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author | Eugene Burmako <xeno.by@gmail.com> | 2013-02-23 13:40:14 +0100 |
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committer | Eugene Burmako <xeno.by@gmail.com> | 2013-05-12 22:19:02 +0200 |
commit | c539ae2f56fe9f565cffb4afd6ab131bda89acb7 (patch) | |
tree | 30c9472e80b9732b713ab0efa0c148827808276f /src/compiler/scala/tools/nsc/typechecker/Implicits.scala | |
parent | a35b6bc8e4369db8983d6d0d9881f37d7affbadd (diff) | |
download | scala-c539ae2f56fe9f565cffb4afd6ab131bda89acb7.tar.gz scala-c539ae2f56fe9f565cffb4afd6ab131bda89acb7.tar.bz2 scala-c539ae2f56fe9f565cffb4afd6ab131bda89acb7.zip |
SI-7167 implicit macros decide what is divergence
This is a port of https://github.com/scala/scala/commit/8168f118c9 from 2.10.x,
with an additional change to the `enclosingImplicits` and `openImplicits` APIs,
which encapsulates tuples of `pt` and `tree` into `ImplicitCandidate`.
Diffstat (limited to 'src/compiler/scala/tools/nsc/typechecker/Implicits.scala')
-rw-r--r-- | src/compiler/scala/tools/nsc/typechecker/Implicits.scala | 20 |
1 files changed, 18 insertions, 2 deletions
diff --git a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala index f27c15180e..6b8c01b0a2 100644 --- a/src/compiler/scala/tools/nsc/typechecker/Implicits.scala +++ b/src/compiler/scala/tools/nsc/typechecker/Implicits.scala @@ -224,6 +224,10 @@ trait Implicits { ) } + /** A class which is used to track pending implicits to prevent infinite implicit searches. + */ + case class OpenImplicit(info: ImplicitInfo, pt: Type, tree: Tree) + /** A sentinel indicating no implicit was found */ val NoImplicitInfo = new ImplicitInfo(null, NoType, NoSymbol) { // equals used to be implemented in ImplicitInfo with an `if(this eq NoImplicitInfo)` @@ -407,13 +411,25 @@ trait Implicits { * @pre `info.tpe` does not contain an error */ private def typedImplicit(info: ImplicitInfo, ptChecked: Boolean, isLocal: Boolean): SearchResult = { - (context.openImplicits find { case (tp, tree1) => tree1.symbol == tree.symbol && dominates(pt, tp)}) match { + // SI-7167 let implicit macros decide what amounts for a divergent implicit search + // imagine a macro writer which wants to synthesize a complex implicit Complex[T] by making recursive calls to Complex[U] for its parts + // e.g. we have `class Foo(val bar: Bar)` and `class Bar(val x: Int)` + // then it's quite reasonable for the macro writer to synthesize Complex[Foo] by calling `inferImplicitValue(typeOf[Complex[Bar])` + // however if we didn't insert the `info.sym.isMacro` check here, then under some circumstances + // (e.g. as described here http://groups.google.com/group/scala-internals/browse_thread/thread/545462b377b0ac0a) + // `dominates` might decide that `Bar` dominates `Foo` and therefore a recursive implicit search should be prohibited + // now when we yield control of divergent expansions to the macro writer, what happens next? + // in the worst case, if the macro writer is careless, we'll get a StackOverflowException from repeated macro calls + // otherwise, the macro writer could check `c.openMacros` and `c.openImplicits` and do `c.abort` when expansions are deemed to be divergent + // upon receiving `c.abort` the typechecker will decide that the corresponding implicit search has failed + // which will fail the entire stack of implicit searches, producing a nice error message provided by the programmer + (context.openImplicits find { case OpenImplicit(info, tp, tree1) => !info.sym.isMacro && tree1.symbol == tree.symbol && dominates(pt, tp)}) match { case Some(pending) => //println("Pending implicit "+pending+" dominates "+pt+"/"+undetParams) //@MDEBUG DivergentSearchFailure case None => try { - context.openImplicits = (pt, tree) :: context.openImplicits + context.openImplicits = OpenImplicit(info, pt, tree) :: context.openImplicits // println(" "*context.openImplicits.length+"typed implicit "+info+" for "+pt) //@MDEBUG val result = typedImplicit0(info, ptChecked, isLocal) if (result.isDivergent) { |