add check for empty github workflow uses

The value isn't actually empty in the testcase which triggered the
panic, but our GitHub workflow library doesn't currently support parsing
GitHub's new  YAML anchors/aliases.

https://github.blog/changelog/2025-09-18-actions-yaml-anchors-and-non-public-workflow-templates/

Signed-off-by: Spencer Schrock <[email protected]>

Author: spencerschrock

checks/raw/pinned_dependencies.go

@@ -789,7 +789,7 @@ var validateGitHubActionWorkflow fileparser.DoWhileTrueOnFileContent = func(
 					fmt.Sprintf("unable to parse step '%v' for job '%v'", jobName, stepName))
 			}
 
-			if execAction == nil || execAction.Uses == nil {
+			if execAction == nil || execAction.Uses == nil || execAction.Uses.Value == "" {
 				// Cannot check further, continue.
 				continue
 			}

checks/raw/pinned_dependencies_test.go

@@ -77,6 +77,11 @@ func TestGithubWorkflowPinning(t *testing.T) {
 			filename: "./testdata/.github/workflows/github-workflow-unknown-os.yaml",
 			warns:    2, // 1 in job with unknown OS, 1 in job with known OS
 		},
+		{
+			name:     "YAML anchor usage doesn't panic",
+			filename: "./testdata/.github/workflows/workflow-anchor.yaml",
+			warns:    1, // anchor definition is unpinned, but alias isn't supported by actionlint
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

checks/raw/testdata/.github/workflows/workflow-anchor.yaml

@@ -0,0 +1,30 @@
+# Copyright 2025 OpenSSF Scorecard Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+name: CI
+
+on:
+  push:
+
+jobs:
+  yaml-anchor:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Upload coverage artifact
+        uses: &actions-upload-artifact actions/[email protected]
+
+  yaml-alias:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Upload coverage artifact
+        uses: *actions-upload-artifact