Group leaks by identified possible causes

[pyricau]

What matters when investigating leaks is not what we're leaking or what the gc root is, but what the possible causes are. Experience has shown that the same leak can lead to an activity, a fragment, or a view leaking. We can use the new reachability data to use the parts of the leak trace that are identified are possible cause as a grouping hash.

This is showing promising results internally at Square for remote reporting and grouping.

We should also group together all leaks excluded by the same exclusion.

[pyricau]

Also worth grouping compiled lambdas (which name change with each compile run). Need to build a list of examples:

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[pyricau]

We've got an interesting edge case when it comes to grouping: different parts of the hashmap implementation pointing to the same object lead to different leak traces. Leak Canary picks any of the shortests paths. Makes we wonder if we should sort those and pick the first, to have more consistent results and grouping.

[pyricau]

Need to update the UI to display leak groups first, then you open one group and see the group summary (ie subpart of leak trace) and a list of all instances and then you can dive in on any of those and you'll see a full leak trace.

[pyricau]

Also we will need to fix #1209

[pyricau]

• Update storage
  • The current heapdump and all analysis result are stored in the main app.
  • One root leakcanary directory
  • Stores only one heapdump, the heapdump in progress, deleted or moved immediately after analysis
  • In it, one folder for each analysis
  • In there, one file for each leaktrace. Each file has the hash of the trace causes as a prefix, which allows us to create groups with counts by just scanning the fs without reading any content. Still unclear: how do we represent such a group visually? We have counts that's all.aybe a tag for excluded leaks, not normal ones.

[pyricau]

This is done, although we need to polish the UI some more.