Constants are considered pure.

Changelog.md

@@ -30,6 +30,7 @@ Compiler Features:
 Bugfixes:
  * NatSpec: Constructors and functions have consistent userdoc output.
  * Inheritance: Disallow public state variables overwriting ``pure`` functions.
+ * State Mutability: Constant public state variables are considered ``pure`` functions.
 
 
 ### 0.6.12 (unreleased)

libsolidity/analysis/OverrideChecker.cpp

@@ -289,7 +289,7 @@ StateMutability OverrideProxy::stateMutability() const
 	return std::visit(GenericVisitor{
 		[&](FunctionDefinition const* _item) { return _item->stateMutability(); },
 		[&](ModifierDefinition const*) { solAssert(false, "Requested state mutability from modifier."); return StateMutability{}; },
-		[&](VariableDeclaration const*) { return StateMutability::View; }
+		[&](VariableDeclaration const* _var) { return _var->isConstant() ? StateMutability::Pure : StateMutability::View; }
 	}, m_item);
 }
 

test/libsolidity/syntaxTests/inheritance/override/public_constant_var_overrides_pure.sol

@@ -0,0 +1,7 @@
+abstract contract C {
+    function foo() external pure virtual returns (uint);
+}
+contract X is C {
+	uint public constant override foo = 7;
+}
+// ----

test/libsolidity/syntaxTests/inheritance/override/public_immutable_var_overrides_pure.sol

@@ -0,0 +1,8 @@
+abstract contract C {
+    function foo() external pure virtual returns (uint);
+}
+contract X is C {
+	uint public immutable override foo = 7;
+}
+// ----
+// TypeError 6959: (100-124): Overriding public state variable changes state mutability from "pure" to "view".