tutorial examples for writing new Clang plugin actions

http://wiki.documentfoundation.org/Clang_plugins

Change-Id: Ieb4fc186490e81ab961c094ca0a7fcdabc0f348f

compilerplugins/README

@@ -40,4 +40,5 @@ Modifications will be written directly to the source files.
 
 == Code documentation / howtos ==
 
-TBD
+http://wiki.documentfoundation.org/Clang_plugins
+

compilerplugins/clang/store/tutorial/tutorial1.cxx

+/*
+ * 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

compilerplugins/clang/store/tutorial/tutorial1.hxx

+/*
+ * 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.
+ *
+ */
+
+#ifndef TUTORIAL1_H
+#define TUTORIAL1_H
+
+#include "plugin.hxx"
+
+namespace loplugin
+{
+
+// The class implementing the plugin action.
+class Tutorial1
+    // Inherits from the Clang class that will allow examing the Clang AST tree (i.e. syntax tree).
+    : public RecursiveASTVisitor< Tutorial1 >
+    // And the base class for LO Clang plugins.
+    , public Plugin
+    {
+    public:
+        // Ctor, nothing special.
+        Tutorial1( ASTContext& context );
+        // The function that will be called to perform the actual action.
+        virtual void run();
+        // Function from Clang, it will be called for every return statement in the source.
+        bool VisitReturnStmt( ReturnStmt* returnstmt );
+    };
+
+} // namespace
+
+#endif // POSTFIXINCREMENTFIX_H
+

compilerplugins/clang/store/tutorial/tutorial1_example.cxx

+// This is just an example file to see what AST looks like for return statements.
+// To the the AST, run :
+// clang++ -fsyntax-only -Xclang -ast-dump tutorial1_example.cxx
+
+void f()
+    {
+    return;
+    }
+
+bool g()
+    {
+    return false;
+    }
+
+bool h()
+    {
+    return 3 > 2;
+    }

compilerplugins/clang/store/tutorial/tutorial2.cxx

+/*
+ * 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

compilerplugins/clang/store/tutorial/tutorial2.hxx

+/*
+ * 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.
+ *
+ */
+
+#ifndef TUTORIAL2_H
+#define TUTORIAL2_H
+
+#include "plugin.hxx"
+
+namespace loplugin
+{
+
+// The same like for Tutorial1.
+class Tutorial2
+    : public RecursiveASTVisitor< Tutorial2 >
+    , public Plugin
+    {
+    public:
+        Tutorial2( ASTContext& context );
+        virtual void run();
+        // Will be called for every if statement.
+        bool VisitIfStmt( IfStmt* ifstmt );
+    private:
+        // Helper function to check if the statement is 'return false;'.
+        bool isReturnFalse( const Stmt* stmt );
+    };
+
+} // namespace
+
+#endif // POSTFIXINCREMENTFIX_H
+

compilerplugins/clang/store/tutorial/tutorial2_example.cxx

+// This is just an example file to see what AST looks like for return statements.
+// To the the AST, run :
+// clang++ -fsyntax-only -Xclang -ast-dump tutorial1_example.cxx
+
+bool g()
+    {
+    if( 1 == 2 )
+        return false;
+    if( 1 == 2 )
+        {
+        return false;
+        }
+    if( true )
+        return false;
+    }

compilerplugins/clang/store/tutorial/tutorial3.cxx

+/*
+ * 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 "tutorial3.hxx"
+
+/*
+This is a rewriter.
+
+It looks for if statements with a comparison followed by literal return false
+and modifies the return statements to 'return maybereturntrue;'
+*/
+
+namespace loplugin
+{
+
+// Ctor, pass arguments.
+Tutorial3::Tutorial3( ASTContext& context, Rewriter& rewriter )
+    : RewritePlugin( context, rewriter )
+    {
+    }
+
+void Tutorial3::run()
+    {
+    TraverseDecl( context.getTranslationUnitDecl());
+    }
+
+bool Tutorial3::VisitIfStmt( IfStmt* ifstmt )
+    {
+    if( ignoreLocation( ifstmt ))
+        return true;
+    if( const BinaryOperator* oper = dyn_cast< BinaryOperator >( ifstmt->getCond()))
+        {
+        if( oper->getOpcode() == BO_EQ )
+            {
+            // Modify the sub-statement if it is 'return false'.
+            modifyReturnFalse( ifstmt->getThen());
+            // Modify the sub-statement if it is '{ return false; }'.
+            if( CompoundStmt* compound = dyn_cast< CompoundStmt >( ifstmt->getThen()))
+                {
+                if( compound->size() == 1 ) // one statement
+                    modifyReturnFalse( *compound->body_begin());
+                }
+            }
+        }
+    return true;
+    }
+
+void Tutorial3::modifyReturnFalse( 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 )
+                { // It is, modify the false to true using LO plugin helper function.
+                replaceText( boolliteral->getSourceRange(), "maybereturntrue" );
+                }
+            }
+        }
+    }
+
+// Register the plugin action with the LO plugin handling.
+static Plugin::Registration< Tutorial3 > X( "tutorial3" );
+
+} // namespace

compilerplugins/clang/store/tutorial/tutorial3.hxx

+/*
+ * 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.
+ *
+ */
+
+#ifndef TUTORIAL3_H
+#define TUTORIAL3_H
+
+#include "plugin.hxx"
+
+namespace loplugin
+{
+
+// Similar like for Tutorial2, but this time the base class is RewritePlugin.
+class Tutorial3
+    : public RecursiveASTVisitor< Tutorial3 >
+    , public RewritePlugin
+    {
+    public:
+        // One more argument for ctor.
+        Tutorial3( ASTContext& context, Rewriter& rewriter );
+        virtual void run();
+        // Will be called for every if statement.
+        bool VisitIfStmt( IfStmt* ifstmt );
+    private:
+        // Helper function to check if the statement is 'return false;' and
+        // modify it if yes.
+        void modifyReturnFalse( const Stmt* stmt );
+    };
+
+} // namespace
+
+#endif // POSTFIXINCREMENTFIX_H
+