Merge pull request #4139 from ethereum/abiEncodeIsPure

ABI encoding functions are pure and should be usable in constants.

5 files changed, 18 insertions, 3 deletions

diff --git a/Changelog.md b/Changelog.md
index ddd33df7..d6f54070 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -19,6 +19,7 @@ Bugfixes:
  * Code Generator: Fix ``revert`` with reason coming from a state or local string variable.
  * Type Checker: Show proper error when trying to ``emit`` a non-event.
  * Type Checker: Warn about empty tuple components (this will turn into an error with version 0.5.0).
+ * Type Checker: The ABI encoding functions are pure and thus can be used for constants.
 
 ### 0.4.23 (2018-04-19)
 
diff --git a/libsolidity/analysis/TypeChecker.cpp b/libsolidity/analysis/TypeChecker.cpp
index a222bdf0..e8694e88 100644
--- a/libsolidity/analysis/TypeChecker.cpp
+++ b/libsolidity/analysis/TypeChecker.cpp
@@ -2093,6 +2093,9 @@ bool TypeChecker::visit(MemberAccess const& _memberAccess)
 	if (auto tt = dynamic_cast<TypeType const*>(exprType.get()))
 		if (tt->actualType()->category() == Type::Category::Enum)
 			annotation.isPure = true;
+	if (auto magicType = dynamic_cast<MagicType const*>(exprType.get()))
+		if (magicType->kind() == MagicType::Kind::ABI)
+			annotation.isPure = true;
 
 	return false;
 }
diff --git a/libsolidity/ast/Types.cpp b/libsolidity/ast/Types.cpp
index dc548538..60e3183c 100644
--- a/libsolidity/ast/Types.cpp
+++ b/libsolidity/ast/Types.cpp
@@ -2865,7 +2865,11 @@ bool FunctionType::isPure() const
 		m_kind == Kind::RIPEMD160 ||
 		m_kind == Kind::AddMod ||
 		m_kind == Kind::MulMod ||
-		m_kind == Kind::ObjectCreation;
+		m_kind == Kind::ObjectCreation ||
+		m_kind == Kind::ABIEncode ||
+		m_kind == Kind::ABIEncodePacked ||
+		m_kind == Kind::ABIEncodeWithSelector ||
+		m_kind == Kind::ABIEncodeWithSignature;
 }
 
 TypePointers FunctionType::parseElementaryTypeVector(strings const& _types)
diff --git a/libsolidity/ast/Types.h b/libsolidity/ast/Types.h
index 6defacfc..4884696d 100644
--- a/libsolidity/ast/Types.h
+++ b/libsolidity/ast/Types.h
@@ -1046,8 +1046,8 @@ public:
 		return *m_declaration;
 	}
 	bool hasDeclaration() const { return !!m_declaration; }
-	/// @returns true if the result of this function only depends on its arguments
-	/// and it does not modify the state.
+	/// @returns true if the result of this function only depends on its arguments,
+	/// does not modify the state and is a compile-time constant.
 	/// Currently, this will only return true for internal functions like keccak and ecrecover.
 	bool isPure() const;
 	bool isPayable() const { return m_stateMutability == StateMutability::Payable; }
diff --git a/test/libsolidity/syntaxTests/constants/abi_encoding_constant.sol b/test/libsolidity/syntaxTests/constants/abi_encoding_constant.sol
new file mode 100644
index 00000000..dd6968a0
--- /dev/null
+++ b/test/libsolidity/syntaxTests/constants/abi_encoding_constant.sol
@@ -0,0 +1,7 @@
+contract C {
+    bytes32 constant a = keccak256(abi.encode(1, 2));
+    bytes32 constant b = keccak256(abi.encodePacked(uint(1), a));
+    bytes32 constant c = keccak256(abi.encodeWithSelector(0x12345678, b, 2));
+    bytes32 constant d = keccak256(abi.encodeWithSignature("f()", 1, 2));
+}
+// ----