From 4efe998b76fa471c04c15e1a4f05ab858be8deb8 Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Thu, 15 Feb 2018 14:58:01 +0100
Subject: [PATCH 1/2] Harden IDE: Catch NoSuchFileException

A NoSuchFileException was observed for a non-existing directory on the classpath:

    /Users/odersky/workspace/dotty/compiler/../out/bootstrap/dotty-compiler-bootstrapped/scala-0.7/classes

It was after a dotty-bootstrapped/clean. I believe this should be ignored, or maybe handled with
an error message. But certainly not a crash.
---
 .../dotc/interactive/InteractiveDriver.scala  | 28 +++++++++++--------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/interactive/InteractiveDriver.scala b/compiler/src/dotty/tools/dotc/interactive/InteractiveDriver.scala
index 3940547ffa81..8d2b0f434c64 100644
--- a/compiler/src/dotty/tools/dotc/interactive/InteractiveDriver.scala
+++ b/compiler/src/dotty/tools/dotc/interactive/InteractiveDriver.scala
@@ -148,20 +148,24 @@ class InteractiveDriver(settings: List[String]) extends Driver {
     val names = new mutable.ListBuffer[String]
     dirClassPaths.foreach { dirCp =>
       val root = dirCp.dir.toPath
-      Files.walkFileTree(root, new SimpleFileVisitor[Path] {
-        override def visitFile(path: Path, attrs: BasicFileAttributes) = {
-          if (!attrs.isDirectory) {
-            val name = path.getFileName.toString
-            for {
-              tastySuffix <- tastySuffixes
-              if name.endsWith(tastySuffix)
-            } {
-              names += root.relativize(path).toString.replace("/", ".").stripSuffix(tastySuffix)
+      try
+        Files.walkFileTree(root, new SimpleFileVisitor[Path] {
+          override def visitFile(path: Path, attrs: BasicFileAttributes) = {
+            if (!attrs.isDirectory) {
+              val name = path.getFileName.toString
+              for {
+                tastySuffix <- tastySuffixes
+                if name.endsWith(tastySuffix)
+              } {
+                names += root.relativize(path).toString.replace("/", ".").stripSuffix(tastySuffix)
+              }
             }
+            FileVisitResult.CONTINUE
           }
-          FileVisitResult.CONTINUE
-        }
-      })
+        })
+      catch {
+        case _: NoSuchFileException =>
+      }
     }
     names.toList
   }

From 86c762079b86b1c0f18493edb2ce59b96a470eee Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Sat, 17 Feb 2018 18:37:44 +0100
Subject: [PATCH 2/2] Make pathTo operation more robust

Paths can contain non-tree elements. I observed a path that contained
an untpd.Mod instead of a tree.

Also, we should survive possible cyclic references when ccomputing the context
of a path. (this was also observed in the wild but I can't reproduce it).
---
 .../src/dotty/tools/dotc/interactive/Interactive.scala     | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/interactive/Interactive.scala b/compiler/src/dotty/tools/dotc/interactive/Interactive.scala
index e884429b97cd..0e1456764088 100644
--- a/compiler/src/dotty/tools/dotc/interactive/Interactive.scala
+++ b/compiler/src/dotty/tools/dotc/interactive/Interactive.scala
@@ -344,7 +344,7 @@ object Interactive {
     if (tree.pos.contains(pos)) {
       // FIXME: We shouldn't need a cast. Change NavigateAST.pathTo to return a List of Tree?
       val path = NavigateAST.pathTo(pos, tree, skipZeroExtent = true).asInstanceOf[List[untpd.Tree]]
-      path.dropWhile(!_.hasType).asInstanceOf[List[tpd.Tree]]
+      path.dropWhile(!_.hasType) collect { case t: tpd.Tree @unchecked => t }
     }
     else Nil
 
@@ -365,7 +365,7 @@ object Interactive {
     case nested :: encl :: rest =>
       import typer.Typer._
       val outer = contextOfPath(encl :: rest)
-      encl match {
+      try encl match {
         case tree @ PackageDef(pkg, stats) =>
           assert(tree.symbol.exists)
           if (nested `eq` pkg) outer
@@ -401,6 +401,9 @@ object Interactive {
         case _ =>
           outer
       }
+      catch {
+        case ex: CyclicReference => outer
+      }
   }
 
   /** The first tree in the path that is a definition. */