From 7c8ef74bd5aeab5694c481832fb8cc42e891f828 Mon Sep 17 00:00:00 2001
From: Adriaan Moors <adriaan@lightbend.com>
Date: Wed, 19 Oct 2016 12:56:08 -0700
Subject: Keep `skipBlockComment` tail recursive

Avoid StackOverflow on big comments.
Simplify `ScaladocJavaUnitScanner` while in there.

TODO: Do same for `ScaladocUnitScanner`?
---
 .../scala/tools/nsc/javac/JavaScanners.scala       | 26 +++++++++----
 .../scala/tools/nsc/doc/ScaladocAnalyzer.scala     | 43 ++++++----------------
 2 files changed, 30 insertions(+), 39 deletions(-)

diff --git a/src/compiler/scala/tools/nsc/javac/JavaScanners.scala b/src/compiler/scala/tools/nsc/javac/JavaScanners.scala
index e11ac94041..bf944f1eda 100644
--- a/src/compiler/scala/tools/nsc/javac/JavaScanners.scala
+++ b/src/compiler/scala/tools/nsc/javac/JavaScanners.scala
@@ -577,27 +577,37 @@ trait JavaScanners extends ast.parser.ScannersCommon {
       }
     }
 
-    protected def putCommentChar(): Unit = in.next()
+    // Hooks for ScaladocJavaUnitScanner
+    protected def beginDocComment(): Unit = {}
+    protected def processCommentChar(): Unit = {}
+    protected def finishDocComment(): Unit = {}
 
-    protected def skipBlockComment(isDoc: Boolean): Unit = in.ch match {
-      case SU  => incompleteInputError("unclosed comment")
-      case '*' => putCommentChar() ; if (in.ch == '/') putCommentChar() else skipBlockComment(isDoc)
-      case _   => putCommentChar() ; skipBlockComment(isDoc)
+    final protected def putCommentChar(): Unit = { processCommentChar(); in.next() }
+
+    @tailrec final protected def skipBlockComment(isDoc: Boolean): Unit = {
+      if (isDoc) beginDocComment()
+
+      in.ch match {
+        case SU  => incompleteInputError("unclosed comment")
+        case '*' => putCommentChar() ; if (in.ch == '/') putCommentChar() else skipBlockComment(isDoc)
+        case _   => putCommentChar() ; skipBlockComment(isDoc)
+      }
     }
 
-    protected def skipLineComment(): Unit = in.ch match {
+    @tailrec final protected def skipLineComment(): Unit = in.ch match {
       case CR | LF | SU =>
       case _            => putCommentChar() ; skipLineComment()
     }
 
-    protected def skipComment(): Boolean = in.ch match {
-      case '/' => putCommentChar() ; skipLineComment() ; true
+    final protected def skipComment(): Boolean = in.ch match {
+      case '/' => putCommentChar() ; skipLineComment() ; finishDocComment() ; true
       case '*' =>
         putCommentChar()
         in.ch match {
           case '*' => skipBlockComment(isDoc = true)
           case _ => skipBlockComment(isDoc = false)
         }
+        finishDocComment()
         true
       case _   => false
     }
diff --git a/src/scaladoc/scala/tools/nsc/doc/ScaladocAnalyzer.scala b/src/scaladoc/scala/tools/nsc/doc/ScaladocAnalyzer.scala
index d8ec7b18fd..f00af9a42f 100644
--- a/src/scaladoc/scala/tools/nsc/doc/ScaladocAnalyzer.scala
+++ b/src/scaladoc/scala/tools/nsc/doc/ScaladocAnalyzer.scala
@@ -215,51 +215,32 @@ abstract class ScaladocSyntaxAnalyzer[G <: Global](val global: G) extends Syntax
   }
 
   class ScaladocJavaUnitScanner(unit: CompilationUnit) extends JavaUnitScanner(unit) {
-
-    private var docBuffer: StringBuilder = _
-    private var inDocComment = false
+    // When `docBuffer == null`, we're not in a doc comment.
+    private var docBuffer: StringBuilder = null
     private var docStart: Int = 0
     private var lastDoc: DocComment = null
 
-    override def init() = {
-      docBuffer = new StringBuilder
-      super.init()
-    }
-
     // get last doc comment
     def flushDoc(): DocComment = try lastDoc finally lastDoc = null
 
-    override protected def putCommentChar(): Unit = {
-      if (inDocComment) docBuffer append in.ch
-      in.next
-    }
-
-    override protected def skipBlockComment(isDoc: Boolean): Unit = {
-      // condition is true when comment is entered the first time,
-      // i.e. immediately after "/*" and when current character is "*"
-      if (!inDocComment && isDoc) {
-        docBuffer append "/*"
+    override protected def beginDocComment(): Unit =
+      if (docBuffer == null) {
+        // Comment is entered the first time, i.e. immediately after "/*" and when current character is "*"
+        docBuffer = new StringBuilder("/*")
         docStart = currentPos.start
-        inDocComment = true
       }
-      super.skipBlockComment(isDoc)
-    }
 
-    override protected def skipComment(): Boolean = {
-      val skipped = super.skipComment()
-      if (skipped && inDocComment) {
+    override protected def processCommentChar(): Unit =
+      if (docBuffer != null) docBuffer append in.ch
+
+    override protected def finishDocComment(): Unit =
+      if (docBuffer != null) {
         val raw = docBuffer.toString
         val position = Position.range(unit.source, docStart, docStart, in.cpos)
         lastDoc = DocComment(raw, position)
         signalParsedDocComment(raw, position)
-        docBuffer.setLength(0) // clear buffer
-        inDocComment = false
-        true
-      } else {
-        skipped
+        docBuffer = null
       }
-    }
-
   }
 
   class ScaladocJavaUnitParser(unit: CompilationUnit) extends {
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