Add verification target for empty pop

libsolidity/formal/CHC.cpp

@@ -98,17 +98,45 @@ void CHC::analyze(SourceUnit const& _source)
 
 	for (auto const& [scope, target]: m_verificationTargets)
 	{
-		auto assertions = transactionAssertions(scope);
-		for (auto const* assertion: assertions)
+		if (target.type == VerificationTarget::Type::Assert)
 		{
+			auto assertions = transactionAssertions(scope);
+			for (auto const* assertion: assertions)
+			{
+				createErrorBlock();
+				connectBlocks(target.value, error(), target.constraints && (target.errorId == assertion->id()));
+				auto [result, model] = query(error(), assertion->location());
+				// This should be fine but it's a bug in the old compiler
+				(void)model;
+				if (result == smt::CheckResult::UNSATISFIABLE)
+					m_safeAssertions.insert(assertion);
+			}
+		}
+		else if (target.type == VerificationTarget::Type::PopEmptyArray)
+		{
+			solAssert(dynamic_cast<FunctionCall const*>(scope), "");
 			createErrorBlock();
-			connectBlocks(target.value, error(), target.constraints && (target.errorId == assertion->id()));
-			auto [result, model] = query(error(), assertion->location());
+			connectBlocks(target.value, error(), target.constraints && (target.errorId == scope->id()));
+			auto [result, model] = query(error(), scope->location());
 			// This should be fine but it's a bug in the old compiler
 			(void)model;
-			if (result == smt::CheckResult::UNSATISFIABLE)
-				m_safeAssertions.insert(assertion);
+			if (result != smt::CheckResult::UNSATISFIABLE)
+			{
+				string msg = "Empty array \"pop\" ";
+				if (result == smt::CheckResult::SATISFIABLE)
+					msg += "detected here.";
+				else
+					msg += "might happen here.";
+				m_unsafeTargets.insert(scope);
+				m_outerErrorReporter.warning(
+					2529_error,
+					scope->location(),
+					msg
+				);
+			}
 		}
+		else
+			solAssert(false, "");
 	}
 }
 
@@ -161,7 +189,7 @@ void CHC::endVisit(ContractDefinition const& _contract)
 	auto stateExprs = vector<smt::Expression>{m_error.currentValue()} + currentStateVariables();
 	setCurrentBlock(*m_constructorSummaryPredicate, &stateExprs);
 
-	addVerificationTarget(m_currentContract, m_currentBlock, smt::Expression(true), m_error.currentValue());
+	addAssertVerificationTarget(m_currentContract, m_currentBlock, smt::Expression(true), m_error.currentValue());
 	connectBlocks(m_currentBlock, interface(), m_error.currentValue() == 0);
 
 	SMTEncoder::endVisit(_contract);
@@ -256,7 +284,7 @@ void CHC::endVisit(FunctionDefinition const& _function)
 
 			if (_function.isPublic())
 			{
-				addVerificationTarget(&_function, m_currentBlock, sum, assertionError);
+				addAssertVerificationTarget(&_function, m_currentBlock, sum, assertionError);
 				connectBlocks(m_currentBlock, iface, sum && (assertionError == 0));
 			}
 		}
@@ -556,10 +584,34 @@ void CHC::unknownFunctionCall(FunctionCall const&)
 	m_unknownFunctionCallSeen = true;
 }
 
+void CHC::makeArrayPopVerificationTarget(FunctionCall const& _arrayPop)
+{
+	FunctionType const& funType = dynamic_cast<FunctionType const&>(*_arrayPop.expression().annotation().type);
+	solAssert(funType.kind() == FunctionType::Kind::ArrayPop, "");
+
+	auto memberAccess = dynamic_cast<MemberAccess const*>(&_arrayPop.expression());
+	solAssert(memberAccess, "");
+	auto symbArray = dynamic_pointer_cast<smt::SymbolicArrayVariable>(m_context.expression(memberAccess->expression()));
+	solAssert(symbArray, "");
+
+	auto previousError = m_error.currentValue();
+	m_error.increaseIndex();
+
+	addArrayPopVerificationTarget(&_arrayPop, m_error.currentValue());
+	connectBlocks(
+		m_currentBlock,
+		m_currentFunction->isConstructor() ? summary(*m_currentContract) : summary(*m_currentFunction),
+		currentPathConditions() && symbArray->length() <= 0 && m_error.currentValue() == _arrayPop.id()
+	);
+
+	m_context.addAssertion(m_error.currentValue() == previousError);
+}
+
 void CHC::resetSourceAnalysis()
 {
 	m_verificationTargets.clear();
 	m_safeAssertions.clear();
+	m_unsafeTargets.clear();
 	m_functionAssertions.clear();
 	m_callGraph.clear();
 	m_summaries.clear();
@@ -974,9 +1026,35 @@ pair<smt::CheckResult, vector<string>> CHC::query(smt::Expression const& _query,
 	return {result, values};
 }
 
