Fix activeParameter of signature help when there is no closing paren

[ben-krieger]

In 0.13.0, I believe that activeParameter of signature help is following an incorrect pattern of 0, 0, 1, 2... when the closing right paren is missing. This PR adds tests which cover that case and others and provides a fix.

[ben-krieger]

Tests are failing as expected:

$ ~/.zig/zig-linux-x86_64-0.14.0-dev.3388+e0a955afb/zig build test -Dtest-filter="no right paren"
test
└─ run test 0/1 passed, 1 failed
error: 'lsp_features.signature_help.test.no right paren' failed: expected 1, found 0
/home/ben/.zig/zig-linux-x86_64-0.14.0-dev.3388+e0a955afb/lib/std/testing.zig:103:17: 0x11a21ad in expectEqualInner__anon_32742 (test)
                return error.TestExpectedEqual;
                ^
/home/ben/.zig/zig-linux-x86_64-0.14.0-dev.3388+e0a955afb/lib/std/testing.zig:169:21: 0x11a2288 in expectEqualInner__anon_32736 (test)
                    try expectEqual(expected_payload, actual_payload);
                    ^
/home/ben/src/zls/tests/lsp_features/signature_help.zig:382:5: 0x11a38e6 in testSignatureHelp (test)
    try std.testing.expectEqual(expected_active_parameter, response.activeParameter);
    ^
/home/ben/src/zls/tests/lsp_features/signature_help.zig:68:5: 0x11a432c in test.no right paren (test)
    try testSignatureHelp(
    ^
error: while executing test 'lsp_features.signature_help.test.no right paren', the following test command failed:
/home/ben/src/zls/.zig-cache/o/bbd37958551a3731541edbf7f8d1f980/test --seed=0xf61ad0c1 --cache-dir=/home/ben/src/zls/.zig-cache --listen=-
Build Summary: 12/14 steps succeeded; 1 failed; 0/1 tests passed; 1 failed
test transitive failure
└─ run test 0/1 passed, 1 failed

So the first failed test is this:

fn foo(a: u32, b: u32) void {
    foo(0,<cursor>
}

where the expected activeParameter is 1, but instead 0 is being returned.

[ben-krieger]

The problem seems to be that within getSignatureInfo the lastToken will be .comma whether you're left, on, or right of it. Since for left and on we wish to discard it, we do. But for right, we should not. Unfortunately, without a closing right paren (or any other token), there's no way to tell that we've "passed" the comma.

[ben-krieger]

Pushed a fix for the broken tests. I'd love to see this in 0.14.0, so please let me know how I can help.

[Techatrix]

Thanks for the detailed test coverage. The fix looks good to me.