Don't apply bundle version limits if host is in placeholder mode (#11316)

Author: soninaren

release_notes.md

@@ -5,4 +5,5 @@
 -->
 - Add JitTrace files for v4.43 (#11277)
 - Cap v4.x extension bundle versions on .NET 6 to the range (>4.2.0, <4.22.0) by default (#11289)
-- Update `Microsoft.Azure.WebJobs` reference to `3.0.42` (#11310)
+- Update `Microsoft.Azure.WebJobs` reference to `3.0.42` (#11310)
+- Don't apply bundle version limits if host is in placeholder mode (#11316)

src/WebJobs.Script/ExtensionBundle/ExtensionBundleManager.cs

@@ -281,9 +281,11 @@ internal string FindBestVersionMatch(VersionRange versionRange, IEnumerable<stri
         }
 
         // Applies bundle version limits for .NET 6, using the default bundle if referencing a v4 major bundle version.
+        // Does not apply version limit in placeholder mode. This will prevent bundle download in placeholder mode as long as a matching bundle is available.
         private VersionRange GetAdjustedVersion(int dotnetVersion, VersionRange versionRange, string bundleId)
         {
-            if (dotnetVersion != 6
+            if (_environment.IsPlaceholderModeEnabled()
+                || dotnetVersion != 6
                 || !string.Equals(bundleId, ScriptConstants.DefaultExtensionBundleId, StringComparison.OrdinalIgnoreCase)
                 || versionRange.MinVersion.Major != ScriptConstants.ExtensionBundleV4MajorVersion)
             {

test/WebJobs.Script.Tests/ExtensionBundle/ExtensionBundleManagerTests.cs

@@ -684,6 +684,48 @@ public void FindBestVersionMatch_V4Range_NoCaps_MixedSet_PicksHighest()
 #endif
 
 #if NET6_0
+
+        [Fact]
+        public void FindBestVersionMatch_V4Range_PlaceholderMode_AllowsPreviouslyCappedMin()
+        {
+            // Without placeholder mode, only version "4.2.0" would be excluded by the adjusted open interval (4.2.0, 4.22.0),
+            // resulting in a null match (covered by existing test FindBestVersionMatch_V4Range_AllFiltered_ReturnsNull).
+            // With placeholder mode enabled, adjustment is skipped and "4.2.0" is valid and should be selected.
+            var range = VersionRange.Parse("[4.0.0, 5.0.0)");
+            var versions = new List<string> { "4.2.0" };
+
+            var options = GetTestExtensionBundleOptions(BundleId, "[4.*,5.0.0)");
+            var env = GetTestAppServiceEnvironment();
+            env.SetEnvironmentVariable(AzureWebsitePlaceholderMode, "1"); // enable placeholder mode
+
+            var manager = GetExtensionBundleManager(options, env);
+
+            var resolved = manager.FindBestVersionMatch(range, versions, ScriptConstants.DefaultExtensionBundleId, new FunctionsHostingConfigOptions());
+
+            Assert.Equal("4.2.0", resolved);
+        }
+
+        [Fact]
+        public void FindBestVersionMatch_V4Range_PlaceholderMode_AllowsPreviouslyCappedOuterVersions()
+        {
+            // Version adjustment on .NET 6 would cap effective range to (4.2.0, 4.22.0) (exclusive on both ends),
+            // excluding 4.2.0, 4.22.0, and anything above (e.g., 4.23.0). Normal (non-placeholder) selection (with provided list)
+            // would therefore choose 4.21.9 (if present) or next highest inside interval.
+            // With placeholder mode enabled, no adjustment occurs and the highest (4.23.0) should be selected.
+            var range = VersionRange.Parse("[4.0.0, 5.0.0)");
+            var versions = new List<string> { "4.2.0", "4.3.0", "4.21.9", "4.22.0", "4.23.0" };
+
+            var options = GetTestExtensionBundleOptions(BundleId, "[4.*,5.0.0)");
+            var env = GetTestAppServiceEnvironment();
+            env.SetEnvironmentVariable(AzureWebsitePlaceholderMode, "1"); // enable placeholder mode
+
+            var manager = GetExtensionBundleManager(options, env);
+
+            var resolved = manager.FindBestVersionMatch(range, versions, ScriptConstants.DefaultExtensionBundleId, new FunctionsHostingConfigOptions());
+
+            Assert.Equal("4.23.0", resolved);
+        }
+
         [Fact]
         public void FindBestVersionMatch_V4Range_MinCapApplied_ExcludesCappedMin()
         {