Fix #7758: Avoid stackoverflows after inline attempts

Author: odersky

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -314,7 +314,7 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
     // Precondition: !isSubType(tp1, tp2) && !isSubType(tp2, tp1).
     if (!ctx.explicitNulls && (tp1.isNullType || tp2.isNullType)) {
       // Since projections of types don't include null, intersection with null is empty.
-      return Empty
+      Empty
     }
     else {
       val res = ctx.typeComparer.provablyDisjoint(tp1, tp2)

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -2826,7 +2826,8 @@ class Typer extends Namer
         tree.tpe <:< wildApprox(pt)
         val errorCount = ctx.reporter.errorCount
         val inlined = Inliner.inlineCall(tree)
-        if (errorCount == ctx.reporter.errorCount) readaptSimplified(inlined) else inlined
+        if ((inlined ne tree) && errorCount == ctx.reporter.errorCount) readaptSimplified(inlined)
+        else inlined
       }
       else if (tree.symbol.isScala2Macro &&
                // raw and s are eliminated by the StringInterpolatorOpt phase

tests/neg/i7758.scala

@@ -0,0 +1 @@
+def f: Int = implicitly: Int