Merge pull request #6028 from ethereum/warn-about-unused-struct-array-expr

Detect custom type expressions that have no effect

Changelog.md

@@ -4,6 +4,7 @@ Language Features:
 
 
 Compiler Features:
+ * Static Analyzer: Warn about expressions with custom types when they have no effect.
 
 
 Bugfixes:

libsolidity/analysis/TypeChecker.cpp

@@ -2320,8 +2320,13 @@ bool TypeChecker::visit(Identifier const& _identifier)
 	if (auto variableDeclaration = dynamic_cast<VariableDeclaration const*>(annotation.referencedDeclaration))
 		annotation.isPure = annotation.isConstant = variableDeclaration->isConstant();
 	else if (dynamic_cast<MagicVariableDeclaration const*>(annotation.referencedDeclaration))
+	{
 		if (dynamic_cast<FunctionType const*>(annotation.type.get()))
 			annotation.isPure = true;
+	}
+	else if (dynamic_cast<TypeType const*>(annotation.type.get()))
+		annotation.isPure = true;
+
 
 	// Check for deprecated function names.
 	// The check is done here for the case without an actual function call.

test/libsolidity/syntaxTests/metaTypes/typeOfContract.sol

@@ -4,3 +4,4 @@ contract Test {
     }
 }
 // ----
+// Warning: (78-88): Statement has no effect.

test/libsolidity/syntaxTests/nameAndTypeResolution/001_name_references.sol

@@ -2,3 +2,5 @@ contract test {
     uint256 variable;
     function f(uint256) public returns (uint out) { f(variable); test; out; }
 }
+// ----
+// Warning: (103-107): Statement has no effect.

test/libsolidity/syntaxTests/nameAndTypeResolution/no_effect_statements.sol

@@ -0,0 +1,16 @@
+contract test {
+ struct s { uint a; uint b;}
+    function f() pure public returns (byte) {
+		s;
+		s(1,2);
+		s[7];
+		uint;
+		uint[7];
+    }
+}
+// ----
+// Warning: (93-94): Statement has no effect.
+// Warning: (98-104): Statement has no effect.
+// Warning: (108-112): Statement has no effect.
+// Warning: (116-120): Statement has no effect.
+// Warning: (124-131): Statement has no effect.