Test compilation errors appear in output diff

[Marcono1234]

Version
CodeQL CLI v2.5.0
Extension version: v1.4.5

Describe the bug
When compilation of a test fails, the extension currently creates an output diff between the expected output and the compilation error, which is pretty pointless and confusing. E.g.:

--- expected
+++ actual
@@ -1,12 +1,1 @@
-| Expressions.java:5:9:5:18 | toString(...) |
-| Expressions.java:9:9:9:13 | ...=... |
-| Expressions.java:10:9:10:11 | ...++ |
-| Expressions.java:11:9:11:20 | new Object(...) |
-| Expressions.java:14:9:14:28 | clone(...) |
+ERROR: no viable parse for input 'a', expecting one of : 'boolean', 'class', 'newtype', 'date', 'float', 'from', 'import', 'int', 'module', 'predicate', 'select', 'string', 'where', Lowerid, Upperid, Atlowerid (Expressions.ql:6,1-2)

It looks like the underlying issue might be caused by the CodeQL CLI which reports this as diff. It appears this is currently 'misused' to perform tests on CodeQL itself, see #608 (comment).
Regardless of whether that is intended or not, the extension could inspect the failureStage of the response, only if it is "failureStage" : "RESULT" the diff should be shown.

To Reproduce

1. Create an .expected file
2. Create a query test file containing a compilation error
3. Run codeql test run --format=json

Expected behavior
Only the compilation error is reported, the diff is not shown.

[aeisenberg]

Thanks for reporting. We've added this to our backlog.

[rysolv-bot]

themanmaran has contributed $25.00 to this issue on Rysolv.

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[aeisenberg]

Thanks for adding a bounty to this @tylermaran. We are happy to accept and facilitate external contributions.

[aeisenberg]

The solution we are considering here would be a better presentation of these kinds of compiler error messages. This would lead to a change in how we parse the output of codeql test in the extension. It would not require any changes to the cli itself.

[eysk-io]

Hi @aeisenberg, I would like to work on this issue if nobody has picked it up yet.

[aeisenberg]

Hi @eyskim, I assigned this issue to you. No one else is currently working on it. Thanks for volunteering!

See here for information on how to run codeql tests in vscode: https://codeql.github.com/docs/codeql-for-visual-studio-code/testing-codeql-queries-in-visual-studio-code/

And the change will likely have to be in this function: https://github.com/github/vscode-codeql/blob/main/extensions/ql-vscode/src/test-adapter.ts#L277-L305