StartupContextProvider should expand path environment variable (#5687)

Author: mathewc

src/WebJobs.Script.WebHost/StartupContextProvider.cs

@@ -104,6 +104,7 @@ private StartupContext GetStartupContextOrNull()
             {
                 try
                 {
+                    contextPath = Environment.ExpandEnvironmentVariables(contextPath);
                     _logger.LogDebug($"Loading startup context from {contextPath}");
                     string content = File.ReadAllText(contextPath);
 

test/WebJobs.Script.Tests/StartupContextProviderTests.cs

@@ -141,6 +141,15 @@ public void GetContext_InvalidPath_ReturnsNull()
             VerifyLastLog(LogLevel.Error, "Failed to load startup context");
         }
 
+        [Fact]
+        public void GetContext_ExpandsEnvironmentVariables()
+        {
+            string path = Path.Combine("%TEMP%", $"{Guid.NewGuid()}.txt");
+            WriteStartupContext(path: path);
+
+            Assert.NotNull(_startupContextProvider.Context);
+        }
+
         [Fact]
         public void GetContext_EnvVarNotSet_ReturnsNull()
         {
@@ -193,9 +202,10 @@ public void SetContext_AppliesHostAssignmentContext()
             Assert.Equal(_secrets.Host.System, secrets.SystemKeys);
         }
 
-        private string WriteStartupContext(string context = null)
+        private string WriteStartupContext(string context = null, string path = null)
         {
-            var path = Path.Combine(Path.GetTempPath(), $"{Guid.NewGuid()}.txt");
+            path = path ?? Path.Combine(Path.GetTempPath(), $"{Guid.NewGuid()}.txt");
+            path = Environment.ExpandEnvironmentVariables(path);
             _environment.SetEnvironmentVariable(EnvironmentSettingNames.AzureWebsiteStartupContextCache, path);
 
             if (context == null)