fix/issue 2679 (#2680)

* make sure errors are attached with the importing module if the imported module does not exist anymore to prevent later NPEs and loss of information on the current state of the import graph

* changed reloader root location from reloader:/// to prompt:/// to remove a superfluous scheme and to highlight to the user that the origin of the reloading mechanism is the REPL. If a module was imported by the REPL and the reload fails because the file has dissappeared, then this will be the error location

Author: jurgenvinju

src/org/rascalmpl/repl/rascal/RascalInterpreterREPL.java

@@ -231,7 +231,7 @@ public ICommandOutput handleInput(String command) throws InterruptedException, P
                 changes.addAll(dirtyModules);
                 if (!changes.isEmpty()) {
                     dirtyModules.removeAll(changes);
-                    eval.reloadModules(eval.getMonitor(), changes, URIUtil.rootLocation("reloader"));
+                    eval.reloadModules(eval.getMonitor(), changes, URIUtil.rootLocation("prompt"));
                 }
                 return printer.outputResult(eval.eval(eval.getMonitor(), command, PROMPT_LOCATION));
             }

src/org/rascalmpl/semantics/dynamic/Import.java

@@ -480,7 +480,7 @@ public static ITree parseModuleAndFragments(char[] data, ISourceLocation locatio
           ISet extend = Modules.getExtends(top);
           eval.getMonitor().jobTodo(jobName, extend.size());
           for (IValue mod : extend) {
-              evalImport(eval, (IConstructor) mod);
+              evalImport(eval, env, (IConstructor) mod);
               eval.getMonitor().jobStep(jobName, "extending for " + name, 1);
               if (eval.isInterrupted()) {
                 throw new InterruptException(eval.getStackTrace(), eval.getCurrentAST().getLocation());
@@ -503,7 +503,7 @@ public static ITree parseModuleAndFragments(char[] data, ISourceLocation locatio
           ISet imports = Modules.getImports(top);
           eval.getMonitor().jobTodo(jobName, imports.size());
           for (IValue mod : imports) {
-              evalImport(eval, (IConstructor) mod);
+              evalImport(eval, env, (IConstructor) mod);
               eval.getMonitor().jobStep(jobName, "importing for " + name, 1);
               if (eval.isInterrupted()) {
                 throw new InterruptException(eval.getStackTrace(), eval.getCurrentAST().getLocation());
@@ -515,7 +515,7 @@ public static ITree parseModuleAndFragments(char[] data, ISourceLocation locatio
           ISet externals = Modules.getExternals(top);
           eval.getMonitor().jobTodo(jobName, externals.size());
           for (IValue mod : externals) {
-              evalImport(eval, (IConstructor) mod);
+              evalImport(eval, env, (IConstructor) mod);
               eval.getMonitor().jobStep(jobName, "external importing for " + name, 1);
               if (eval.isInterrupted()) {
                 throw new InterruptException(eval.getStackTrace(), eval.getCurrentAST().getLocation());
@@ -575,28 +575,35 @@ private static void declareTypesWhichDoNotNeedImportedModulesAlready(IEvaluator<
       eval.__getTypeDeclarator().evaluateDeclarations(decls, eval.getCurrentEnvt(), true);
   }
 
-  public static void evalImport(IEvaluator<Result<IValue>> eval, IConstructor mod) {
+  /**
+   * Evaluate an import/extend statement in the current module environment, effectively implementing the semantics of import and extend,
+   * and handle any errors that may occur.
+   * 
+   * NB. all errors that flow up to here are reported with the importing module because they make the import/extend unavailable here.
+   * Errors inside of those modules that do not impact this module directly, should have been reported earlier with the module in question, during {@link #loadModule()}.
+   * It is possible that the ModuleEnvironment for the imported/extended module does not even exist here anymore. 
+   */
+  public static void evalImport(IEvaluator<Result<IValue>> eval, ModuleEnvironment importer, IConstructor mod) {
 	  org.rascalmpl.ast.Import imp = (org.rascalmpl.ast.Import) getBuilder().buildValue(mod);
-    String name = Names.fullName(imp.getModule().getName());
 
 	  try {
 		    imp.interpret(eval);
 	  }
-	  catch (Throw rascalException) {
+    catch (Throw rascalException) {
       // when a global initializer throws a runtime exception
-      handleLoadError(eval.getHeap().getModule(name), rascalException.getMessage(), rascalException.getLocation(), rascalException.getTrace().toString());
+      handleLoadError(importer, rascalException.getMessage(), rascalException.getLocation(), rascalException.getTrace().toString());
 	  }
     catch (CyclicExtend | CyclicImportExtend e) {
       // when we end up in a cycle which we can't implement
-      handleLoadError(eval.getHeap().getModule(name), e.getMessage(), e.getLocation(), "");
+      handleLoadError(importer, e.getMessage(), e.getLocation(), "");
     }
     catch (StaticError e) {
       // all other static errors
-      handleLoadError(eval.getHeap().getModule(name), e.getMessage(), e.getLocation(), "");
+      handleLoadError(importer, e.getMessage(), e.getLocation(), "");
     }
 	  catch (Throwable e) {
       // all internal implementation errors that mess up a module's loading
-		  handleLoadError(eval.getHeap().getModule(name), e.getMessage(), imp.getLocation(),
+		  handleLoadError(importer, e.getMessage(), imp.getLocation(),
         Arrays.stream(e.getStackTrace())
             .map(Object::toString)
             .collect(Collectors.joining("\n")));