Add debug logging for feature flag enablement

lib/feature-flags.js

@@ -76,6 +76,7 @@ exports.FEATURE_FLAGS_FILE_NAME = "cached-feature-flags.json";
  */
 class Features {
     constructor(gitHubVersion, repositoryNwo, tempDir, logger) {
+        this.logger = logger;
         this.gitHubFeatureFlags = new GitHubFeatureFlags(gitHubVersion, repositoryNwo, path.join(tempDir, exports.FEATURE_FLAGS_FILE_NAME), logger);
     }
     async getDefaultCliVersion(variant) {
@@ -100,22 +101,36 @@ class Features {
         const envVar = (process.env[exports.featureConfig[feature].envVar] || "").toLocaleLowerCase();
         // Do not use this feature if user explicitly disables it via an environment variable.
         if (envVar === "false") {
+            this.logger.debug(`Feature ${feature} is disabled via the environment variable ${exports.featureConfig[feature].envVar}.`);
             return false;
         }
         // Never use this feature if the CLI version explicitly can't support it.
         const minimumVersion = exports.featureConfig[feature].minimumVersion;
         if (codeql && minimumVersion) {
             if (!(await util.codeQlVersionAbove(codeql, minimumVersion))) {
+                this.logger.debug(`Feature ${feature} is disabled because the CodeQL CLI version is older than the minimum ` +
+                    `version ${minimumVersion}.`);
                 return false;
             }
+            else {
+                this.logger.debug(`CodeQL CLI version ${await codeql.getVersion()} is newer than the minimum ` +
+                    `version ${minimumVersion} for feature ${feature}.`);
+            }
         }
         // Use this feature if user explicitly enables it via an environment variable.
         if (envVar === "true") {
+            this.logger.debug(`Feature ${feature} is enabled via the environment variable ${exports.featureConfig[feature].envVar}.`);
             return true;
         }
         // Ask the GitHub API if the feature is enabled.
-        return ((await this.gitHubFeatureFlags.getValue(feature)) ??
-            exports.featureConfig[feature].defaultValue);
+        const apiValue = await this.gitHubFeatureFlags.getValue(feature);
+        if (apiValue !== undefined) {
+            this.logger.debug(`Feature ${feature} is ${apiValue ? "enabled" : "disabled"} via the GitHub API.`);
+            return apiValue;
+        }
+        const defaultValue = exports.featureConfig[feature].defaultValue;
+        this.logger.debug(`Feature ${feature} is ${defaultValue ? "enabled" : "disabled"} due to its default value.`);
+        return defaultValue;
     }
 }
 exports.Features = Features;