-void CHC::addVerificationTarget(ASTNode const* _scope, smt::Expression _from, smt::Expression _constraints, smt::Expression _errorId)
+void CHC::addVerificationTarget(
+	ASTNode const* _scope,
+	VerificationTarget::Type _type,
+	smt::Expression _from,
+	smt::Expression _constraints,
+	smt::Expression _errorId
+)
 {
-	m_verificationTargets.emplace(_scope, CHCVerificationTarget{{VerificationTarget::Type::Assert, _from, _constraints}, _errorId});
+	m_verificationTargets.emplace(_scope, CHCVerificationTarget{{_type, _from, _constraints}, _errorId});
+}
+
+void CHC::addAssertVerificationTarget(ASTNode const* _scope, smt::Expression _from, smt::Expression _constraints, smt::Expression _errorId)
+{
+	addVerificationTarget(_scope, VerificationTarget::Type::Assert, _from, _constraints, _errorId);
+}
+
+void CHC::addArrayPopVerificationTarget(ASTNode const* _scope, smt::Expression _errorId)
+{
+	solAssert(m_currentContract, "");
+	solAssert(m_currentFunction, "");
+
+	if (m_currentFunction->isConstructor())
+		addVerificationTarget(_scope, VerificationTarget::Type::PopEmptyArray, summary(*m_currentContract), smt::Expression(true), _errorId);
+	else
+	{
+		auto iface = (*m_interfaces.at(m_currentContract))(initialStateVariables());
+		auto sum = summary(*m_currentFunction);
+		addVerificationTarget(_scope, VerificationTarget::Type::PopEmptyArray, iface, sum, _errorId);
+	}
 }
 
 string CHC::uniquePrefix()

libsolidity/formal/CHC.h

@@ -78,6 +78,7 @@ private:
 	void visitAssert(FunctionCall const& _funCall);
 	void internalFunctionCall(FunctionCall const& _funCall);
 	void unknownFunctionCall(FunctionCall const& _funCall);
+	void makeArrayPopVerificationTarget(FunctionCall const& _arrayPop) override;
 	//@}
 
 	struct IdCompare
@@ -182,7 +183,9 @@ private:
 	/// @returns <false, model> otherwise.
 	std::pair<smt::CheckResult, std::vector<std::string>> query(smt::Expression const& _query, langutil::SourceLocation const& _location);
 
-	void addVerificationTarget(ASTNode const* _scope, smt::Expression _from, smt::Expression _constraints, smt::Expression _errorId);
+	void addVerificationTarget(ASTNode const* _scope, VerificationTarget::Type _type, smt::Expression _from, smt::Expression _constraints, smt::Expression _errorId);
+	void addAssertVerificationTarget(ASTNode const* _scope, smt::Expression _from, smt::Expression _constraints, smt::Expression _errorId);
+	void addArrayPopVerificationTarget(ASTNode const* _scope, smt::Expression _errorId);
 	//@}
 
 	/// Misc.
@@ -245,6 +248,8 @@ private:
 
 	/// Assertions proven safe.
 	std::set<Expression const*> m_safeAssertions;
+	/// Targets proven unsafe.
+	std::set<ASTNode const*> m_unsafeTargets;
 	//@}
 
 	/// Control-flow.

libsolidity/formal/SMTEncoder.cpp

@@ -1115,8 +1115,13 @@ void SMTEncoder::arrayPop(FunctionCall const& _funCall)
 	solAssert(memberAccess, "");
 	auto symbArray = dynamic_pointer_cast<smt::SymbolicArrayVariable>(m_context.expression(memberAccess->expression()));
 	solAssert(symbArray, "");
+
+	makeArrayPopVerificationTarget(_funCall);
+
 	auto oldElements = symbArray->elements();
 	auto oldLength = symbArray->length();
+	m_context.addAssertion(oldLength > 0);
+
 	symbArray->increaseIndex();
 	m_context.addAssertion(symbArray->elements() == oldElements);
 	auto newLength = smt::Expression::ite(
@@ -1124,7 +1129,7 @@ void SMTEncoder::arrayPop(FunctionCall const& _funCall)
 		smt::maxValue(*TypeProvider::uint256()),
 		oldLength - 1
 	);
-	m_context.addAssertion(symbArray->length() == newLength);
+	m_context.addAssertion(symbArray->length() == oldLength - 1);
 
 	arrayPushPopAssign(memberAccess->expression(), symbArray->currentValue());
 }

libsolidity/formal/SMTEncoder.h

@@ -140,6 +140,9 @@ protected:
 	void arrayPush(FunctionCall const& _funCall);
 	void arrayPop(FunctionCall const& _funCall);
 	void arrayPushPopAssign(Expression const& _expr, smt::Expression const& _array);
+	/// Allows BMC and CHC to create verification targets for popping
+	/// an empty array.
+	virtual void makeArrayPopVerificationTarget(FunctionCall const&) {}
 
