8 files changed, 84 insertions, 2 deletions
diff --git a/Changelog.md b/Changelog.md
index 1e16df59..c9d80432 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 bodies that are not blocks.
  * 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..0bc20f2e 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(), "Variable declarations can only be used inside blocks.");
+}
+
+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..f5716bf9 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;
diff --git a/test/libsolidity/syntaxTests/variableDeclaration/do_while.sol b/test/libsolidity/syntaxTests/variableDeclaration/do_while.sol
new file mode 100644
index 00000000..8fc48b33
--- /dev/null
+++ b/test/libsolidity/syntaxTests/variableDeclaration/do_while.sol
@@ -0,0 +1,12 @@
+pragma solidity >0.4.24;
+
+contract C
+{
+	function f(uint x) public pure {
+		do
+			uint y;
+		while (x > 0);
+	}
+}
+// ----
+// SyntaxError: (81-87): Variable declarations can only be used inside blocks.
diff --git a/test/libsolidity/syntaxTests/variableDeclaration/else.sol b/test/libsolidity/syntaxTests/variableDeclaration/else.sol
new file mode 100644
index 00000000..914e0c0c
--- /dev/null
+++ b/test/libsolidity/syntaxTests/variableDeclaration/else.sol
@@ -0,0 +1,13 @@
+pragma solidity >0.4.24;
+
+contract C
+{
+	function f(uint x) public pure {
+		if (x > 0)
+			{uint y;}
+		else
+			uint z;
+	}
+}
+// ----
+// SyntaxError: (109-115): Variable declarations can only be used inside blocks.
diff --git a/test/libsolidity/syntaxTests/variableDeclaration/for.sol b/test/libsolidity/syntaxTests/variableDeclaration/for.sol
new file mode 100644
index 00000000..bc137f93
--- /dev/null
+++ b/test/libsolidity/syntaxTests/variableDeclaration/for.sol
@@ -0,0 +1,11 @@
+pragma solidity >0.4.24;
+
+contract C
+{
+	function f(uint x) public pure {
+		for (uint i = 0; i < x; ++i)
+			uint y;
+	}
+}
+// ----
+// SyntaxError: (107-113): Variable declarations can only be used inside blocks.
diff --git a/test/libsolidity/syntaxTests/variableDeclaration/if.sol b/test/libsolidity/syntaxTests/variableDeclaration/if.sol
new file mode 100644
index 00000000..75ab2026
--- /dev/null
+++ b/test/libsolidity/syntaxTests/variableDeclaration/if.sol
@@ -0,0 +1,11 @@
+pragma solidity >0.4.24;
+
+contract C
+{
+	function f(uint x) public pure {
+		if (x > 0)
+			uint y;
+	}
+}
+// ----
+// SyntaxError: (89-95): Variable declarations can only be used inside blocks.
diff --git a/test/libsolidity/syntaxTests/variableDeclaration/while.sol b/test/libsolidity/syntaxTests/variableDeclaration/while.sol
new file mode 100644
index 00000000..2997d80c
--- /dev/null
+++ b/test/libsolidity/syntaxTests/variableDeclaration/while.sol
@@ -0,0 +1,11 @@
+pragma solidity >0.4.24;
+
+contract C
+{
+	function f(uint x) public pure {
+		while (x > 0)
+			uint y;
+	}
+}
+// ----
+// SyntaxError: (92-98): Variable declarations can only be used inside blocks.