clang-tidy pass on executable_semantics (#963)

executable_semantics/interpreter/action.h

@@ -209,7 +209,7 @@ class StatementAction : public Action {
 // with AST nodes.
 class ScopeAction : public Action {
  public:
-  ScopeAction(Scope scope) : Action(Kind::ScopeAction) {
+  explicit ScopeAction(Scope scope) : Action(Kind::ScopeAction) {
     StartScope(std::move(scope));
   }
 

executable_semantics/interpreter/address.h

@@ -36,7 +36,7 @@ class AllocationId {
   // details of Heap.
   friend class Heap;
 
-  AllocationId(size_t index) : index_(index) {}
+  explicit AllocationId(size_t index) : index_(index) {}
 
   size_t index_;
 };

executable_semantics/interpreter/resolve_names.cpp

@@ -113,8 +113,7 @@ void PopulateNamesInStatement(Arena* arena,
 
 // Populates names for a member. See PopulateNamesInDeclaration for overall
 // flow.
-void PopulateNamesInMember(Arena* arena, const Member& member,
-                           StaticScope& static_scope) {
+void PopulateNamesInMember(const Member& member, StaticScope& static_scope) {
   switch (member.kind()) {
     case MemberKind::FieldMember: {
       const auto& field = cast<FieldMember>(member);
@@ -148,7 +147,7 @@ void PopulateNamesInDeclaration(Arena* arena, Declaration& declaration,
       class_decl.static_scope().AddParent(&static_scope);
       static_scope.Add(class_decl.name(), &declaration);
       for (auto* member : class_decl.members()) {
-        PopulateNamesInMember(arena, *member, class_decl.static_scope());
+        PopulateNamesInMember(*member, class_decl.static_scope());
       }
       break;
     }

executable_semantics/interpreter/value.h

@@ -117,7 +117,7 @@ class IntValue : public Value {
 // A function value.
 class FunctionValue : public Value {
  public:
-  FunctionValue(Nonnull<const FunctionDeclaration*> declaration)
+  explicit FunctionValue(Nonnull<const FunctionDeclaration*> declaration)
       : Value(Kind::FunctionValue), declaration_(declaration) {}
 
   static auto classof(const Value* value) -> bool {
@@ -495,7 +495,7 @@ class ContinuationValue : public Value {
     ~StackFragment();
 
     StackFragment(StackFragment&&) = delete;
-    StackFragment& operator=(StackFragment&&) = delete;
+    auto operator=(StackFragment&&) -> StackFragment& = delete;
 
     // Store the given partial todo stack in *this, which must currently be
     // empty. The stack is represented with the top of the stack at the