SI-10066 Fix crash in erroneous code with implicits, dynamic

The compiler support in the typechecker for `scala.Dynamic` is
very particular about the `Context` in which it is typechecked.
It looks at the `tree` in the enclosing context to find the expression
immediately enclosing the dynamic selection. See the logic in
`dyna::mkInvoke` for the details.

This commit substitutes the result of `resetAttrs` into the tree
of the typer context before continuing with typechecking.

3 files changed, 83 insertions, 0 deletions

diff --git a/test/files/neg/t10066.check b/test/files/neg/t10066.check
new file mode 100644
index 0000000000..3555205d83
--- /dev/null
+++ b/test/files/neg/t10066.check
@@ -0,0 +1,7 @@
+t10066.scala:33: error: could not find implicit value for parameter extractor: dynamicrash.Extractor[String]
+  println(storage.foo[String])
+          ^
+t10066.scala:37: error: could not find implicit value for parameter extractor: dynamicrash.Extractor[A]
+  println(storage.foo)
+          ^
+two errors found
diff --git a/test/files/neg/t10066.scala b/test/files/neg/t10066.scala
new file mode 100644
index 0000000000..ef52f333dd
--- /dev/null
+++ b/test/files/neg/t10066.scala
@@ -0,0 +1,38 @@
+package dynamicrash
+
+import scala.language.dynamics
+
+class Config
+
+trait Extractor[A] {
+  def extract(config: Config, name: String): A
+}
+
+object Extractor {
+  // note missing "implicit"
+  val stringExtractor = new Extractor[String] {
+    override def extract(config: Config, name: String): String = ???
+  }
+}
+
+class Workspace extends Dynamic {
+  val config: Config = new Config
+
+  def selectDynamic[A](name: String)(implicit extractor: Extractor[A]): A =
+    extractor.extract(config, name)
+}
+
+object Main {
+  val storage = new Workspace
+
+  // this line works fine
+  // val a = storage.foo
+
+  // this line crashes the compiler ("head of empty list")
+  // in ContextErrors$InferencerContextErrors$InferErrorGen$.NotWithinBoundsErrorMessage
+  println(storage.foo[String])
+
+  // this line crashes the compiler in different way ("unknown type")
+  // in the backend, warning: an unexpected type representation reached the compiler backend while compiling Test.scala: <error>
+  println(storage.foo)
+}
diff --git a/test/files/pos/t10066.scala b/test/files/pos/t10066.scala
new file mode 100644
index 0000000000..bef85cb08c
--- /dev/null
+++ b/test/files/pos/t10066.scala
@@ -0,0 +1,38 @@
+package dynamicrash
+ 
+import scala.language.dynamics
+ 
+class Config
+ 
+trait Extractor[A] {
+  def extract(config: Config, name: String): A
+}
+ 
+object Extractor {
+  // this has "implicit", unlike the corresponding neg test
+  implicit val stringExtractor = new Extractor[String] {
+    override def extract(config: Config, name: String): String = ???
+  }
+}
+ 
+class Workspace extends Dynamic {
+  val config: Config = new Config
+ 
+  def selectDynamic[A](name: String)(implicit extractor: Extractor[A]): A =
+    extractor.extract(config, name)
+}
+ 
+object Main {
+  val storage = new Workspace
+ 
+  // this line works fine
+  // val a = storage.foo
+ 
+  // this line crashes the compiler ("head of empty list")
+  // in ContextErrors$InferencerContextErrors$InferErrorGen$.NotWithinBoundsErrorMessage
+  println(storage.foo[String])
+ 
+  // this line crashes the compiler in different way ("unknown type")
+  // in the backend, warning: an unexpected type representation reached the compiler backend while compiling Test.scala: <error>
+  println(storage.foo)
+}