Allow absent inputs to use import contexts

internal/engine/glob_test.go

@@ -268,6 +268,48 @@ func TestFilesystemContextIsValidatedWithoutImportsOrActiveOverlay(t *testing.T)
 	}
 }
 
+func TestNoSourceImportsAndFilesystemContext(t *testing.T) {
+	t.Parallel()
+
+	directory := t.TempDir()
+	for _, imports := range []bool{false, true} {
+		name := "imports disabled"
+		if imports {
+			name = "imports enabled"
+		}
+		t.Run(name, func(t *testing.T) {
+			result, err := testLoad[importTestConfig](NoSource(), Options[importTestConfig]{
+				Imports: imports, Filesystem: &FilesystemContext{Root: directory},
+			})
+			if err != nil {
+				t.Fatal(err)
+			}
+			if sources := result.Sources(); len(sources) != 0 {
+				t.Fatalf("NoSource sources = %#v", sources)
+			}
+			if _, ok := result.Metadata().Lookup(Keys("items", "root")); ok {
+				t.Fatal("NoSource contributed explicit input")
+			}
+		})
+	}
+
+	outside := t.TempDir()
+	for _, test := range []struct {
+		name    string
+		context FilesystemContext
+		code    Code
+	}{
+		{name: "missing root", context: FilesystemContext{BaseDir: directory}, code: CodeOptionsInvalid},
+		{name: "relative root", context: FilesystemContext{Root: "."}, code: CodeOptionsInvalid},
+		{name: "missing root directory", context: FilesystemContext{Root: filepath.Join(directory, "missing")}, code: CodeImportInvalid},
+		{name: "base outside root", context: FilesystemContext{BaseDir: outside, Root: directory}, code: CodeImportOutsideRoot},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			requireLoadCode(t, NoSource(), Options[importTestConfig]{Filesystem: &test.context}, test.code)
+		})
+	}
+}
+
 func writeGlobRoot(t *testing.T, directory, pattern string, required bool) string {
 	t.Helper()
 	requiredLine := ""