closes #742.

review by extempore

3 files changed, 24 insertions, 15 deletions

diff --git a/src/compiler/scala/tools/nsc/symtab/Types.scala b/src/compiler/scala/tools/nsc/symtab/Types.scala
index 15c5fb6c0e..9e10d3a408 100644
--- a/src/compiler/scala/tools/nsc/symtab/Types.scala
+++ b/src/compiler/scala/tools/nsc/symtab/Types.scala
@@ -394,9 +394,10 @@ trait Types extends reflect.generic.Types { self: SymbolTable =>
 
     /** Replace formal type parameter symbols with actual type arguments.
      *
-     * Amounts to substitution except for higher-kinded types. (See overridden method in TypeRef) -- @M (contact adriaan.moors at cs.kuleuven.be)
+     * Amounts to substitution except for higher-kinded types. (See overridden method in TypeRef) -- @M
      */
-    def instantiateTypeParams(formals: List[Symbol], actuals: List[Type]): Type = this.subst(formals, actuals)
+    def instantiateTypeParams(formals: List[Symbol], actuals: List[Type]): Type =
+      if(formals.length == actuals.length) this.subst(formals, actuals) else ErrorType
 
     /** If this type is an existential, turn all existentially bound variables to type skolems.
      *  @param  owner    The owner of the created type skolems
@@ -1706,8 +1707,9 @@ A type's typeSymbol should never be inspected directly.
 
         if (substTps.length == typeParams.length)
           typeRef(pre, sym, actuals)
-        else // partial application (needed in infer when bunching type arguments from classes and methods together)
+        else if(formals.length == actuals.length) // partial application (needed in infer when bunching type arguments from classes and methods together)
           typeRef(pre, sym, dummyArgs).subst(formals, actuals)
+        else ErrorType
       }
       else
         super.instantiateTypeParams(formals, actuals)
@@ -1726,21 +1728,15 @@ A type's typeSymbol should never be inspected directly.
       if (sym == clazz && !args.isEmpty) args.head else this
 
     def normalize0: Type =
-      if (sym.isAliasType) { // beta-reduce
-        if (sym.info.typeParams.length == args.length || !isHigherKinded) {
-          /* !isHigherKinded && sym.info.typeParams.length != args.length only happens when compiling e.g.,
-           `val x: Class' with -Xgenerics, while `type Class = java.lang.Class' had already been compiled without -Xgenerics */
-          val xform = transform(sym.info.resultType)
-          assert(xform ne this, this)
-          xform.normalize // cycles have been checked in typeRef
-        } else { // should rarely happen, if at all
-          PolyType(sym.info.typeParams, transform(sym.info.resultType).normalize)  // eta-expand -- for regularity, go through sym.info for typeParams
-          // @M TODO: should not use PolyType, as that's the type of a polymorphic value -- we really want a type *function*
-        }
-      } else if (isHigherKinded) {
+      if (isHigherKinded) {
         // @M TODO: should not use PolyType, as that's the type of a polymorphic value -- we really want a type *function*
         // @M: initialize (by sym.info call) needed (see test/files/pos/ticket0137.scala)
         PolyType(sym.info.typeParams, typeRef(pre, sym, dummyArgs)) // must go through sym.info for typeParams
+      } else if (sym.isAliasType) { // beta-reduce
+        if(sym.info.typeParams.length == args.length) // don't do partial application
+          transform(sym.info.resultType).normalize // cycles have been checked in typeRef
+        else
+          ErrorType
       } else if (sym.isRefinementClass) {
         sym.info.normalize // @MO to AM: OK?
         //@M I think this is okay, but changeset 12414 (which fixed #1241) re-introduced another bug (#2208)
diff --git a/test/files/neg/t742.check b/test/files/neg/t742.check
new file mode 100644
index 0000000000..f587948ef1
--- /dev/null
+++ b/test/files/neg/t742.check
@@ -0,0 +1,5 @@
+t742.scala:5: error: kinds of the type arguments (Crash._1,Crash._2,Any) do not conform to the expected kinds of the type parameters (type m,type n,type z).
+Crash._1's type parameters do not match type m's expected parameters: type s1 has one type parameter, but type n has two
+    type p = mul[_1, _2, Any]  // mul[_1, _1, Any] needs -Yrecursion
+             ^
+one error found
diff --git a/test/files/neg/t742.scala b/test/files/neg/t742.scala
new file mode 100644
index 0000000000..bb1c2f85ea
--- /dev/null
+++ b/test/files/neg/t742.scala
@@ -0,0 +1,8 @@
+object Crash {
+    type mul[m[n[s[_], z], z], n[s[_], z], z] = m[n, z]
+    type _1[s1[_], z1] = s1[z1]
+    type _2[s1[_], z1] = s1[z1]
+    type p = mul[_1, _2, Any]  // mul[_1, _1, Any] needs -Yrecursion
+    // _1[_2, Zero]
+    // _2[Zero]
+}
\ No newline at end of file