SI-8888 Avoid ClassFormatError under -Ydelambdafy:method

retronym · retronym · commit 1ee6352a79d0 · 2014-10-07T15:09:28.000+10:00
The pattern matcher phase (conceivably, among others) can generate
code that binds local `Ident`s symbolically, rather than according
to the lexical scope. This means that a lambda can capture more than
one local of the same name.

In the enclosed test case, this ends up creating the following
tree after delambdafy

    [[syntax trees at end of                delambdafy]] // delambday-patmat-path-dep.scala
    matchEnd4({
      case &lt;synthetic&gt; val x1: Object = (x2: Object);
      case5(){
        if (x1.$isInstanceOf[C]())
          {
            &lt;synthetic&gt; val x2#19598: C = (x1.$asInstanceOf[C](): C);
            matchEnd4({
              {
                (new resume$1(x2#19598, x2#19639): runtime.AbstractFunction0)
              };
              scala.runtime.BoxedUnit.UNIT
            })
          }
        else
          case6()
      };
      ...
    })
    ...
    &lt;synthetic&gt; class resume$1 extends AbstractFunction0 {
      &lt;synthetic&gt; var x2: C = null;
      &lt;synthetic&gt; var x2: C = null;
      ...
    }

After this commit, the var members of `resume$1` are given fresh
names, rather than directly using the name of the captured var:

    &lt;synthetic&gt; var x2$3: C = null;
    &lt;synthetic&gt; var x2$4: C = null;
diff --git a/src/compiler/scala/tools/nsc/transform/Delambdafy.scala b/src/compiler/scala/tools/nsc/transform/Delambdafy.scala
@@ -260,7 +260,7 @@ abstract class Delambdafy extends Transform with TypingTransformers with ast.Tre
 
         val captureProxies2 = new LinkedHashMap[Symbol, TermSymbol]
         captures foreach {capture =>
-          val sym = lambdaClass.newVariable(capture.name.toTermName, capture.pos, SYNTHETIC)
+          val sym = lambdaClass.newVariable(unit.freshTermName(capture.name.toString + "$"), capture.pos, SYNTHETIC)
           sym setInfo capture.info
           captureProxies2 += ((capture, sym))
         }
diff --git a/test/files/run/t8888.flags b/test/files/run/t8888.flags
@@ -0,0 +1 @@
+-Ydelambdafy:method
diff --git a/test/files/run/t8888.scala b/test/files/run/t8888.scala
@@ -0,0 +1,12 @@
+class C {
+  final def resume: Unit = (this: Any) match {
+    case x : C => (x: Any) match {
+      case y : C =>
+        () => (x, y) // used to trigger a ClassFormatError under -Ydelambdafy:method
+    }
+  }
+}
+
+object Test extends App {
+  new C().resume
+}

Original file line number	Diff line number	Diff line change
`@@ -260,7 +260,7 @@ abstract class Delambdafy extends Transform with TypingTransformers with ast.Tre`
`260`	`260`
`261`	`261`	`val captureProxies2 = new LinkedHashMap[Symbol, TermSymbol]`
`262`	`262`	`captures foreach {capture =>`
`263`		`- val sym = lambdaClass.newVariable(capture.name.toTermName, capture.pos, SYNTHETIC)`
	`263`	`+ val sym = lambdaClass.newVariable(unit.freshTermName(capture.name.toString + "$"), capture.pos, SYNTHETIC)`
`264`	`264`	`sym setInfo capture.info`
`265`	`265`	`captureProxies2 += ((capture, sym))`
`266`	`266`	`}`