Generic classes (#1124)

* start of generic classes

* fix regressions

* class functions in interfaces

* access to class function on interface from class parameter

* more stuff working for generic classes

* fixing bugs

* update TypeEqual for generic classes

* fixing bugs and finding new ones

* disable unqualified access to members from other members for now

* minor edits

* bug fixes

* introduce compile_time_value to use in type checker instead of constant_value

* cleanup

* put a CHECK back in

* failure test cases for the new FATAL_COMPILATION_ERROR

* change a runtime FATAL into a FATAL_COMPILATION_ERROR

* Update executable_semantics/ast/declaration.h

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/action_stack.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/interpreter.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/value.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/value.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/interpreter.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/value.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/value.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/resolve_names.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/type_checker.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/type_checker.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/type_checker.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* responses to reviews

* Update executable_semantics/interpreter/type_checker.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* rename compile_time_value to symbolic_identity

* Update executable_semantics/interpreter/type_checker.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/type_checker.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/type_checker.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/type_checker.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/type_checker.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/type_checker.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/value.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/value.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* Update executable_semantics/interpreter/value.cpp

Co-authored-by: Jon Meow <jperkins@google.com>

* more edits from review

* Apply suggestions from code review

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

* review responses

* Update executable_semantics/interpreter/interpreter.cpp

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

* const impl_scope for TypeCheckChoiceDeclaration

* add some const

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

executable_semantics/ast/expression.h

@@ -5,6 +5,7 @@
 #ifndef EXECUTABLE_SEMANTICS_AST_EXPRESSION_H_
 #define EXECUTABLE_SEMANTICS_AST_EXPRESSION_H_
 
+#include <map>
 #include <optional>
 #include <string>
 #include <variant>
@@ -12,7 +13,6 @@
 
 #include "common/ostream.h"
 #include "executable_semantics/ast/ast_node.h"
-#include "executable_semantics/ast/generic_binding.h"
 #include "executable_semantics/ast/paren_contents.h"
 #include "executable_semantics/ast/source_location.h"
 #include "executable_semantics/ast/static_scope.h"
@@ -25,12 +25,14 @@ namespace Carbon {
 
 class Value;
 class VariableType;
+class ImplBinding;
 
 class Expression : public AstNode {
  public:
   ~Expression() override = 0;
 
   void Print(llvm::raw_ostream& out) const override;
+  void PrintID(llvm::raw_ostream& out) const override;
 
   static auto classof(const AstNode* node) {
     return InheritsFromExpression(node->kind());
@@ -43,7 +45,10 @@ class Expression : public AstNode {
   }
 
   // The static type of this expression. Cannot be called before typechecking.
-  auto static_type() const -> const Value& { return **static_type_; }
+  auto static_type() const -> const Value& {
+    CHECK(static_type_.has_value());
+    return **static_type_;
+  }
 
   // Sets the static type of this expression. Can only be called once, during
   // typechecking.
@@ -354,7 +359,10 @@ class PrimitiveOperatorExpression : public Expression {
   std::vector<Nonnull<Expression*>> arguments_;
 };
 
-class ImplBinding;
+class GenericBinding;
+
+using BindingMap =
+    std::map<Nonnull<const GenericBinding*>, Nonnull<const Value*>>;
 
 class CallExpression : public Expression {
  public:
@@ -390,10 +398,17 @@ class CallExpression : public Expression {
     impls_ = impls;
   }
 
+  auto deduced_args() const -> const BindingMap& { return deduced_args_; }
+
+  void set_deduced_args(const BindingMap& deduced_args) {
+    deduced_args_ = deduced_args;
+  }
+
  private:
   Nonnull<Expression*> function_;
   Nonnull<Expression*> argument_;
   std::map<Nonnull<const ImplBinding*>, ValueNodeView> impls_;
+  BindingMap deduced_args_;
 };
 
 class FunctionTypeLiteral : public Expression {