Closes SI-5821.

This was an interesting one. Basically an erroneous
import was creating an erroneous symbol for Array (similary
for other symbols that were 'found' in this import) which was
leading to all sorts of inconsistencies and spurious errors.

This wasn't a bug in ContextErrors but rather something that
existed for ages and was hidden from the general audience.

Review by @paulp.

6 files changed, 35 insertions, 11 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Namers.scala b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
index 2f2278251b..8952012d6c 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Namers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
@@ -1306,14 +1306,18 @@ trait Namers extends MethodSynthesis {
           if (expr1.symbol != null && expr1.symbol.isRootPackage)
             RootImportError(tree)
 
-          val newImport = treeCopy.Import(tree, expr1, selectors).asInstanceOf[Import]
-          checkSelectors(newImport)
-          transformed(tree) = newImport
-          // copy symbol and type attributes back into old expression
-          // so that the structure builder will find it.
-          expr.symbol = expr1.symbol
-          expr.tpe = expr1.tpe
-          ImportType(expr1)
+          if (expr1.isErrorTyped)
+            ErrorType
+          else {
+            val newImport = treeCopy.Import(tree, expr1, selectors).asInstanceOf[Import]
+            checkSelectors(newImport)
+            transformed(tree) = newImport
+            // copy symbol and type attributes back into old expression
+            // so that the structure builder will find it.
+            expr.symbol = expr1.symbol
+            expr.tpe = expr1.tpe
+            ImportType(expr1)
+          }
       }
 
       val result =
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index e40a567f1d..fb970bc84a 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -2552,9 +2552,11 @@ trait Typers extends Modes with Adaptations with Taggings {
         else
           stat match {
             case imp @ Import(_, _) =>
-              context = context.makeNewImport(imp)
               imp.symbol.initialize
-              typedImport(imp)
+              if (!imp.symbol.isError) {
+                context = context.makeNewImport(imp)
+                typedImport(imp)
+              } else EmptyTree
             case _ =>
               if (localTarget && !includesTargetPos(stat)) {
                 // skip typechecking of statements in a sequence where some other statement includes
diff --git a/test/files/buildmanager/t2792/t2792.check b/test/files/buildmanager/t2792/t2792.check
index 68e14c6386..00a2b83469 100644
--- a/test/files/buildmanager/t2792/t2792.check
+++ b/test/files/buildmanager/t2792/t2792.check
@@ -9,3 +9,6 @@ compiling Set(A2.scala)
 A2.scala:2: error: stable identifier required, but A.x found.
   import A.x.y
            ^
+A2.scala:3: error: not found: value y
+  val z = y
+          ^
diff --git a/test/files/neg/t5821.check b/test/files/neg/t5821.check
new file mode 100644
index 0000000000..f9c00604bc
--- /dev/null
+++ b/test/files/neg/t5821.check
@@ -0,0 +1,4 @@
+t5821.scala:1: error: not found: object SthImportant
+import SthImportant._
+       ^
+one error found
diff --git a/test/files/neg/t5821.scala b/test/files/neg/t5821.scala
new file mode 100644
index 0000000000..4af0a2bf7f
--- /dev/null
+++ b/test/files/neg/t5821.scala
@@ -0,0 +1,8 @@
+import SthImportant._
+
+class Bar
+
+class Foo2 {
+  type Sth = Array[Bar]
+  def foo(xs: Sth): Bar = if ((xs eq null) || (xs.length == 0)) null else xs(0)
+}
diff --git a/test/files/neg/t639.check b/test/files/neg/t639.check
index 3b53da0515..6d41d872de 100644
--- a/test/files/neg/t639.check
+++ b/test/files/neg/t639.check
@@ -1,4 +1,7 @@
 t639.scala:3: error: not found: object a
 import a._
        ^
-one error found
+t639.scala:5: error: not found: type B
+@B
+ ^
+two errors found