Handling Functions Runtime Environment env var when set by user

release_notes.md

@@ -12,3 +12,4 @@
 - Add `func pack` support for in-proc functions (#4529)
 - Default to remote build for `func pack` for python apps (#4530)
 - Update `func init` to default to the .NET 8 template for in-proc apps (#4557)
+- Fix exception when `AZURE_FUNCTIONS_ENVIRONMENT` variable is set by user (#2465)

src/Cli/func/Actions/HostActions/StartHostAction.cs

@@ -273,7 +273,7 @@ private async Task<IWebHost> BuildWebHost(ScriptApplicationHostOptions hostOptio
                 .Build();
         }
 
-        private async Task<IDictionary<string, string>> GetConfigurationSettings(string scriptPath, Uri uri)
+        internal async Task<IDictionary<string, string>> GetConfigurationSettings(string scriptPath, Uri uri)
         {
             var settings = _secretsManager.GetSecrets();
             settings.Add(Constants.WebsiteHostname, uri.Authority);
@@ -300,7 +300,7 @@ private async Task<IDictionary<string, string>> GetConfigurationSettings(string
 
             // when running locally in CLI we want the host to run in debug mode
             // which optimizes host responsiveness
-            settings.Add("AZURE_FUNCTIONS_ENVIRONMENT", "Development");
+            settings.TryAdd("AZURE_FUNCTIONS_ENVIRONMENT", "Development");
 
             // Inject the .NET Worker startup hook if debugging the worker
             if (DotNetIsolatedDebug != null && DotNetIsolatedDebug.Value)

test/Cli/Func.UnitTests/ActionsTests/StartHostActionTests.cs

@@ -261,6 +261,41 @@ public async Task ValidateHostRuntimeAsync_MatchesExpectedResults(WorkerRuntime
             Assert.False(expectException, "Expected validation failure.");
         }
 
+        [Fact]
+        public async Task GetConfigurationSettings_DoesNotOverwriteAzFuncEnvironment_WhenAlreadyInSecrets()
+        {
+            // Arrange
+            var secretsDict = new Dictionary<string, string>
+            {
+                ["AZURE_FUNCTIONS_ENVIRONMENT"] = "UserEnv"
+            };
+
+            var mockSecretsManager = new Mock<ISecretsManager>();
+            mockSecretsManager.Setup(s => s.GetSecrets())
+                            .Returns(() => new Dictionary<string, string>(secretsDict));
+
+            // Return an empty set of connection strings of the expected type
+            mockSecretsManager.Setup(s => s.GetConnectionStrings())
+                            .Returns(Array.Empty<ConnectionString>);
+
+            // Initialize globals if required by your setup
+            GlobalCoreToolsSettings.Init(mockSecretsManager.Object, []);
+
+            var action = new StartHostAction(mockSecretsManager.Object, Mock.Of<IProcessManager>())
+            {
+                DotNetIsolatedDebug = false,
+                EnableJsonOutput = false,
+                VerboseLogging = false,
+                HostRuntime = "default"
+            };
+
+            // Act
+            var result = await action.GetConfigurationSettings("some/path", new Uri("https://example.com"));
+
+            // Assert
+            Assert.Equal("UserEnv", result["AZURE_FUNCTIONS_ENVIRONMENT"]);
+        }
+
         public void Dispose()
         {
             FileSystemHelpers.Instance = null;