gopls/internal/regtest: fix regtest failures from "undefined" errors

Following-up on CL 434636, also update gopls regtests to handle the new
"undefined: ..." errors replacing "undeclared name: ..." errors in
go/types.

Change-Id: I53a05623b63851e8165ab3685aff2cdf494fa5b6
Reviewed-on: https://go-review.googlesource.com/c/tools/+/434639
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>

gopls/internal/lsp/code_action.go

@@ -261,6 +261,12 @@ func importDiagnostics(fix *imports.ImportFix, diagnostics []protocol.Diagnostic
 			if ident == fix.IdentName {
 				results = append(results, diagnostic)
 			}
+		// "undefined: X" may be an unresolved import at Go 1.20+.
+		case strings.HasPrefix(diagnostic.Message, "undefined: "):
+			ident := strings.TrimPrefix(diagnostic.Message, "undefined: ")
+			if ident == fix.IdentName {
+				results = append(results, diagnostic)
+			}
 		// "could not import: X" may be an invalid import.
 		case strings.HasPrefix(diagnostic.Message, "could not import: "):
 			ident := strings.TrimPrefix(diagnostic.Message, "could not import: ")

gopls/internal/regtest/diagnostics/diagnostics_test.go

@@ -618,7 +618,7 @@ func main() {
 			env.RegexpReplace("x/x.go", `package x`, `package main`)
 			env.Await(OnceMet(
 				env.DoneWithChange(),
-				env.DiagnosticAtRegexpWithMessage("x/main.go", `fmt`, "undeclared name")))
+				env.DiagnosticAtRegexp("x/main.go", `fmt`)))
 		}
 	})
 }
@@ -1800,7 +1800,7 @@ var Bar = Foo
 
 	Run(t, files, func(t *testing.T, env *Env) {
 		env.OpenFile("foo.go")
-		env.Await(env.DiagnosticAtRegexpWithMessage("bar.go", `Foo`, "undeclared name"))
+		env.Await(env.DiagnosticAtRegexp("bar.go", `Foo`))
 		env.RegexpReplace("foo.go", `\+build`, "")
 		env.Await(EmptyDiagnostics("bar.go"))
 	})
@@ -1831,15 +1831,15 @@ package main
 		env.OpenFile("main.go")
 		env.OpenFile("other.go")
 		env.Await(
-			env.DiagnosticAtRegexpWithMessage("main.go", "asdf", "undeclared name"),
-			env.DiagnosticAtRegexpWithMessage("main.go", "fdas", "undeclared name"),
+			env.DiagnosticAtRegexp("main.go", "asdf"),
+			env.DiagnosticAtRegexp("main.go", "fdas"),
 		)
 		env.SetBufferContent("other.go", "package main\n\nasdf")
 		// The new diagnostic in other.go should not suppress diagnostics in main.go.
 		env.Await(
 			OnceMet(
 				env.DiagnosticAtRegexpWithMessage("other.go", "asdf", "expected declaration"),
-				env.DiagnosticAtRegexpWithMessage("main.go", "asdf", "undeclared name"),
+				env.DiagnosticAtRegexp("main.go", "asdf"),
 			),
 		)
 	})
@@ -2082,7 +2082,7 @@ func F[T C](_ T) {
 		var d protocol.PublishDiagnosticsParams
 		env.Await(
 			OnceMet(
-				env.DiagnosticAtRegexpWithMessage("main.go", `C`, "undeclared name"),
+				env.DiagnosticAtRegexp("main.go", `C`),
 				ReadDiagnostics("main.go", &d),
 			),
 		)

gopls/internal/regtest/workspace/workspace_test.go

@@ -1157,8 +1157,8 @@ func (Server) Foo() {}
 		// as invalid. So we need to wait for the metadata of main_test.go to be
 		// updated before moving other_test.go back to the main_test package.
 		env.Await(
-			env.DiagnosticAtRegexpWithMessage("other_test.go", "Server", "undeclared"),
-			env.DiagnosticAtRegexpWithMessage("main_test.go", "otherConst", "undeclared"),
+			env.DiagnosticAtRegexp("other_test.go", "Server"),
+			env.DiagnosticAtRegexp("main_test.go", "otherConst"),
 		)
 		env.RegexpReplace("other_test.go", "main", "main_test")
 		env.Await(