RevDiff: FirstRevision is null for the initial commit

[gerhardol]

Fixes #8085

Proposed changes

• Refactor: Align FirstParentId name
  Guid suffix is quite consistently used for the string representation of the hash, while Id suffix is used for ObjectId, this was therefore switched
  Some parentGuids changed too, not changing treeGuid

• Use "--root" for first revision if null
  Handle GitRevision == null as the root commit, before the initial commit, i.e. compare to /dev/null
  SemanticMerge and KDiff3 shows such a diff, Tortoise does not for some reason
  (The alternative would be to not add null to the revisions to diff which will result in a argument popup which is OK to me.)

• RevDiff: FirstRevision is null for the initial commit
  Handle that FirstRevision is not set for the initial commit
  All situations changed are not causing problems, but it is easier to handle FirstRevision consistently this way.

Should be merged with these three merges, separate PR for 3.4 when approved

Test methodology

Review if FirstRevision usage and Manual
The (meaningless) IRevisionDiffController do not cover arguments in RevisionDiffControl

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✒️ I contribute this code under The Developer Certificate of Origin.

[codecov]

Codecov Report

Merging #8086 into master will increase coverage by 0.02%.
The diff coverage is 58.82%.

@@            Coverage Diff             @@
##           master    #8086      +/-   ##
==========================================
+ Coverage   49.54%   49.57%   +0.02%     
==========================================
  Files         847      848       +1     
  Lines       60916    60957      +41     
  Branches    10924    10927       +3     
==========================================
+ Hits        30182    30217      +35     
- Misses      28497    28504       +7     
+ Partials     2237     2236       -1     

Flag	Coverage Δ
#production	37.37% <31.42%> (+0.01%)	⬆️
#tests	94.86% <87.87%> (+<0.01%)	⬆️

[fsfod]

I guess what happens for "Open with Diff tool" menu entries if the selected file's FirstRevision is null are going to be weird or broken. The only one enabled is "first -> selected" but p4 merge doesn't like "nul" as the second file name idk if thats bug or not. Trying "cherry picked changes" for the same file does nothing idk if it should or not.

[gerhardol]

I guess what happens for "Open with Diff tool" menu entries if the selected file's FirstRevision is null are going to be weird or broken.

This PR handles firstRev==null as "--root", so in supported difftools is works OK
Diff should be handled as for new files

The only one enabled is selected -> first but p4 merge doesn't like "nul" as the second file name idk if thats bug or not. Trying "cherry picked changes" for the same file does nothing idk if it should or not.

A specific problem in p4merge, similar to tortoisemerge but you get a popup
semanticmerge and kdiff3 displays the "diff". Blocking diff for new files would remove this functionality for these tools, just to not show the popup for p4merge

[RussKie]

@fsfod please confirm the fix https://ci.appveyor.com/api/buildjobs/opo96182ksn1sqr2/artifacts/artifacts%2Fpublish%2FGitExtensions-Portable-3.4.0.9417-9d7acd0f9.zip

[fsfod]

Yes the original issue is fixed for me.

[RussKie]

Tests for RevisionDiffInfoProvider changes?

[RussKie]

We're executing this selector multiple times.
Have you considered creating a property on FileStatusList (similar to SelectedGitItems) to simply the call sites?

E.g. something like:

    public sealed partial class FileStatusList : GitModuleControl
    {
        [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
        [Browsable(false)]
        public IEnumerable<FileStatusItem> SelectedGitObjects
        {
            get => SelectedItems
                .Where(i => i.FirstRevision != null)
                .Select(i => i.FirstRevision.ObjectId)
                .Distinct();
        }

[gerhardol]

It was a little like this before, with many access functions. These properties applies to Enumerate for the selected items. Similar could apply to all items etc,
But I do not know how to do this in the best way, I assumed that a static helper on FileStatusItem would not be accepted, so I let that be.
Similar for First, Second, GitStatus.
(I was not ready thinking about this very late with #7899 and did not want to do any more changes...)

SelectedGitItems should be removed too, but it appeared in a little too many places.

[gerhardol]

I added extension methods, OK now?

[gerhardol]

Tests for RevisionDiffInfoProvider changes?

Added tests as well as reordered arguments

[mstv]

👍

[RussKie]

Taking into 3.4