From d3647b13e4362a17e72fe6d36b53f152230d77d4 Mon Sep 17 00:00:00 2001
From: chriseth <chris@ethereum.org>
Date: Tue, 14 Jul 2020 20:11:01 +0200
Subject: [PATCH] Disallow public state variables overriding pure functions.

---
 Changelog.md                                  |  1 +
 docs/contracts/inheritance.rst                |  2 +-
 libsolidity/analysis/OverrideChecker.cpp      | 52 +++++++++----------
 .../override/public_var_overrides_pure.sol    |  8 +++
 4 files changed, 36 insertions(+), 27 deletions(-)
 create mode 100644 test/libsolidity/syntaxTests/inheritance/override/public_var_overrides_pure.sol

diff --git a/Changelog.md b/Changelog.md
index 1195fee1a..c2aa865bc 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -29,6 +29,7 @@ Compiler Features:
 
 Bugfixes:
  * NatSpec: Constructors and functions have consistent userdoc output.
+ * Inheritance: Disallow public state variables overwriting ``pure`` functions.
 
 
 ### 0.6.12 (unreleased)
diff --git a/docs/contracts/inheritance.rst b/docs/contracts/inheritance.rst
index 343604a34..f628d49fb 100644
--- a/docs/contracts/inheritance.rst
+++ b/docs/contracts/inheritance.rst
@@ -310,7 +310,7 @@ of the variable:
 
     contract A
     {
-        function f() external pure virtual returns(uint) { return 5; }
+        function f() external view virtual returns(uint) { return 5; }
     }
 
     contract B is A
diff --git a/libsolidity/analysis/OverrideChecker.cpp b/libsolidity/analysis/OverrideChecker.cpp
index c58fd2c85..b5fe33ade 100644
--- a/libsolidity/analysis/OverrideChecker.cpp
+++ b/libsolidity/analysis/OverrideChecker.cpp
@@ -584,35 +584,35 @@ void OverrideChecker::checkOverride(OverrideProxy const& _overriding, OverridePr
 				"Overridden " + _overriding.astNodeName() + " is here:"
 			);
 
-		// This is only relevant for a function overriding a function.
-		if (_overriding.isFunction())
-		{
-			// Stricter mutability is always okay except when super is Payable
-			if ((
+		// Stricter mutability is always okay except when super is Payable
+		if (
+			(_overriding.isFunction() || _overriding.isVariable()) &&
+			(
 				_overriding.stateMutability() > _super.stateMutability() ||
 				_super.stateMutability() == StateMutability::Payable
-				) &&
-				_overriding.stateMutability() != _super.stateMutability()
-			)
-				overrideError(
-					_overriding,
-					_super,
-					6959_error,
-					"Overriding function changes state mutability from \"" +
-					stateMutabilityToString(_super.stateMutability()) +
-					"\" to \"" +
-					stateMutabilityToString(_overriding.stateMutability()) +
-					"\"."
-				);
+			) &&
+			_overriding.stateMutability() != _super.stateMutability()
+		)
+			overrideError(
+				_overriding,
+				_super,
+				6959_error,
+				"Overriding " +
+				_overriding.astNodeName() +
+				" changes state mutability from \"" +
+				stateMutabilityToString(_super.stateMutability()) +
+				"\" to \"" +
+				stateMutabilityToString(_overriding.stateMutability()) +
+				"\"."
+			);
 
-			if (_overriding.unimplemented() && !_super.unimplemented())
-				overrideError(
-					_overriding,
-					_super,
-					4593_error,
-					"Overriding an implemented function with an unimplemented function is not allowed."
-				);
-		}
+		if (_overriding.unimplemented() && !_super.unimplemented())
+			overrideError(
+				_overriding,
+				_super,
+				4593_error,
+				"Overriding an implemented function with an unimplemented function is not allowed."
+			);
 	}
 }
 
diff --git a/test/libsolidity/syntaxTests/inheritance/override/public_var_overrides_pure.sol b/test/libsolidity/syntaxTests/inheritance/override/public_var_overrides_pure.sol
new file mode 100644
index 000000000..835351b3d
--- /dev/null
+++ b/test/libsolidity/syntaxTests/inheritance/override/public_var_overrides_pure.sol
@@ -0,0 +1,8 @@
+abstract contract C {
+    function foo() external pure virtual returns (uint);
+}
+contract X is C {
+	uint public override foo;
+}
+// ----
+// TypeError 6959: (100-124): Overriding public state variable changes state mutability from "pure" to "view".