Make ClassfileParser robust for directly reading Java inner classes

Usually when the ClassfileParser reads a classfile for a Java inner
class, the entry point is the outer class, the inner symbol is
created in `enterOwnInnerClasses`.

But when scanning the classpath, a Symbol is also created because
of the presence of the `C$I.class` classfile. (This symbol is later
unlinked and marked invalid.) When invoking the classfile parser on
this symbol directly, reading generic signatures can fail because
they may refer to type variables defined in the outer class:

```
class C1<X> {
  // signature: Lp/C1<TX;>; -- `TX;` references outer `X`
  class I extends C1<X> { }
}
```

Author: lrytz

src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala

@@ -627,6 +627,15 @@ abstract class ClassfileParser(reader: ReusableInstance[ReusableDataReader]) {
     }
   }
 
+  private class SigToTypeFail(msg: String) extends Throwable(msg)
+
+  // scala/bug#9152: sigToType can fail when directly accessing the symbol of a Java nested class
+  // `None` if `sig == null` or when `sigToType` fails
+  private def sigToTypeOpt(sym: Symbol, sig: String): Option[Type] = {
+    try Option(sig).map(sigToType(sym, _))
+    catch { case _: SigToTypeFail => None}
+  }
+
   private def sigToType(sym: Symbol, sig: String): Type = {
     val sigChars = sig.toCharArray
     var index = 0
@@ -749,7 +758,7 @@ abstract class ClassfileParser(reader: ReusableInstance[ReusableDataReader]) {
           val n = newTypeName(subName(';'.==))
           index += 1
           if (skiptvs) AnyTpe
-          else tparams(n).typeConstructor
+          else tparams.getOrElse(n, throw new SigToTypeFail(s"unknown type variable: $n")).typeConstructor
       }
     } // sig2type(tparams, skiptvs)
 
@@ -1295,7 +1304,7 @@ abstract class ClassfileParser(reader: ReusableInstance[ReusableDataReader]) {
   private final class ClassTypeCompleter(@unused name: Name, @unused jflags: JavaAccFlags, parent: NameOrString, ifaces: List[NameOrString]) extends JavaTypeCompleter {
     var permittedSubclasses: List[symbolTable.Symbol] = Nil
     override def complete(sym: symbolTable.Symbol): Unit = {
-      val info = if (sig != null) sigToType(sym, sig) else {
+      val info = sigToTypeOpt(sym, sig).getOrElse {
         val superTpe = if (parent == null) definitions.AnyClass.tpe_* else getClassSymbol(parent.value).tpe_*
         val superTpe1 = if (superTpe == ObjectTpeJava) ObjectTpe else superTpe
         val ifacesTypes = ifaces.filterNot(_ eq null).map(x => getClassSymbol(x.value).tpe_*)
@@ -1335,25 +1344,25 @@ abstract class ClassfileParser(reader: ReusableInstance[ReusableDataReader]) {
         case _ => false
       })
 
-      val info = if (sig != null) {
-        sigToType(sym, sig)
-      } else if (name == nme.CONSTRUCTOR) {
-        descriptorInfo match {
-          case MethodType(params, _) =>
-            val paramsNoOuter = if (hasOuterParam) params.tail else params
-            val newParams = paramsNoOuter match {
-              case init :+ _ if jflags.isSynthetic =>
-                // scala/bug#7455 strip trailing dummy argument ("access constructor tag") from synthetic constructors which
-                // are added when an inner class needs to access a private constructor.
-                init
-              case _ =>
-                paramsNoOuter
-            }
-            MethodType(newParams, clazz.tpe)
-          case info => info
+      val info = sigToTypeOpt(sym, sig).getOrElse {
+        if (name == nme.CONSTRUCTOR) {
+          descriptorInfo match {
+            case MethodType(params, _) =>
+              val paramsNoOuter = if (hasOuterParam) params.tail else params
+              val newParams = paramsNoOuter match {
+                case init :+ _ if jflags.isSynthetic =>
+                  // scala/bug#7455 strip trailing dummy argument ("access constructor tag") from synthetic constructors which
+                  // are added when an inner class needs to access a private constructor.
+                  init
+                case _ =>
+                  paramsNoOuter
+              }
+              MethodType(newParams, clazz.tpe)
+            case info => info
+          }
+        } else {
+          descriptorInfo
         }
-      } else {
-        descriptorInfo
       }
       if (constant != null) {
         val c1 = convertTo(constant, info.resultType)

test/files/run/t9152.check

@@ -0,0 +1,42 @@
+
+scala> :power
+Power mode enabled. :phase is at typer.
+import scala.tools.nsc._, intp.global._, definitions._
+Try :help or completions for vals._ and power._
+
+scala> import rootMirror._
+import rootMirror._
+
+scala> getClassIfDefined("p.C1$I").info
+val res0: $r.intp.global.Type =
+p.C1 {
+  private[package p] def <init>(): p.C1$I
+}
+
+scala> getClassIfDefined("p.C2$I").info
+val res1: $r.intp.global.Type =
+Object {
+  private[package p] def <init>(): p.C2$I
+  private[package p] def foo(): p.C2[_]
+}
+
+scala> getClassIfDefined("p.C1$I") // symbol unlinked after reading C1
+val res2: $r.intp.global.Symbol = <none>
+
+scala> getClassIfDefined("p.C2$I") // symbol unlinked after reading C2
+val res3: $r.intp.global.Symbol = <none>
+
+scala> getClassIfDefined("p.C1").info.member(TypeName("I")).info
+val res4: $r.intp.global.Type =
+p.C1[X] {
+  private[package p] def <init>(): C1.this.I
+}
+
+scala> getClassIfDefined("p.C2").info.member(TypeName("I")).info
+val res5: $r.intp.global.Type =
+Object {
+  private[package p] def <init>(): C2.this.I
+  private[package p] def foo(): p.C2[X]
+}
+
+scala> :quit

test/files/run/t9152/C_1.java

@@ -0,0 +1,11 @@
+package p;
+
+class C1<X> {
+  class I extends C1<X> { }
+}
+
+class C2<X> {
+  class I {
+    C2<X> foo() { return null; }
+  }
+}

test/files/run/t9152/Test.scala

@@ -0,0 +1,14 @@
+import scala.tools.partest.ReplTest
+
+object Test extends ReplTest {
+  def code = """
+    |:power
+    |import rootMirror._
+    |getClassIfDefined("p.C1$I").info
+    |getClassIfDefined("p.C2$I").info
+    |getClassIfDefined("p.C1$I") // symbol unlinked after reading C1
+    |getClassIfDefined("p.C2$I") // symbol unlinked after reading C2
+    |getClassIfDefined("p.C1").info.member(TypeName("I")).info
+    |getClassIfDefined("p.C2").info.member(TypeName("I")).info
+  """.stripMargin
+}