Fix EnvFile to preserve user-modified values when saving keys only

When SaveKeysOnly is called, it now checks if keys already exist on disk with non-empty values and preserves those values instead of overwriting them. This ensures that user modifications to .env files are not lost during subsequent publish operations.

Co-authored-by: captainsafia <[email protected]>

src/Aspire.Hosting.Docker/EnvFile.cs

@@ -100,6 +100,17 @@ public void Save(string path, bool includeValues)
 
     private void SaveKeysOnly(string path)
     {
+        // Load existing values from disk to preserve user modifications
+        var existingEntries = new Dictionary<string, string?>();
+        if (File.Exists(path))
+        {
+            var existingFile = Load(path);
+            foreach (var entry in existingFile._entries.Values)
+            {
+                existingEntries[entry.Key] = entry.Value;
+            }
+        }
+
         var lines = new List<string>();
 
         foreach (var entry in _entries.Values)
@@ -108,7 +119,19 @@ private void SaveKeysOnly(string path)
             {
                 lines.Add($"# {entry.Comment}");
             }
-            lines.Add($"{entry.Key}=");
+
+            // If the key exists on disk with a non-empty value, preserve it
+            // This ensures user-modified values are not overwritten when we save keys only
+            if (existingEntries.TryGetValue(entry.Key, out var existingValue) && 
+                !string.IsNullOrEmpty(existingValue))
+            {
+                lines.Add($"{entry.Key}={existingValue}");
+            }
+            else
+            {
+                lines.Add($"{entry.Key}=");
+            }
+
             lines.Add(string.Empty);
         }
 

tests/Aspire.Hosting.Docker.Tests/Snapshots/DockerComposePublisherTests.DockerComposeAppendsNewKeysToEnvFileOnPublish#01.verified.env

@@ -1,5 +1,5 @@
 # Parameter param1
-PARAM1=
+PARAM1=changed
 
 # Parameter param2
 PARAM2=

tests/Aspire.Hosting.Docker.Tests/Snapshots/DockerComposePublisherTests.DockerComposeDoesNotOverwriteEnvFileOnPublish#01.verified.env

@@ -1,3 +1,3 @@
 # Parameter param1
-PARAM1=
+PARAM1=changed