chore: Add generics to typescript generator (#4664)

* feat: Support generating generics in interfaces
* Switch struct to a template
* Support generics in apitypings

coderd/util/slice/slice.go

@@ -22,6 +22,21 @@ func Overlap[T comparable](a []T, b []T) bool {
 	})
 }
 
+// Unique returns a new slice with all duplicate elements removed.
+// This is a slow function on large lists.
+// TODO: Sort elements and implement a faster search algorithm if we
+// really start to use this.
+func Unique[T comparable](a []T) []T {
+	cpy := make([]T, 0, len(a))
+	for _, v := range a {
+		v := v
+		if !Contains(cpy, v) {
+			cpy = append(cpy, v)
+		}
+	}
+	return cpy
+}
+
 func OverlapCompare[T any](a []T, b []T, equal func(a, b T) bool) bool {
 	// For each element in b, if at least 1 is contained in 'a',
 	// return true.

coderd/util/slice/slice_test.go

@@ -9,6 +9,22 @@ import (
 	"github.com/coder/coder/coderd/util/slice"
 )
 
+func TestUnique(t *testing.T) {
+	t.Parallel()
+
+	require.ElementsMatch(t,
+		[]int{1, 2, 3, 4, 5},
+		slice.Unique([]int{
+			1, 2, 3, 4, 5, 1, 2, 3, 4, 5,
+		}))
+
+	require.ElementsMatch(t,
+		[]string{"a"},
+		slice.Unique([]string{
+			"a", "a", "a",
+		}))
+}
+
 func TestContains(t *testing.T) {
 	t.Parallel()
 

scripts/apitypings/main.go

@@ -1,15 +1,18 @@
 package main
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"go/types"
 	"os"
+	"path"
 	"path/filepath"
 	"reflect"
 	"regexp"
 	"sort"
 	"strings"
+	"text/template"
 
 	"github.com/fatih/structtag"
 	"golang.org/x/tools/go/packages"
@@ -17,6 +20,7 @@ import (
 
 	"cdr.dev/slog"
 	"cdr.dev/slog/sloggers/sloghuman"
+	"github.com/coder/coder/coderd/util/slice"
 )
 
 const (
@@ -27,13 +31,25 @@ const (
 func main() {
 	ctx := context.Background()
 	log := slog.Make(sloghuman.Sink(os.Stderr))
-	codeBlocks, err := GenerateFromDirectory(ctx, log, baseDir)
+	output, err := Generate(baseDir)
 	if err != nil {
 		log.Fatal(ctx, err.Error())
 	}
 
 	// Just cat the output to a file to capture it
-	_, _ = fmt.Println(codeBlocks.String())
+	fmt.Println(output)
+}
+
+func Generate(directory string) (string, error) {
+	ctx := context.Background()
+	log := slog.Make(sloghuman.Sink(os.Stderr))
+	codeBlocks, err := GenerateFromDirectory(ctx, log, directory)
+	if err != nil {
+		return "", err
+	}
+
+	// Just cat the output to a file to capture it
+	return codeBlocks.String(), nil
 }
 
 // TypescriptTypes holds all the code blocks created.
@@ -41,6 +57,7 @@ type TypescriptTypes struct {
 	// Each entry is the type name, and it's typescript code block.
 	Types    map[string]string
 	Enums    map[string]string
+	Generics map[string]string
 }
 
 // String just combines all the codeblocks.
@@ -50,6 +67,7 @@ func (t TypescriptTypes) String() string {
 
 	sortedTypes := make([]string, 0, len(t.Types))
 	sortedEnums := make([]string, 0, len(t.Enums))
+	sortedGenerics := make([]string, 0, len(t.Generics))
 
 	for k := range t.Types {
 		sortedTypes = append(sortedTypes, k)
@@ -57,9 +75,13 @@ func (t TypescriptTypes) String() string {
 	for k := range t.Enums {
 		sortedEnums = append(sortedEnums, k)
 	}
+	for k := range t.Generics {
+		sortedGenerics = append(sortedGenerics, k)
+	}
 
 	sort.Strings(sortedTypes)
 	sort.Strings(sortedEnums)
+	sort.Strings(sortedGenerics)
 
 	for _, k := range sortedTypes {
 		v := t.Types[k]
@@ -73,6 +95,12 @@ func (t TypescriptTypes) String() string {
 		_, _ = s.WriteRune('\n')
 	}
 
