tutorial examples for writing new Clang plugin actions

http://wiki.documentfoundation.org/Clang_plugins

Change-Id: Ieb4fc186490e81ab961c094ca0a7fcdabc0f348f

compilerplugins/clang/store/tutorial/tutorial2.cxx

@@ -0,0 +1,92 @@
+/*
+ * 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 "tutorial2.hxx"
+
+/*
+This is a compile check.
+
+Warns about if statements with a comparison followed by literal return false:
+if( a == 1 )
+    return false;
+*/
+
+namespace loplugin
+{
+
+Tutorial2::Tutorial2( ASTContext& context )
+    : Plugin( context )
+    {
+    }
+
+void Tutorial2::run()
+    {
+    // The Clang AST helper class will call VisitIfStmt for every if statement.
+    TraverseDecl( context.getTranslationUnitDecl());
+    }
+
+// This function is called for every if statement.
+bool Tutorial2::VisitIfStmt( IfStmt* ifstmt )
+    {
+    if( ignoreLocation( ifstmt ))
+        return true;
+    // Check if the condition of the if statement is a binary operator.
+    if( const BinaryOperator* oper = dyn_cast< BinaryOperator >( ifstmt->getCond()))
+        {
+        // And if it's operator==.
+        if( oper->getOpcode() == BO_EQ )
+            {
+            // Now check if the sub-statement is 'return false'.
+            const Stmt* warn = NULL; // The return statement (for the warning message).
+            // Check if the sub-statement is directly 'return false;'.
+            if( isReturnFalse( ifstmt->getThen()))
+                warn = ifstmt->getThen();
+            // Check if the sub-statement is '{ return false; }'
+            else if( CompoundStmt* compound = dyn_cast< CompoundStmt >( ifstmt->getThen()))
+                {
+                if( compound->size() == 1 ) // one statement
+                    if( isReturnFalse( *compound->body_begin())) // check the one sub-statement
+                        warn = *compound->body_begin();
+                }
+            if( warn != NULL ) // there is a return statement to warn about.
+                {
+                report( DiagnosticsEngine::Warning,
+                    "returning false after if with equality comparison",
+                    cast< ReturnStmt >( warn )->getRetValue()->getLocStart()) // the 'false' in the return
+                    << warn->getSourceRange();
+                // Also add a note showing the if statement.
+                report( DiagnosticsEngine::Note,
+                    "the if statement is here",
+                    ifstmt->getLocStart());
+                }
+            }
+        }
+    return true;
+    }
+
+bool Tutorial2::isReturnFalse( const Stmt* stmt )
+    {
+    // Is it return statement?
+    if( const ReturnStmt* returnstmt = dyn_cast< ReturnStmt >( stmt ))
+        {
+        // dyn_cast_or_null<> can also be passed NULL, unlike dyn_cast<>
+        if( const CXXBoolLiteralExpr* boolliteral = dyn_cast_or_null< CXXBoolLiteralExpr >( returnstmt->getRetValue()))
+            {
+            if( boolliteral->getValue() == false )
+                return true;
+            }
+        }
+    return false;
+    }
+
+// Register the plugin action with the LO plugin handling.
+static Plugin::Registration< Tutorial2 > X( "tutorial2" );
+
+} // namespace