fix(release): handle missing release tags gracefully in release-note-generation

java-cloud-bom/release-note-generation/src/main/java/com/google/cloud/ReleaseNoteGeneration.java

@@ -113,16 +113,44 @@ public static void main(String[] arguments)
   }
 
   @VisibleForTesting final StringBuilder report = new StringBuilder();
+  private boolean monorepoReleaseExists = true;
 
   @VisibleForTesting
   ReleaseNoteGeneration() {}
 
+  private static boolean releaseExists(String repository, String tag) {
+    Process process = null;
+    try {
+      ProcessBuilder builder =
+          new ProcessBuilder(
+              "gh", "release", "--repo", GOOGLEAPIS_ORG + "/" + repository, "view", tag);
+      builder.redirectOutput(ProcessBuilder.Redirect.DISCARD);
+      builder.redirectError(ProcessBuilder.Redirect.DISCARD);
+      process = builder.start();
+      boolean finished = process.waitFor(1, TimeUnit.MINUTES);
+      if (!finished) {
+        return false;
+      }
+      return process.exitValue() == 0;
+    } catch (IOException e) {
+      return false;
+    } catch (InterruptedException e) {
+      Thread.currentThread().interrupt();
+      return false;
+    } finally {
+      if (process != null && process.isAlive()) {
+        process.destroyForcibly();
+      }
+    }
+  }
+
   @VisibleForTesting
   String generateReport(Bom bom, String googleCloudJavaVersion)
       throws MavenRepositoryException,
           ArtifactDescriptorException,
           IOException,
           InterruptedException {
+    monorepoReleaseExists = releaseExists("google-cloud-java", "v" + googleCloudJavaVersion);
     Bom previousBom = previousBom(bom);
 
     DefaultArtifact bomArtifact = new DefaultArtifact(bom.getCoordinates());
@@ -422,10 +450,15 @@ private static String releaseUrlForSplitRepo(String libraryName, String version)
         "https://github.com/googleapis/java-%s/releases/tag/v%s", libraryName, version);
   }
 
-  private static String releaseUrlForMonorepo(String libraryName, String version) {
-    // libraryName is unused for the monorepo release note as of Dec 2022
-    return String.format(
-        "https://github.com/googleapis/google-cloud-java/releases/tag/v%s", version);
+  private String releaseUrlForMonorepo(String libraryName, String version) {
+    if (monorepoReleaseExists) {
+      return String.format(
+          "https://github.com/googleapis/google-cloud-java/releases/tag/v%s", version);
+    } else {
+      return String.format(
+          "https://github.com/googleapis/google-cloud-java/releases/tag/v%s-%s",
+          version, libraryName);
+    }
   }
 
   /**
@@ -612,16 +645,43 @@ static String fetchReleaseNote(String owner, String repository, String tag)
       throws IOException, InterruptedException {
     // gh release --repo googleapis/java-storage view v2.16.0
 
-    ProcessBuilder builder =
-        new ProcessBuilder("gh", "release", "--repo", owner + "/" + repository, "view", tag);
-    builder.redirectErrorStream(true);
-    Process process = builder.start();
-    String output =
-        new String(
-            process.getInputStream().readAllBytes(), java.nio.charset.StandardCharsets.UTF_8);
-    boolean finished = process.waitFor(1, TimeUnit.MINUTES);
-    Verify.verify(finished, "The process timed out");
-    Verify.verify(0 == process.exitValue(), "The command failed: %s", output);
-    return output;
+    File tempFile = java.nio.file.Files.createTempFile("gh-release-notes", ".txt").toFile();
+    tempFile.deleteOnExit();
+
+    Process process = null;
+    try {
+      ProcessBuilder builder =
+          new ProcessBuilder("gh", "release", "--repo", owner + "/" + repository, "view", tag);
+      builder.redirectErrorStream(true);
+      builder.redirectOutput(ProcessBuilder.Redirect.to(tempFile));
+
+      process = builder.start();
+      boolean finished = process.waitFor(1, TimeUnit.MINUTES);
+      if (!finished) {
+        throw new IOException("The process timed out");
+      }
+
+      String output =
+          new String(
+              java.nio.file.Files.readAllBytes(tempFile.toPath()),
+              java.nio.charset.StandardCharsets.UTF_8);
+
+      if (process.exitValue() != 0) {
+        String trimmedOutput = output.trim();
+        String lowerOutput = trimmedOutput.toLowerCase();
+        if (lowerOutput.contains("not found") || lowerOutput.contains("404")) {
+          System.err.println(
+              "Warning: The command failed (release likely not found): " + trimmedOutput);
+          return "";
+        }
+        throw new IOException("The command failed: " + trimmedOutput);
+      }
+      return output;
+    } finally {
+      if (process != null && process.isAlive()) {
+        process.destroyForcibly();
+      }
+      tempFile.delete();
+    }
   }
 }