 	/// Division expression in the given type. Requires special treatment because
 	/// of rounding for signed division.
@@ -244,7 +247,7 @@ protected:
 
 	struct VerificationTarget
 	{
-		enum class Type { ConstantCondition, Underflow, Overflow, UnderOverflow, DivByZero, Balance, Assert } type;
+		enum class Type { ConstantCondition, Underflow, Overflow, UnderOverflow, DivByZero, Balance, Assert, PopEmptyArray } type;
 		smt::Expression value;
 		smt::Expression constraints;
 	};

test/libsolidity/smtCheckerTests/array_members/pop_1_safe.sol

@@ -0,0 +1,9 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[] a;
+	function f() public {
+		a.push();
+		a.pop();
+	}
+}

test/libsolidity/smtCheckerTests/array_members/pop_1_unsafe.sol

@@ -0,0 +1,10 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[] a;
+	function f() public {
+		a.pop();
+	}
+}
+// ----
+// Warning: (82-89): Empty array "pop" detected here.

test/libsolidity/smtCheckerTests/array_members/pop_2d_safe.sol

@@ -0,0 +1,10 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[][] a;
+	function f() public {
+		a.push();
+		a[0].push();
+		a[0].pop();
+	}
+}

test/libsolidity/smtCheckerTests/array_members/pop_2d_unsafe.sol

@@ -0,0 +1,10 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[][] a;
+	function f() public {
+		a.push();
+		a[0].push();
+		a[1].pop();
+	}
+}

test/libsolidity/smtCheckerTests/array_members/pop_constructor_safe.sol

@@ -0,0 +1,9 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[] a;
+	constructor() public {
+		a.push();
+		a.pop();
+	}
+}

test/libsolidity/smtCheckerTests/array_members/pop_constructor_unsafe.sol

@@ -0,0 +1,8 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[] a;
+	constructor() public {
+		a.pop();
+	}
+}

test/libsolidity/smtCheckerTests/array_members/pop_loop_safe.sol

@@ -0,0 +1,11 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[] a;
+	function f(uint l) public {
+		for (uint i = 0; i < l; ++i) {
+			a.push();
+			a.pop();
+		}
+	}
+}

test/libsolidity/smtCheckerTests/array_members/pop_loop_unsafe.sol

@@ -0,0 +1,12 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[] a;
+	function f(uint l) public {
+		for (uint i = 0; i < l; ++i) {
+			a.push();
+			a.pop();
+		}
+		a.pop();
+	}
+}

test/libsolidity/smtCheckerTests/array_members/push_2d_arg_1_safe.sol

@@ -3,10 +3,7 @@ pragma experimental SMTChecker;
 contract C {
 	uint[][] a;
 	function f(uint[] memory x, uint y) public {
-		require(a.length < 100000);
 		a.push(x);
-		assert(a[a.length - 1][0] == x[0]);
-		require(a[0].length < 100000);
 		a[0].push(y);
 		assert(a[0][a[0].length - 1] == y);
 	}

test/libsolidity/smtCheckerTests/array_members/push_2d_arg_1_unsafe.sol

@@ -0,0 +1,11 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[][] a;
+	function f(uint[] memory x, uint y) public {
+		a.push(x);
+		a[0].push(y);
+		a[0].pop();
+		assert(a[0][a[0].length - 1] == y);
+	}
+}

test/libsolidity/smtCheckerTests/array_members/push_arg_1.sol

@@ -3,7 +3,6 @@ pragma experimental SMTChecker;
 contract C {
 	uint[] a;
 	function f(uint x) public {
-		require(a.length < 100000);
 		a.push(x);
 		assert(a[a.length - 1] == x);
 	}

test/libsolidity/smtCheckerTests/array_members/push_overflow_1_safe_no_overflow_assumption.sol

@@ -8,4 +8,3 @@ contract C {
 		assert(x[0] == 42);
 	}
 }
-// ----

test/libsolidity/smtCheckerTests/array_members/push_overflow_2_safe_no_overflow_assumption.sol

@@ -11,5 +11,3 @@ contract C {
 		assert(x[0] == 42);
 	}
 }
-
-// ----

test/libsolidity/smtCheckerTests/array_members/push_zero_2d_safe.sol

@@ -0,0 +1,10 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[][] a;
+	function f() public {
+		a.push();
+		a[0].push();
+		assert(a[a.length - 1][0] == 0);
+	}
+}

test/libsolidity/smtCheckerTests/array_members/push_zero_2d_unsafe.sol

@@ -0,0 +1,10 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[][] a;
+	function f() public {
+		a.push();
+		a[0].push();
+		assert(a[a.length - 1][0] == 100);
+	}
+}

test/libsolidity/smtCheckerTests/array_members/push_zero_safe.sol

@@ -0,0 +1,9 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[] a;
+	function f() public {
+		a.push();
+		assert(a[a.length - 1] == 0);
+	}
+}

test/libsolidity/smtCheckerTests/array_members/push_zero_unsafe.sol

@@ -0,0 +1,9 @@
+pragma experimental SMTChecker;
+
+contract C {
+	uint[] a;
+	function f() public {
+		a.push();
+		assert(a[a.length - 1] == 100);
+	}
+}