Handle erroring during early mod construction phases, and actually report that into the error UI

by doing armslength exception handling and propagation.

Signed-off-by: cpw <cpw+github@weeksfamily.ca>

src/main/java/net/minecraftforge/fml/ModLoader.java

@@ -268,8 +268,10 @@ public class ModLoader
         final Map<String, IModInfo> modInfoMap = modFile.getModFileInfo().getMods().stream().collect(Collectors.toMap(IModInfo::getModId, Function.identity()));
 
         LOGGER.debug(LOADING, "ModContainer is {}", ModContainer.class.getClassLoader());
-        final List<ModContainer> containers = modFile.getScanResult().getTargets().entrySet().stream().
+        final List<ModContainer> containers = modFile.getScanResult().getTargets()
-                map(e -> buildModContainerFromTOML(modFile, modClassLoader, modInfoMap, e))
+                .entrySet()
+                .stream()
+                .map(e -> buildModContainerFromTOML(modFile, modClassLoader, modInfoMap, e))
                 .filter(Objects::nonNull)
                 .collect(Collectors.toList());
         if (containers.size() != modInfoMap.size()) {
@@ -279,7 +281,8 @@ public class ModLoader
                     modInfoMap.size(), modInfoMap.values().stream().map(IModInfo::getModId).sorted().collect(Collectors.toList()));
             loadingExceptions.add(new ModLoadingException(null, ModLoadingStage.CONSTRUCT, "fml.modloading.missingclasses", null, modFile.getFilePath()));
         }
-        return containers;
+        // remove errored mod containers
+        return containers.stream().filter(obj -> !(obj instanceof ErroredModContainer)).collect(Collectors.toList());
     }
 
     private ModContainer buildModContainerFromTOML(final ModFile modFile, final TransformingClassLoader modClassLoader, final Map<String, IModInfo> modInfoMap, final Map.Entry<String, ? extends IModLanguageProvider.IModLanguageLoader> idToProviderEntry) {
@@ -291,9 +294,10 @@ public class ModLoader
                     orElseThrow(()->new ModLoadingException(null, ModLoadingStage.CONSTRUCT, "fml.modloading.missingmetadata", null, modId));
             return languageLoader.loadMod(info, modClassLoader, modFile.getScanResult());
         } catch (ModLoadingException mle) {
-            // exceptions are caught and added to the error list for later handling. Null is returned here.
+            // exceptions are caught and added to the error list for later handling
             loadingExceptions.add(mle);
-            return null;
+            // return an errored container instance here, because we tried and failed building a container.
+            return new ErroredModContainer(mle);
         }
     }
 
@@ -336,4 +340,20 @@ public class ModLoader
     public static boolean isDataGenRunning () {
         return runningDataGen;
     }
+
+    static class ErroredModContainer extends ModContainer {
+        public ErroredModContainer(final ModLoadingException mle) {
+            super(mle.getModInfo());
+        }
+
+        @Override
+        public boolean matches(final Object mod) {
+            return false;
+        }
+
+        @Override
+        public Object getMod() {
+            return null;
+        }
+    }
 }

src/main/java/net/minecraftforge/fml/javafmlmod/FMLJavaModLanguageProvider.java

@@ -19,6 +19,10 @@
 
 package net.minecraftforge.fml.javafmlmod;
 
+import cpw.mods.modlauncher.api.LamdbaExceptionUtils;
+import net.minecraftforge.fml.ModLoadingException;
+import net.minecraftforge.fml.ModLoadingStage;
+import net.minecraftforge.fml.common.Mod;
 import net.minecraftforge.forgespi.language.ILifecycleEvent;
 import net.minecraftforge.forgespi.language.IModLanguageProvider;
 import net.minecraftforge.forgespi.language.IModInfo;
@@ -39,7 +43,6 @@ import static net.minecraftforge.fml.Logging.*;
 
 public class FMLJavaModLanguageProvider implements IModLanguageProvider
 {
-
     private static final Logger LOGGER = LogManager.getLogger();
 
     private static class FMLModTarget implements IModLanguageProvider.IModLanguageLoader {
@@ -72,10 +75,24 @@ public class FMLJavaModLanguageProvider implements IModLanguageProvider
                 final Constructor<?> constructor = fmlContainer.getConstructor(IModInfo.class, String.class, ClassLoader.class, ModFileScanData.class);
                 return (T)constructor.newInstance(info, className, modClassLoader, modFileScanResults);
             }
-            catch (NoSuchMethodException | ClassNotFoundException | InstantiationException | IllegalAccessException | InvocationTargetException e)
+            // ALL exception handling has to be done through the classloader, because we're loaded in the wrong context, so any classes we just blind load will be in the wrong
+            // class loading context. Funky but works.
+            catch (InvocationTargetException e) {
+                LOGGER.fatal(LOADING, "Failed to build mod", e);
+                final Class<RuntimeException> mle = (Class<RuntimeException>)LamdbaExceptionUtils.uncheck(()->Class.forName("net.minecraftforge.fml.ModLoadingException", true, Thread.currentThread().getContextClassLoader()));
+                if (mle.isInstance(e.getTargetException())) {
+                    throw mle.cast(e.getTargetException());
+                } else {
+                    final Class<ModLoadingStage> mls = (Class<ModLoadingStage>) LamdbaExceptionUtils.uncheck(()->Class.forName("net.minecraftforge.fml.ModLoadingStage", true, Thread.currentThread().getContextClassLoader()));
+                    throw LamdbaExceptionUtils.uncheck(()->LamdbaExceptionUtils.uncheck(()->mle.getConstructor(IModInfo.class, mls, String.class, Throwable.class)).newInstance(info, Enum.valueOf(mls, "CONSTRUCT"), "fml.modloading.failedtoloadmodclass", e));
+                }
+            }
+            catch (NoSuchMethodException | ClassNotFoundException | InstantiationException | IllegalAccessException e)
             {
                 LOGGER.fatal(LOADING,"Unable to load FMLModContainer, wut?", e);
-                throw new RuntimeException(e);
+                final Class<RuntimeException> mle = (Class<RuntimeException>)LamdbaExceptionUtils.uncheck(()->Class.forName("net.minecraftforge.fml.ModLoadingException", true, Thread.currentThread().getContextClassLoader()));
+                final Class<ModLoadingStage> mls = (Class<ModLoadingStage>) LamdbaExceptionUtils.uncheck(()->Class.forName("net.minecraftforge.fml.ModLoadingStage", true, Thread.currentThread().getContextClassLoader()));
+                throw LamdbaExceptionUtils.uncheck(()->LamdbaExceptionUtils.uncheck(()->mle.getConstructor(IModInfo.class, mls, String.class, Throwable.class)).newInstance(info, Enum.valueOf(mls, "CONSTRUCT"), "fml.modloading.failedtoloadmodclass", e));
             }
         }
     }