Allow manually provided function.json file. Closes #50

src/Microsoft.NET.Sdk.Functions/MakeFunction/BuildArtifactsLog.cs

@@ -0,0 +1,74 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+namespace MakeFunctionJson
+{
+    internal class BuildArtifactsLog
+    {
+        private const string buildArtifactsLogName = "functionsSdk.out";
+        private readonly HashSet<string> _artifacts;
+        private readonly FakeLogger _logger;
+        private readonly string _logPath;
+
+        public BuildArtifactsLog(string outputPath, FakeLogger logger)
+        {
+            _logger = logger;
+            _artifacts = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+            _logPath = Path.Combine(outputPath, buildArtifactsLogName);
+            try
+            {
+                if (File.Exists(_logPath))
+                {
+                    foreach (var line in File.ReadAllLines(_logPath))
+                    {
+                        _artifacts.Add(line);
+                    }
+                }
+            }
+            catch (Exception e)
+            {
+                _logger.LogWarning($"Unable to read file {_logPath}");
+                _logger.LogWarningFromException(e);
+            }
+        }
+
+        public bool TryClearBuildArtifactsLog()
+        {
+            return Try(() => File.Delete(_logPath), $"Unable to clean file '{_logPath}'", true);
+        }
+
+        public bool TryAddBuildArtifact(string name)
+        {
+            return Try(() => File.AppendAllLines(_logPath, new[] { name }), $"Unable to update file '{_logPath}'", true);
+        }
+
+        public bool IsBuildArtifact(string name)
+        {
+            return _artifacts.Contains(name);
+        }
+
+        private bool Try(Action action, string message, bool isError)
+        {
+            try
+            {
+                action();
+                return true;
+            }
+            catch (Exception e)
+            {
+                if (isError)
+                {
+                    _logger.LogError(message);
+                    _logger.LogErrorFromException(e);
+                }
+                else
+                {
+                    _logger.LogWarning(message);
+                    _logger.LogWarningFromException(e);
+                }
+                return false;
+            }
+        }
+    }
+}

src/Microsoft.NET.Sdk.Functions/MakeFunction/FunctionJsonConverter.cs

@@ -14,6 +14,7 @@ internal class FunctionJsonConverter
         private string _outputPath;
         private readonly FakeLogger _log;
         private readonly IDictionary<string, MethodInfo> _functionNamesSet;
+        private readonly BuildArtifactsLog _buildArtifactsLog;
 
         internal FunctionJsonConverter(string assemblyPath, string outputPath, TaskLoggingHelper log)
         {
@@ -35,6 +36,7 @@ internal FunctionJsonConverter(string assemblyPath, string outputPath, TaskLoggi
             }
             _log = new FakeLogger(log);
             _functionNamesSet = new Dictionary<string, MethodInfo>(StringComparer.OrdinalIgnoreCase);
+            _buildArtifactsLog = new BuildArtifactsLog(_outputPath, _log);
         }
 
         /// <summary>
@@ -54,6 +56,12 @@ internal bool TryRun()
             try
             {
                 this._functionNamesSet.Clear();
+                if (!_buildArtifactsLog.TryClearBuildArtifactsLog())
+                {
+                    _log.LogError("Unable to clean build artifacts file.");
+                    return false;
+                }
+
                 CleanOutputPath();
 #if NET46
                 var assembly = Assembly.LoadFrom(_assemblyPath);
@@ -69,8 +77,11 @@ internal bool TryRun()
                         {
                             var functionJson = method.ToFunctionJson(relativeAssemblyPath);
                             var functionName = method.GetSdkFunctionName();
-                            var path = Path.Combine(_outputPath, functionName, "function.json");
-                            if (CheckAppSettingsAndFunctionName(functionJson, method))
+                            var artifactName = Path.Combine(functionName, "function.json");
+                            var path = Path.Combine(_outputPath, artifactName);
+                            if (!File.Exists(path) &&
+                                CheckAppSettingsAndFunctionName(functionJson, method) &&
+                                _buildArtifactsLog.TryAddBuildArtifact(artifactName))
                             {
                                 functionJson.Serialize(path);
                             }
@@ -171,6 +182,7 @@ private void CleanOutputPath()
             Directory.GetDirectories(_outputPath)
                 .Select(d => Path.Combine(d, "function.json"))
                 .Where(File.Exists)
+                .Where(f => _buildArtifactsLog.IsBuildArtifact(f.Replace(_outputPath, string.Empty)))
                 .Select(Path.GetDirectoryName)
                 .ToList()
                 .ForEach(directory =>