Add a code generator for enum boilerplate (#401)

Go does not have enums, but they are quite useful, so we emulate them
with int-kinded types and use switches and whatnot to convert them to
and from strings.

There are enough of these in the new compiler stack at this point that
maintaining all of these stringification functions is getting tedious
and error-prone, so this PR contains a very simple, 200-line
`//go:generate` helper for generating those functions.

I surveyed other existing packages of this kind, but unfortunately they
all want to put varying strong constraints on how we organize and name
our "enums", so I felt that we should just write the simplest possible
thing to fit our use-case.

Author: mcy

experimental/ast/decl.go

@@ -22,21 +22,6 @@ import (
 	"github.com/bufbuild/protocompile/internal/arena"
 )
 
-const (
-	DeclKindInvalid DeclKind = iota
-	DeclKindEmpty
-	DeclKindSyntax
-	DeclKindPackage
-	DeclKindImport
-	DeclKindDef
-	DeclKindBody
-	DeclKindRange
-)
-
-// DeclKind is a kind of declaration. There is one value of DeclKind for each
-// Decl* type in this package.
-type DeclKind int8
-
 // DeclAny is any Decl* type in this package.
 //
 // Values of this type can be obtained by calling an AsAny method on a Decl*

experimental/ast/decl_def.go

@@ -20,25 +20,6 @@ import (
 	"github.com/bufbuild/protocompile/internal/arena"
 )
 
-const (
-	DefKindInvalid DefKind = iota
-	DefKindMessage
-	DefKindEnum
-	DefKindService
-	DefKindExtend
-	DefKindField
-	DefKindOneof
-	DefKindGroup
-	DefKindEnumValue
-	DefKindMethod
-	DefKindOption
-)
-
-// DefKind is the kind of definition a [DeclDef] contains.
-//
-// See [DeclDef.Classify].
-type DefKind int8
-
 // DeclDef is a general Protobuf definition.
 //
 // This [Decl] represents the union of several similar AST nodes, to aid in permissive

experimental/ast/doc.go

@@ -92,3 +92,5 @@
 // library. Outside of this file, documentation is written assuming this has
 // already happened.
 package ast
+
+//go:generate go run github.com/bufbuild/protocompile/internal/enum enums.yaml