Disallow single statement var decl in if/while/for without blocks

3 files changed, 26 insertions, 2 deletions

diff --git a/Changelog.md b/Changelog.md
index 1e16df59..ec494c41 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -68,6 +68,7 @@ Breaking Changes:
  * Syntax Checker: Named return values in function types are an error.
  * Syntax Checker: Strictly require visibility specifier for functions. This was already the case in the experimental 0.5.0 mode.
  * Syntax Checker: Disallow unary ``+``. This was already the case in the experimental 0.5.0 mode.
+ * Syntax Checker: Disallow single statement variable declaration inside if/while/for without a block.
  * View Pure Checker: Strictly enfore state mutability. This was already the case in the experimental 0.5.0 mode.
 
 Language Features:
diff --git a/libsolidity/analysis/SyntaxChecker.cpp b/libsolidity/analysis/SyntaxChecker.cpp
index ac4fa72b..1b5c00c4 100644
--- a/libsolidity/analysis/SyntaxChecker.cpp
+++ b/libsolidity/analysis/SyntaxChecker.cpp
@@ -138,9 +138,25 @@ void SyntaxChecker::endVisit(ModifierDefinition const& _modifier)
 	m_placeholderFound = false;
 }
 
-bool SyntaxChecker::visit(WhileStatement const&)
+void SyntaxChecker::checkSingleStatementVariableDeclaration(ASTNode const* _statement)
+{
+	auto varDecl = dynamic_cast<VariableDeclarationStatement const*>(_statement);
+	if (varDecl)
+		m_errorReporter.syntaxError(_statement->location(), "Invalid variable declaration. Please declare it inside a block.");
+}
+
+bool SyntaxChecker::visit(IfStatement const& _ifStatement)
+{
+	checkSingleStatementVariableDeclaration(&_ifStatement.trueStatement());
+	if (Statement const* _statement = _ifStatement.falseStatement())
+		checkSingleStatementVariableDeclaration(_statement);
+	return true;
+}
+
+bool SyntaxChecker::visit(WhileStatement const& _whileStatement)
 {
 	m_inLoopDepth++;
+	checkSingleStatementVariableDeclaration(&_whileStatement.body());
 	return true;
 }
 
@@ -149,9 +165,10 @@ void SyntaxChecker::endVisit(WhileStatement const&)
 	m_inLoopDepth--;
 }
 
-bool SyntaxChecker::visit(ForStatement const&)
+bool SyntaxChecker::visit(ForStatement const& _forStatement)
 {
 	m_inLoopDepth++;
+	checkSingleStatementVariableDeclaration(&_forStatement.body());
 	return true;
 }
 
diff --git a/libsolidity/analysis/SyntaxChecker.h b/libsolidity/analysis/SyntaxChecker.h
index 897df676..27d98401 100644
--- a/libsolidity/analysis/SyntaxChecker.h
+++ b/libsolidity/analysis/SyntaxChecker.h
@@ -52,6 +52,12 @@ private:
 	virtual bool visit(ModifierDefinition const& _modifier) override;
 	virtual void endVisit(ModifierDefinition const& _modifier) override;
 
+	// Reports an error if _statement is a VariableDeclarationStatement.
+	// Used by if/while/for to check for single statement variable declarations
+	// without a block.
+	void checkSingleStatementVariableDeclaration(ASTNode const* _statement);
+
+	virtual bool visit(IfStatement const& _ifStatement) override;
 	virtual bool visit(WhileStatement const& _whileStatement) override;
 	virtual void endVisit(WhileStatement const& _whileStatement) override;
 	virtual bool visit(ForStatement const& _forStatement) override;