Keep the break which follows an opening parenthesis

[virzak]

Closes #152.

The issue's remaining item was the line break before the first argument, which the analysis there said was already gone from the syntax tree by the time UnwrapExtension ran, cause unlocated. It is VisitArgumentList:

if (invalid.Contains(node.Arguments.Count - 1))
{
    retval = retval
        .WithCloseParenToken(@base.CloseParenToken.WithLeadingTrivia())
        .WithOpenParenToken(@base.OpenParenToken.WithTrailingTrivia());
}

Roslyn puts the newline that follows a token in that token's trailing trivia, so stripping the opening parenthesis's trailing trivia is stripping the break after (. That is right when the list empties - ( and ) should meet - but the condition is only that the last argument went, which is every call ending in a CancellationToken. So the break went, and the first argument kept the indentation which had placed it at the start of a line:

ProgressMethod(            1,
    2);

Now it is stripped only when nothing remains to put on that line. ArgumentTests.KeepLineBreaksWhenTheLastArgumentIsDropped covers this with no extension methods involved, which is where the bug actually lives.

That in turn unblocks the half of UnwrapExtension which #152 recorded as not working. With the list still broken where it was written to break, the receiver can take the line the argument it displaces was starting, and the comma between them can take the break:

-WriteTo(stream, destination,
+WriteTo(
+        stream,
+        destination,
         4096,
         progress: progress);

One test changes meaning

CSharp_14_ExtensionUnwrapsOntoOneLine asserted that a two argument call collapsed onto a single line. That was never designed - #150 added the test to cover the receiver's own trivia, and the collapsing came from this bug removing a break the author had written. The generator preserves the layout it is given everywhere else, so preserving it here too is the consistent answer, and the test is renamed to CSharp_14_ExtensionDropsTheChainBreakAfterTheReceiver to say what it was built to cover.

If you would rather short lists collapse, that is a formatting decision the generator does not currently make anywhere, and worth its own issue rather than resting on this bug.

337 tests pass on net10.0, 295 on net472, clean build.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.80%. Comparing base (002c0ed) to head (f0ffc4f).

Files with missing lines	Patch %	Lines
...rc/Zomp.SyncMethodGenerator/AsyncToSyncRewriter.cs	83.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #163      +/-   ##
==========================================
- Coverage   93.90%   93.80%   -0.10%     
==========================================
  Files           9        9              
  Lines        1576     1583       +7     
  Branches      363      365       +2     
==========================================
+ Hits         1480     1485       +5     
- Misses         25       26       +1     
- Partials       71       72       +1     

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