Do not try merging a single SARIF file

lib/upload-lib.js

@@ -88,6 +88,9 @@ function areAllRunsProducedByCodeQL(sarifFiles) {
 // CodeQL. Otherwise, it will fall back to combining the files in the action.
 // Returns the contents of the combined sarif file.
 async function combineSarifFilesUsingCLI(sarifFiles, gitHubVersion, features, logger) {
+    if (sarifFiles.length === 1) {
+        return JSON.parse(fs.readFileSync(sarifFiles[0], "utf8"));
+    }
     if (!areAllRunsProducedByCodeQL(sarifFiles)) {
         logger.warning("Not all SARIF files were produced by CodeQL. Merging files in the action.");
         // If not, use the naive method of combining the files.

src/upload-lib.ts

@@ -93,6 +93,10 @@ async function combineSarifFilesUsingCLI(
   features: Features,
   logger: Logger,
 ): Promise<SarifFile> {
+  if (sarifFiles.length === 1) {
+    return JSON.parse(fs.readFileSync(sarifFiles[0], "utf8")) as SarifFile;
+  }
+
   if (!areAllRunsProducedByCodeQL(sarifFiles)) {
     logger.warning(
       "Not all SARIF files were produced by CodeQL. Merging files in the action.",