tutorial examples for writing new Clang plugin actions

http://wiki.documentfoundation.org/Clang_plugins

Change-Id: Ieb4fc186490e81ab961c094ca0a7fcdabc0f348f

compilerplugins/clang/store/tutorial/tutorial1.cxx

@@ -0,0 +1,65 @@
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * Based on LLVM/Clang.
+ *
+ * This file is distributed under the University of Illinois Open Source
+ * License. See LICENSE.TXT for details.
+ *
+ */
+
+#include "tutorial1.hxx"
+
+/*
+This is a compile check.
+
+Checks all return statements and warns if they return literal false (i.e. 'return false').
+*/
+
+namespace loplugin
+{
+
+// Ctor, nothing special, pass the argument(s).
+Tutorial1::Tutorial1( ASTContext& context )
+    : Plugin( context )
+    {
+    }
+
+// Perform the actual action.
+void Tutorial1::run()
+    {
+    // Traverse the whole AST of the translation unit (i.e. examine the whole source file).
+    // The Clang AST helper class will call VisitReturnStmt for every return statement.
+    TraverseDecl( context.getTranslationUnitDecl());
+    }
+
+// This function is called for every return statement.
+// Returning true means to continue with examining the AST, false means to stop (just always return true).
+bool Tutorial1::VisitReturnStmt( ReturnStmt* returnstmt )
+    {
+    // Helper function from the LO base plugin class, call at the very beginning to ignore sources
+    // that should not be processed (e.g. system headers).
+    if( ignoreLocation( returnstmt ))
+        return true;
+    // Get the expression in the return statement (see ReturnStmt API docs).
+    const Expr* expression = returnstmt->getRetValue();
+    if( expression == NULL )
+        return true; // plain 'return;' without expression
+    // Check if the expression is a bool literal (Clang uses dyn_cast<> instead of dynamic_cast<>).
+    if( const CXXBoolLiteralExpr* boolliteral = dyn_cast< CXXBoolLiteralExpr >( expression ))
+        { // It is.
+        if( boolliteral->getValue() == false ) // Is it 'return false;' ? (See CXXBoolLiteralExpr API docs)
+            { // Ok, warn, use LO plugin helper function.
+            report( DiagnosticsEngine::Warning, // It's just a warning.
+                "returning false",  // the message
+                boolliteral->getLocStart()) // and the exact position where the message should point
+                    << returnstmt->getSourceRange(); // and the full return statement to highlight (optional)
+            }
+        }
+    return true;
+    }
+
+// Register the plugin action with the LO plugin handling.
+static Plugin::Registration< Tutorial1 > X( "tutorial1" );
+
+} // namespace