RD-11521: report connection failures to the user

[bgaidioz]

Before the pool was global, the code logic was that a connection failure to FDW would be an internal bug, FDW should always be available, and the connection pool should be provisioned to match the expected usage.

To review carefully if this behavior is what we want, and is implemented properly: To report connection failures to the user, we should isolate the connection failure SQLException (those are identified with code 08xxx), and process these ones as errors that are normal to hit sometimes:

• for execute, validate and getProgramDescription, they are caught are the message is reported (as a String or ErrorMessage with positions when needed). The validate and getProgramDescription need positions, I've put positions spanning the full code.
• for hover, we probably should ignore it and and do not report type info,
• for connection errors occuring in metadata caches, we do not report the error to the user (I think), and since we can't connect, store an empty list of matches. That entry will be wiped after the usual timeout.

The PR only adds tests to execute,validate and getProgramDescription and LSP calls.

[miguelbranco80]

One comment is that we found a slightly different behaviour when doing LSP calls vs validate/execute calls. So we should indeed be sure for the behaviour we want for LSP. Probably it is indeed safe to ignore as you mention for the hover.

[bgaidioz]

One comment is that we found a slightly different behaviour when doing LSP calls vs validate/execute calls. So we should indeed be sure for the behaviour we want for LSP. Probably it is indeed safe to ignore as you mention for the hover.

I added tests that trigger both errors for LSP calls, ensuring they return nothing silently. There was even a place missing the try.

// hover returns nothing
val hoverResponse = runHover(compilerService, joe, "SELECT * FROM example.airports", Pos(1, 17))
assert(hoverResponse.completion.isEmpty)
val hoverResponse2 =
  runHover(compilerService, joe, "SELECT * FROM example.airports WHERE :id = airport_id", Pos(1, 40))
assert(hoverResponse2.completion.isEmpty)
// we get no word completions
val wordCompletionResponse = runWordCompletion(compilerService, joe, "SELECT * FROM exa", "exa", Pos(1, 17))
assert(wordCompletionResponse.completions.isEmpty)
// we get no dot completions
val dotCompletionResponse = runDotCompletion(compilerService, joe, "SELECT * FROM example.", Pos(1, 22))
assert(dotCompletionResponse.completions.isEmpty)