gopls/internal/test: Completion benchmarks use empty range

CL 728881 enforced that gopls completions that pass a `Range` in the
TextDocumentPositionParams only do so with an empty range (start = end).
The benchmark tests weren't enforcing that, so many have been failing.

I fixed the failing tests and added a better error message to the test
code that encourages the regex string to only contain an empty group:
`()`.

Updates golang/go#80113

Change-Id: I1bdb82b4618e6c3eb04506eed93d81166a6a6964
Reviewed-on: https://go-review.googlesource.com/c/tools/+/797720
Reviewed-by: Madeline Kalil <mkalil@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

gopls/internal/test/integration/bench/completion_test.go

diff --git a/gopls/internal/test/integration/bench/completion_test.go b/gopls/internal/test/integration/bench/completion_test.go
index 640c21e..1dbd299 100644
--- a/gopls/internal/test/integration/bench/completion_test.go
+++ b/gopls/internal/test/integration/bench/completion_test.go
@@ -39,6 +39,9 @@
 
 	// Run a completion to make sure the system is warm.
 	loc := env.RegexpSearch(options.file, options.locationRegexp)
+	if !loc.Range.Empty() {
+		b.Errorf("Completion locationRegexp only allows for empty ranges, so use an empty regex group: ()")
+	}
 	completions := env.Completion(loc)
 
 	if testing.Verbose() {
@@ -88,7 +91,7 @@
 
 	benchmarkCompletion(completionBenchOptions{
 		file:           file,
-		locationRegexp: `var testVariable map\[string\]bool = Session{}(\.)`,
+		locationRegexp: `var testVariable map\[string\]bool = Session{}\.()`,
 		setup:          setup,
 	}, b)
 }
@@ -117,7 +120,7 @@
 
 	benchmarkCompletion(completionBenchOptions{
 		file:           file,
-		locationRegexp: `var testVariable \[\]byte (=)`,
+		locationRegexp: `var testVariable \[\]byte =()`,
 		setup:          setup,
 	}, b)
 }
@@ -142,7 +145,7 @@
 
 	benchmarkCompletion(completionBenchOptions{
 		file:           file,
-		locationRegexp: `func \(c \*completer\) _\(\) {\n\tc\.inference\.kindMatches\((c)`,
+		locationRegexp: `func \(c \*completer\) _\(\) {\n\tc\.inference\.kindMatches\(c()`,
 		setup:          setup,
 	}, b)
 }
@@ -152,7 +155,7 @@
 	name           string
 	file           string // repo-relative file to create
 	content        string // file content
-	locationRegexp string // regexp for completion
+	locationRegexp string // regexp for completion, use empty group: ()
 }
 
 var completionTests = []completionTest{
@@ -167,7 +170,7 @@
 	c.inference.kindMatches(c.)
 }
 `,
-		`func \(c \*completer\) _\(\) {\n\tc\.inference\.kindMatches\((c)`,
+		`func \(c \*completer\) _\(\) {\n\tc\.inference\.kindMatches\(c()`,
 	},
 	{
 		"tools",
@@ -305,6 +308,10 @@
 
 	// Run a completion to make sure the system is warm.
 	loc := env.RegexpSearch(test.file, test.locationRegexp)
+	if !loc.Range.Empty() {
+		b.Errorf("Completion locationRegexp only allows for empty ranges, so use an empty regex group: ()")
+	}
+	loc.Range.End = loc.Range.Start
 	completions := env.Completion(loc)
 
 	if testing.Verbose() {
@@ -323,6 +330,9 @@
 			editPlaceholder()
 		}
 		loc := env.RegexpSearch(test.file, test.locationRegexp)
+		if !loc.Range.Empty() {
+			b.Errorf("Completion locationRegexp only allows for empty ranges, so use an empty regex group: ()")
+		}
 		env.Completion(loc)
 	}
 }