Use cache for incremental builds

Author: mdh1418

src/mono/sample/HelloWorld/HelloWorld.csproj

@@ -26,6 +26,7 @@
       OutputDir="$(PublishDir)"
       IntermediateOutputPath="$(IntermediateOutputPath)"
       UseAotDataFile="$(UseAotDataFile)"
+      CacheFilePath="$(IntermediateOutputPath)aot_compiler_cache.json"
       NetTracePath="$(NetTracePath)"
       PgoBinaryPath="$(PgoBinaryPath)"
       MibcProfilePath="$(MibcProfilePath)">

src/tasks/AotCompilerTask/MonoAOTCompiler.cs

@@ -425,6 +425,20 @@ private bool ProcessNettrace(string netTraceFile)
     {
         var outputMibcPath = Path.Combine(OutputDir, Path.ChangeExtension(Path.GetFileName(netTraceFile), ".mibc"));
 
+        if (_cache!.Enabled)
+        {
+            string hash = Utils.ComputeHash(netTraceFile);
+            if (!_cache!.UpdateAndCheckHasFileChanged($"-mibc-source-file-{Path.GetFileName(netTraceFile)}", hash))
+            {
+                Log.LogMessage(MessageImportance.Low, $"Skipping generating {outputMibcPath} from {netTraceFile} because source file hasn't changed");
+                return true;
+            }
+            else
+            {
+                Log.LogMessage(MessageImportance.Low, $"Generating {outputMibcPath} from {netTraceFile} because the source file's hash has changed.");
+            }
+        }
+
         (int exitCode, string output) = Utils.TryRunProcess(Log,
                                                             PgoBinaryPath!,
                                                             $"create-mibc --trace {netTraceFile} --output {outputMibcPath}");
@@ -876,12 +890,13 @@ private PrecompileArguments GetPrecompileArgumentsFor(ITaskItem assemblyItem, st
     private bool PrecompileLibrary(PrecompileArguments args)
     {
         string assembly = args.AOTAssembly.GetMetadata("FullPath");
+        string output;
         try
         {
             string msgPrefix = $"[{Path.GetFileName(assembly)}] ";
 
             // run the AOT compiler
-            (int exitCode, string output) = Utils.TryRunProcess(Log,
+            (int exitCode, output) = Utils.TryRunProcess(Log,
                                                                 CompilerBinaryPath,
                                                                 $"--response=\"{args.ResponseFilePath}\"",
                                                                 args.EnvironmentVariables,
@@ -921,6 +936,12 @@ private bool PrecompileLibrary(PrecompileArguments args)
         bool copied = false;
         foreach (var proxyFile in args.ProxyFiles)
         {
+            if (!File.Exists(proxyFile.TempFile))
+            {
+                Log.LogError($"Precompile command succeeded, but can't find the expected temporary output file - {proxyFile.TempFile} for {assembly}.{Environment.NewLine}{output}");
+                return false;
+            }
+
             copied |= proxyFile.CopyOutputFileIfChanged();
             _fileWrites.Add(proxyFile.TargetFile);
         }
@@ -1135,8 +1156,20 @@ public FileCache(string? cacheFilePath, TaskLoggingHelper log)
         _newCache = new(_oldCache.FileHashes);
     }
 
+    public bool UpdateAndCheckHasFileChanged(string filePath, string newHash)
+    {
+        if (!Enabled)
+            throw new InvalidOperationException("Cache is not enabled. Make sure the cache file path is set");
+
+        _newCache!.FileHashes[filePath] = newHash;
+        return !_oldCache!.FileHashes.TryGetValue(filePath, out string? oldHash) || oldHash != newHash;
+    }
+
     public bool ShouldCopy(ProxyFile proxyFile, [NotNullWhen(true)] out string? cause)
     {
+        if (!Enabled)
+            throw new InvalidOperationException("Cache is not enabled. Make sure the cache file path is set");
+
         cause = null;
 
         string newHash = Utils.ComputeHash(proxyFile.TempFile);
@@ -1194,6 +1227,9 @@ public bool CopyOutputFileIfChanged()
 
         try
         {
+            if (!File.Exists(TempFile))
+                throw new LogAsErrorException($"Could not find the temporary file {TempFile} for target file {TargetFile}. Look for any errors/warnings generated earlier in the build.");
+
             if (!_cache.ShouldCopy(this, out string? cause))
             {
                 _cache.Log.LogMessage(MessageImportance.Low, $"Skipping copying over {TargetFile} as the contents are unchanged");