColumnLimit 20) will
+    // insert a break after /**, so this code must not insert the same break.
+    if (SpaceOffset == 1 && Text[SpaceOffset - 1] == '*')
+      return BreakableToken::Split(StringRef::npos, 0);
     StringRef BeforeCut = Text.substr(0, SpaceOffset).rtrim(Blanks);
     StringRef AfterCut = Text.substr(SpaceOffset).ltrim(Blanks);
     return BreakableToken::Split(BeforeCut.size(),
@@ -260,7 +274,7 @@
     return Split(StringRef::npos, 0);
   return getCommentSplit(Content[LineIndex].substr(TailOffset),
                          ContentStartColumn, ColumnLimit, Style.TabWidth,
-                         Encoding);
+                         Encoding, Style);
 }
 
 void BreakableComment::compressWhitespace(
@@ -620,6 +634,8 @@
     if (DelimitersOnNewline) {
       // Since we're breaking at index 1 below, the break position and the
       // break length are the same.
+      // Note: this works because getCommentSplit is careful never to split at
+      // the beginning of a line.
       size_t BreakLength = Lines[0].substr(1).find_first_not_of(Blanks);
       if (BreakLength != StringRef::npos)
         insertBreak(LineIndex, 0, Split(1, BreakLength), /*ContentIndent=*/0,
Index: unittests/Format/FormatTestComments.cpp
===================================================================
--- unittests/Format/FormatTestComments.cpp
+++ unittests/Format/FormatTestComments.cpp
@@ -1254,6 +1254,12 @@
                    " */",
                    getLLVMStyleWithColumns(20)));
 
+  // This reproduces a crashing bug where both adaptStartOfLine and
+  // getCommentSplit were trying to wrap after the "/**".
+  EXPECT_EQ("/** multilineblockcommentwithnowrapopportunity */",
+            format("/** multilineblockcommentwithnowrapopportunity */",
+                   getLLVMStyleWithColumns(20)));
+
   EXPECT_EQ("/*\n"
             "\n"
             "\n"
Index: unittests/Format/FormatTestJS.cpp
===================================================================
--- unittests/Format/FormatTestJS.cpp
+++ unittests/Format/FormatTestJS.cpp
@@ -191,31 +191,32 @@
 
   // Break a single line long jsdoc comment pragma.
   EXPECT_EQ("/**\n"
-            " * @returns\n"
-            " *     {string}\n"
-            " *     jsdoc line 12\n"
+            " * @returns {string} jsdoc line 12\n"
             " */",
             format("/** @returns {string} jsdoc line 12 */",
                    getGoogleJSStyleWithColumns(20)));
-
   EXPECT_EQ("/**\n"
-            " * @returns\n"
-            " *     {string}\n"
+            " * @returns {string}\n"
             " *     jsdoc line 12\n"
             " */",
+            format("/** @returns {string} jsdoc line 12 */",
+                   getGoogleJSStyleWithColumns(25)));
+
+  EXPECT_EQ("/**\n"
+            " * @returns {string} jsdoc line 12\n"
+            " */",
             format("/** @returns {string} jsdoc line 12  */",
                    getGoogleJSStyleWithColumns(20)));
 
   // FIXME: this overcounts the */ as a continuation of the 12 when breaking.
   // Related to the FIXME in BreakableBlockComment::getRangeLength.
   EXPECT_EQ("/**\n"
-            " * @returns\n"
-            " *     {string}\n"
-            " *     jsdoc line\n"
+            " * @returns {string}\n"
+            " *     jsdoc line line\n"
             " *     12\n"
             " */",
-            format("/** @returns {string} jsdoc line 12*/",
-                   getGoogleJSStyleWithColumns(20)));
+            format("/** @returns {string} jsdoc line line 12*/",
+                   getGoogleJSStyleWithColumns(25)));
 
   // Fix a multiline jsdoc comment ending in a comment pragma.
   EXPECT_EQ("/**\n"
@@ -2038,27 +2039,32 @@
 
 TEST_F(FormatTestJS, JSDocAnnotations) {
   verifyFormat("/**\n"
-               " * @exports\n"
-               " *     {this.is.a.long.path.to.a.Type}\n"
+               " * @exports {this.is.a.long.path.to.a.Type}\n"
                " */",
                "/**\n"
                " * @exports {this.is.a.long.path.to.a.Type}\n"
                " */",
                getGoogleJSStyleWithColumns(20));
   verifyFormat("/**\n"
-               " * @mods\n"
-               " *     {this.is.a.long.path.to.a.Type}\n"
+               " * @mods {this.is.a.long.path.to.a.Type}\n"
+               " */",
+               "/**\n"
+               " * @mods {this.is.a.long.path.to.a.Type}\n"
+               " */",
+               getGoogleJSStyleWithColumns(20));
+  verifyFormat("/**\n"
+               " * @mods {this.is.a.long.path.to.a.Type}\n"
                " */",
                "/**\n"
                " * @mods {this.is.a.long.path.to.a.Type}\n"
                " */",
                getGoogleJSStyleWithColumns(20));
   verifyFormat("/**\n"
-               " * @param\n"
-               " *     {this.is.a.long.path.to.a.Type}\n"
+               " * @param {canWrap\n"
+               " *     onSpace}\n"
                " */",
                "/**\n"
-               " * @param {this.is.a.long.path.to.a.Type}\n"
+               " * @param {canWrap onSpace}\n"
                " */",
                getGoogleJSStyleWithColumns(20));
   verifyFormat("/**\n"
@@ -2083,8 +2089,7 @@
             "  /**\n"
             "   * long long long\n"
             "   * long\n"
-            "   * @param\n"
-            "   *     {this.is.a.long.path.to.a.Type}\n"
+            "   * @param {this.is.a.long.path.to.a.Type}\n"
             "   *     a\n"
             "   * long long long\n"
             "   * long long\n"