Deprecate use of unary '+'

The unary '+' serves no meaningful purpose in Solidity and it makes it
possible to produce typos with dagerous implications (e.g. 'a =+5 '),
so we are deprecating it.  The SyntaxChecker currently issues warnings
on the unary '+' but will still compile it for now.

2 files changed, 23 insertions, 0 deletions

diff --git a/libsolidity/analysis/SyntaxChecker.cpp b/libsolidity/analysis/SyntaxChecker.cpp
index 89014133..308733df 100644
--- a/libsolidity/analysis/SyntaxChecker.cpp
+++ b/libsolidity/analysis/SyntaxChecker.cpp
@@ -32,6 +32,16 @@ bool SyntaxChecker::checkSyntax(ASTNode const& _astRoot)
 	return Error::containsOnlyWarnings(m_errors);
 }
 
+void SyntaxChecker::warning(SourceLocation const& _location, string const& _description)
+{
+	auto err = make_shared<Error>(Error::Type::Warning);
+	*err <<
+		errinfo_sourceLocation(_location) <<
+		errinfo_comment(_description);
+
+	m_errors.push_back(err);
+}
+
 void SyntaxChecker::syntaxError(SourceLocation const& _location, std::string const& _description)
 {
 	auto err = make_shared<Error>(Error::Type::SyntaxError);
@@ -148,6 +158,15 @@ bool SyntaxChecker::visit(Break const& _breakStatement)
 	return true;
 }
 
+bool SyntaxChecker::visit(UnaryOperation const& _operation)
+{
+	if (_operation.getOperator() == Token::Add)
+	{
+		warning(_operation.location(), "Use of unary + is deprecated");
+	}
+	return true;
+}
+
 bool SyntaxChecker::visit(PlaceholderStatement const&)
 {
 	m_placeholderFound = true;
diff --git a/libsolidity/analysis/SyntaxChecker.h b/libsolidity/analysis/SyntaxChecker.h
index 308e128b..8d7dcdd3 100644
--- a/libsolidity/analysis/SyntaxChecker.h
+++ b/libsolidity/analysis/SyntaxChecker.h
@@ -32,6 +32,7 @@ namespace solidity
  * The module that performs syntax analysis on the AST:
  *  - whether continue/break is in a for/while loop.
  *  - whether a modifier contains at least one '_'
+ *  - issues deprecation warnings for unary '+'
  */
 class SyntaxChecker: private ASTConstVisitor
 {
@@ -43,6 +44,7 @@ public:
 
 private:
 	/// Adds a new error to the list of errors.
+	void warning(SourceLocation const& _location, std::string const& _description);
 	void syntaxError(SourceLocation const& _location, std::string const& _description);
 
 	virtual bool visit(SourceUnit const& _sourceUnit) override;
@@ -60,6 +62,8 @@ private:
 	virtual bool visit(Continue const& _continueStatement) override;
 	virtual bool visit(Break const& _breakStatement) override;
 
+	virtual bool visit(UnaryOperation const& _operation) override;
+
 	virtual bool visit(PlaceholderStatement const& _placeholderStatement) override;
 
 	ErrorList& m_errors;