Raise a better exception with contextual information

Author: JMLF

src/OpalCompiler-Core/OCAbstractMethodScope.class.st

@@ -143,8 +143,11 @@ OCAbstractMethodScope >> localTemps [
 OCAbstractMethodScope >> lookupDefiningContextForVariable: var startingFrom: aContext [
 	"Is this the definition context for var? If it not, we look in the outer context using the corresponding outer scope. If found, we return the context"
 
+	| nextContext |
+	nextContext := self nextOuterScopeContextOf: aContext.
+	nextContext ifNil: [ self error: var name, ' optimized out' ].
 	^self = var scope
-		ifFalse: [ self outerScope lookupDefiningContextForVariable: var startingFrom: (self nextOuterScopeContextOf: aContext) ]
+		ifFalse: [ self outerScope lookupDefiningContextForVariable: var startingFrom: nextContext ]
 		ifTrue: [ aContext ]
 ]
 

src/OpalCompiler-Core/OCBlockScope.class.st

@@ -41,5 +41,5 @@ OCBlockScope >> nextOuterScopeContextOf: aContext [
 	"Returns the next context to lookup a variable name from within outer scope.
 	If it is block context then we return outer context for lookup.
 	But if it is method context lookup will continue in same context but within outer scope"
-	^ aContext outerContext ifNil: [ self error: 'OuterContext is not available' ]
+	^ aContext outerContext
 ]