Clean up remaining executable_semantics clang-tidy warnings (#906)

Co-authored-by: Geoff Romer <gromer@google.com>

executable_semantics/ast/declaration.h

@@ -6,6 +6,7 @@
 #define EXECUTABLE_SEMANTICS_AST_DECLARATION_H_
 
 #include <string>
+#include <utility>
 #include <vector>
 
 #include "common/ostream.h"
@@ -38,7 +39,7 @@ class Declaration {
   };
 
   Declaration(const Member&) = delete;
-  Declaration& operator=(const Member&) = delete;
+  auto operator=(const Member&) -> Declaration& = delete;
 
   void Print(llvm::raw_ostream& out) const;
   LLVM_DUMP_METHOD void Dump() const { Print(llvm::errs()); }
@@ -152,7 +153,7 @@ class ChoiceDeclaration : public Declaration {
   class Alternative {
    public:
     Alternative(std::string name, Nonnull<Expression*> signature)
-        : name_(name), signature_(signature) {}
+        : name_(std::move(name)), signature_(signature) {}
 
     auto name() const -> const std::string& { return name_; }
     auto signature() const -> const Expression& { return *signature_; }

executable_semantics/ast/member.h

@@ -28,7 +28,7 @@ class Member {
   enum class Kind { FieldMember };
 
   Member(const Member&) = delete;
-  Member& operator=(const Member&) = delete;
+  auto operator=(const Member&) -> Member& = delete;
 
   void Print(llvm::raw_ostream& out) const;
   LLVM_DUMP_METHOD void Dump() const { Print(llvm::errs()); }

executable_semantics/ast/pattern.h

@@ -37,7 +37,7 @@ class Pattern {
   };
 
   Pattern(const Pattern&) = delete;
-  Pattern& operator=(const Pattern&) = delete;
+  auto operator=(const Pattern&) -> Pattern& = delete;
 
   void Print(llvm::raw_ostream& out) const;
   LLVM_DUMP_METHOD void Dump() const { Print(llvm::errs()); }
@@ -206,7 +206,7 @@ class AlternativePattern : public Pattern {
 // expression.
 class ExpressionPattern : public Pattern {
  public:
-  ExpressionPattern(Nonnull<Expression*> expression)
+  explicit ExpressionPattern(Nonnull<Expression*> expression)
       : Pattern(Kind::ExpressionPattern, expression->source_loc()),
         expression_(expression) {}
 

executable_semantics/ast/source_location.h

@@ -26,7 +26,7 @@ class SourceLocation {
   auto operator=(const SourceLocation&) -> SourceLocation& = default;
   auto operator=(SourceLocation&&) -> SourceLocation& = default;
 
-  bool operator==(SourceLocation other) const {
+  auto operator==(SourceLocation other) const -> bool {
     return filename_ == other.filename_ && line_num_ == other.line_num_;
   }