gopls/internal/regtest: fix TestFailingDiagnosticClearingOnEdit

This test was asserting immediately on the non-presence of published
diagnostics, and therefore was racing with the diagnostics calculation
pass. Following https://go.dev/cl/420539 this became a flake, because
once gopls has calculated diagnostics for the open event, it will
actually publish empty diagnostics for the opened file.

Update the test to use a OnceMet so that we only evaluate the
expectation once we've finished the diagnostics pass. As a result, the
test deterministically failed, which was fixed by using the
EmptyOrNoDiagnostics expectation.

Fixes golang/go#54271

Change-Id: Id3f220ce44c7996132699a724b6c627f034e367f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/422136
gopls-CI: kokoro <[email protected]>
Run-TryBot: Robert Findley <[email protected]>
Reviewed-by: Peter Weinberger <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

gopls/internal/regtest/misc/failures_test.go

@@ -39,9 +39,12 @@ func main() {
 	})
 }
 
-// badPackageDup contains a duplicate definition of the 'a' const.
-// this is from diagnostics_test.go,
-const badPackageDup = `
+// This test demonstrates a case where gopls is confused by line directives,
+// and fails to surface type checking errors.
+func TestFailingDiagnosticClearingOnEdit(t *testing.T) {
+	// badPackageDup contains a duplicate definition of the 'a' const.
+	// this is from diagnostics_test.go,
+	const badPackageDup = `
 -- go.mod --
 module mod.com
 
@@ -56,11 +59,17 @@ package consts
 const a = 2
 `
 
-func TestFailingDiagnosticClearingOnEdit(t *testing.T) {
 	Run(t, badPackageDup, func(t *testing.T, env *Env) {
 		env.OpenFile("b.go")
+
 		// no diagnostics for any files, but there should be
-		env.Await(NoDiagnostics("a.go"), NoDiagnostics("b.go"))
+		env.Await(
+			OnceMet(
+				env.DoneWithOpen(),
+				EmptyOrNoDiagnostics("a.go"),
+				EmptyOrNoDiagnostics("b.go"),
+			),
+		)
 
 		// Fix the error by editing the const name in b.go to `b`.
 		env.RegexpReplace("b.go", "(a) = 2", "b")

internal/lsp/regtest/env.go

@@ -282,6 +282,7 @@ func (a *Awaiter) DiagnosticsFor(name string) *protocol.PublishDiagnosticsParams
 }
 
 func (e *Env) Await(expectations ...Expectation) {
+	e.T.Helper()
 	if err := e.Awaiter.Await(e.Ctx, expectations...); err != nil {
 		e.T.Fatal(err)
 	}