Bug 1324239 - Refactor the clang plugin; r=mystor

This patch mostly just splits up clang-plugin.cpp into separate files for
different classes or helpers.

build/clang-plugin/AssertAssignmentChecker.cpp

@@ -0,0 +1,24 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "AssertAssignmentChecker.h"
+#include "CustomMatchers.h"
+
+void AssertAssignmentChecker::registerMatcher(MatchFinder& AstMatcher) {
+  AstMatcher.addMatcher(
+      callExpr(isAssertAssignmentTestFunc()).bind("funcCall"),
+      this);
+}
+
+void AssertAssignmentChecker::run(
+    const MatchFinder::MatchResult &Result) {
+  DiagnosticsEngine &Diag = Result.Context->getDiagnostics();
+  unsigned AssignInsteadOfComp = Diag.getDiagnosticIDs()->getCustomDiagID(
+      DiagnosticIDs::Error, "Forbidden assignment in assert expression");
+  const CallExpr *FuncCall = Result.Nodes.getNodeAs<CallExpr>("funcCall");
+
+  if (FuncCall && hasSideEffectAssignment(FuncCall)) {
+    Diag.Report(FuncCall->getLocStart(), AssignInsteadOfComp);
+  }
+}