stack overflow using #inline anchor

I am making my own TextMorph (subclass) in which I want to be able to
drag any Morph embedded directly into the text.

TextMorph already supports this via #anchorMorph:at:type:.  I am
interested in providing an enriched #inline embedding.

What I've done in MyTextMorph is express interest in mouse-over
dragging by overriding #mouseEnterDragging: and #mouseLeaveDragging:
which #startTrackingDropZones and #stopTrackingDropZones,
respectively.

Tracking drop zones is nothing more than stepping real fast to show a
"marker" morph by calling the above mentioned method:

        ...
        self
                anchorMorph: spacer
                at: hand position
                type: #inline

It works great!  Except.. *sometimes*, when being rough with it,
shaking a big morph around in the text it gets into an infinite
recursion (sans stack overflow error), which I've pasted at the end of
this message.

There is a guard in CompositionScanner>>#placeEmbeddedObject: anchoredMorph
        | descent |
        "Workaround: The following should really use #textAnchorType"
        anchoredMorph relativeTextAnchorPosition ifNotNil:[^true].

which piqued my interest because of the comment,

and another in TextAnchor>>#emphasizeScanner: aScanner
        self anchoredMorph ifNil: [ ^ self ].
        aScanner placeEmbeddedObject: self anchoredMorph.

which is interesting because of the fact it is related to its #anchoredMorph.

Unfortunately, an infiinite recursion is a bad show-stopper, I need
advice to help find an appropriate guard to prevent the recursion.

Any help is much appreciated.

 - Chris



From: chris
To: [hidden email]
Subject: [BUG]IdentityDictionary(Dictionary)>>at:ifAbsent:

here insert explanation of what you were doing, suspect changes you've
made and so forth.

4 October 2007 12:41:17 am

VM: Win32 - a SmalltalkImage
Image: Squeak3.9 [latest update: #7067]

SecurityManager state:
Restricted: false
FileAccess: true
SocketAccess: true

IdentityDictionary(Dictionary)>>at:ifAbsent:
        Receiver: an IdentityDictionary()
        Arguments and temporary variables:
                key: #relativeTextAnchorPosition
                aBlock: [] in MorphExtension>>valueOfProperty:ifAbsent: {[^ aBlock value]}
                assoc: nil
        Receiver's instance variables:
                tally: 0
                array: #(nil nil nil nil nil)

MorphExtension>>valueOfProperty:ifAbsent:
        Receiver: a MorphExtension (602)
        Arguments and temporary variables:
                aSymbol: #relativeTextAnchorPosition
                aBlock: [] in MorphExtension>>valueOfProperty: {[]}
        Receiver's instance variables:
                locked: false
                visible: true
                sticky: false
                balloonText: nil
                balloonTextSelector: nil
                externalName: nil
                isPartsDonor: false
                actorState: nil
                player: nil
                eventHandler: nil
                otherProperties: nil

MorphExtension>>valueOfProperty:
        Receiver: a MorphExtension (602)
        Arguments and temporary variables:
                aSymbol: #relativeTextAnchorPosition
        Receiver's instance variables:
                locked: false
                visible: true
                sticky: false
                balloonText: nil
                balloonTextSelector: nil
                externalName: nil
                isPartsDonor: false
                actorState: nil
                player: nil
                eventHandler: nil
                otherProperties: nil

RectangleMorph(Morph)>>valueOfProperty:
        Receiver: a RectangleMorph(749)
        Arguments and temporary variables:
                aSymbol: #relativeTextAnchorPosition
        Receiver's instance variables:
                bounds: 0@0 corner: 94@142
                owner: nil
                submorphs: #()
                fullBounds: 0@0 corner: 94@142
                color: Color transparent
                extension: a MorphExtension (602)
                borderWidth: 1
                borderColor: Color green


--- The full stack ---
IdentityDictionary(Dictionary)>>at:ifAbsent:
MorphExtension>>valueOfProperty:ifAbsent:
MorphExtension>>valueOfProperty:
RectangleMorph(Morph)>>valueOfProperty:
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
RectangleMorph(Morph)>>relativeTextAnchorPosition
CompositionScanner>>placeEmbeddedObject:
TextAnchor>>emphasizeScanner:
[] in CompositionScanner(CharacterScanner)>>setFont {[:att | att
emphasizeScanner: self]}
Array(SequenceableCollection)>>do:
CompositionScanner(CharacterScanner)>>setFont
CompositionScanner>>setFont
CompositionScanner(CharacterScanner)>>placeEmbeddedObject:
CompositionScanner>>placeEmbeddedObject:
TextAnchor>>emphasizeScanner:
[] in CompositionScanner(CharacterScanner)>>setFont {[:att | att
emphasizeScanner: self]}
Array(SequenceableCollection)>>do:
CompositionScanner(CharacterScanner)>>setFont
CompositionScanner>>setFont
CompositionScanner(CharacterScanner)>>placeEmbeddedObject:
CompositionScanner>>placeEmbeddedObject:
TextAnchor>>emphasizeScanner:
[] in CompositionScanner(CharacterScanner)>>setFont {[:att | att
emphasizeScanner: self]}
Array(SequenceableCollection)>>do:
CompositionScanner(CharacterScanner)>>setFont
CompositionScanner>>setFont
CompositionScanner(CharacterScanner)>>placeEmbeddedObject:
CompositionScanner>>placeEmbeddedObject:
TextAnchor>>emphasizeScanner:
[] in CompositionScanner(CharacterScanner)>>setFont {[:att | att
emphasizeScanner: self]}
Array(SequenceableCollection)>>do:
CompositionScanner(CharacterScanner)>>setFont
CompositionScanner>>setFont
CompositionScanner(CharacterScanner)>>placeEmbeddedObject:
CompositionScanner>>placeEmbeddedObject:
TextAnchor>>emphasizeScanner:
[] in CompositionScanner(CharacterScanner)>>setFont {[:att | att
emphasizeScanner: self]}
Array(SequenceableCollection)>>do:
CompositionScanner(CharacterScanner)>>setFont
CompositionScanner>>setFont
CompositionScanner(CharacterScanner)>>placeEmbeddedObject:
CompositionScanner>>placeEmbeddedObject:
TextAnchor>>emphasizeScanner:
[] in CompositionScanner(CharacterScanner)>>setFont {[:att | att
emphasizeScanner: self]}
Array(SequenceableCollection)>>do:
CompositionScanner(CharacterScanner)>>setFont
CompositionScanner>>setFont
CompositionScanner(CharacterScanner)>>placeEmbeddedObject:
CompositionScanner>>placeEmbeddedObject:
TextAnchor>>emphasizeScanner:
[] in CompositionScanner(CharacterScanner)>>setFont {[:att | att
emphasizeScanner: self]}
...etc...