ILC: Use temporary file to prevent invalid object files on compilation errors

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/Logger.cs

@@ -41,6 +41,8 @@ public class Logger
 
         public bool IsVerbose { get; }
 
+        public bool HasLoggedErrors { get; private set; }
+
         public Logger(
             ILogWriter writer,
             ILProvider ilProvider,
@@ -93,14 +95,22 @@ public void LogWarning(string text, int code, MessageOrigin origin, string subca
         {
             MessageContainer? warning = MessageContainer.CreateWarningMessage(this, text, code, origin, subcategory);
             if (warning.HasValue)
+            {
+                if (warning.Value.Category == MessageCategory.WarningAsError)
+                    HasLoggedErrors = true;
                 _logWriter.WriteWarning(warning.Value);
+            }
         }
 
         public void LogWarning(MessageOrigin origin, DiagnosticId id, params string[] args)
         {
             MessageContainer? warning = MessageContainer.CreateWarningMessage(this, origin, id, args);
             if (warning.HasValue)
+            {
+                if (warning.Value.Category == MessageCategory.WarningAsError)
+                    HasLoggedErrors = true;
                 _logWriter.WriteWarning(warning.Value);
+            }
         }
 
         public void LogWarning(string text, int code, TypeSystemEntity origin, string subcategory = MessageSubCategory.None) =>
@@ -137,14 +147,20 @@ public void LogError(string text, int code, string subcategory = MessageSubCateg
         {
             MessageContainer? error = MessageContainer.CreateErrorMessage(text, code, subcategory, origin);
             if (error.HasValue)
+            {
+                HasLoggedErrors = true;
                 _logWriter.WriteError(error.Value);
+            }
         }
 
         public void LogError(MessageOrigin? origin, DiagnosticId id, params string[] args)
         {
             MessageContainer? error = MessageContainer.CreateErrorMessage(origin, id, args);
             if (error.HasValue)
+            {
+                HasLoggedErrors = true;
                 _logWriter.WriteError(error.Value);
+            }
         }
 
         public void LogError(string text, int code, TypeSystemEntity origin, string subcategory = MessageSubCategory.None) =>

src/coreclr/tools/aot/ILCompiler/Program.cs

@@ -638,7 +638,9 @@ void RunScanner()
             if (sourceLinkFileName != null)
                 dumpers.Add(new SourceLinkWriter(sourceLinkFileName));
 
-            CompilationResults compilationResults = compilation.Compile(outputFilePath, ObjectDumper.Compose(dumpers));
+            // Write to a temporary file and rename on success to avoid leaving partial files on failure
+            string tempOutputFilePath = outputFilePath + ".tmp";
+            CompilationResults compilationResults = compilation.Compile(tempOutputFilePath, ObjectDumper.Compose(dumpers));
             string exportsFile = Get(_command.ExportsFile);
             if (exportsFile != null)
             {
@@ -713,6 +715,26 @@ static bool IsRelatedToInvalidInput(MethodDesc method)
 
             preinitManager.LogStatistics(logger);
 
+            // If errors were produced (including warnings treated as errors), delete the temporary file
+            // and return error code to avoid misleading build systems into thinking the compilation succeeded.
+            if (logger.HasLoggedErrors)
+            {
+                try
+                {
+                    File.Delete(tempOutputFilePath);
+                }
+                catch
+                {
+                    // If we can't delete the temp file, there's not much we can do.
+                    // The compilation will still fail due to logged errors.
+                }
+
+                return 1;
+            }
+
+            // Rename the temporary file to the final output file
+            File.Move(tempOutputFilePath, outputFilePath, overwrite: true);
+
             return 0;
         }