+	for _, k := range sortedGenerics {
+		v := t.Generics[k]
+		_, _ = s.WriteString(v)
+		_, _ = s.WriteRune('\n')
+	}
+
 	return strings.TrimRight(s.String(), "\n")
 }
 
@@ -80,6 +108,7 @@ func (t TypescriptTypes) String() string {
 func GenerateFromDirectory(ctx context.Context, log slog.Logger, directory string) (*TypescriptTypes, error) {
 	g := Generator{
 		log:      log,
+		builtins: make(map[string]string),
 	}
 	err := g.parsePackage(ctx, directory)
 	if err != nil {
@@ -98,6 +127,15 @@ type Generator struct {
 	// Package we are scanning.
 	pkg *packages.Package
 	log slog.Logger
+
+	// builtins is kinda a hack to get around the fact that using builtin
+	// generic constraints is common. We want to support them even though
+	// they are external to our package.
+	// It is also a string because the builtins are not proper go types. Meaning
+	// if you inspect the types, they are not "correct". Things like "comparable"
+	// cannot be implemented in go. So they are a first class thing that we just
+	// have to make a static string for ¯\_(ツ)_/¯
+	builtins map[string]string
 }
 
 // parsePackage takes a list of patterns such as a directory, and parses them.
@@ -128,12 +166,15 @@ func (g *Generator) parsePackage(ctx context.Context, patterns ...string) error
 
 // generateAll will generate for all types found in the pkg
 func (g *Generator) generateAll() (*TypescriptTypes, error) {
-	structs := make(map[string]string)
-	enums := make(map[string]types.Object)
-	enumConsts := make(map[string][]*types.Const)
+	m := &Maps{
+		Structs:      make(map[string]string),
+		Generics:     make(map[string]string),
+		Enums:        make(map[string]types.Object),
+		EnumConsts:   make(map[string][]*types.Const),
+		IgnoredTypes: make(map[string]struct{}),
+	}
 
 	// Look for comments that indicate to ignore a type for typescript generation.
-	ignoredTypes := make(map[string]struct{})
 	ignoreRegex := regexp.MustCompile("@typescript-ignore[:]?(?P<ignored_types>.*)")
 	for _, file := range g.pkg.Syntax {
 		for _, comment := range file.Comments {
@@ -144,7 +185,7 @@ func (g *Generator) generateAll() (*TypescriptTypes, error) {
 				if len(matches) >= ignored && matches[ignored] != "" {
 					arr := strings.Split(matches[ignored], ",")
 					for _, s := range arr {
-						ignoredTypes[strings.TrimSpace(s)] = struct{}{}
+						m.IgnoredTypes[strings.TrimSpace(s)] = struct{}{}
 					}
 				}
 			}
@@ -153,80 +194,24 @@ func (g *Generator) generateAll() (*TypescriptTypes, error) {
 
 	for _, n := range g.pkg.Types.Scope().Names() {
 		obj := g.pkg.Types.Scope().Lookup(n)
-		if obj == nil || obj.Type() == nil {
-			// This would be weird, but it is if the package does not have the type def.
-			continue
-		}
-
-		// Exclude ignored types
-		if _, ok := ignoredTypes[obj.Name()]; ok {
-			continue
-		}
-
-		switch obj := obj.(type) {
-		// All named types are type declarations
-		case *types.TypeName:
-			named, ok := obj.Type().(*types.Named)
-			if !ok {
-				panic("all typename should be named types")
-			}
-			switch named.Underlying().(type) {
-			case *types.Struct:
-				// type <Name> struct
-				// Structs are obvious.
-				st, _ := obj.Type().Underlying().(*types.Struct)
-				codeBlock, err := g.buildStruct(obj, st)
+		err := g.generateOne(m, obj)
 		if err != nil {
-					return nil, xerrors.Errorf("generate %q: %w", obj.Name(), err)
+			return nil, xerrors.Errorf("%q: %w", n, err)
 		}
-				structs[obj.Name()] = codeBlock
-			case *types.Basic:
-				// type <Name> string
-				// These are enums. Store to expand later.
-				enums[obj.Name()] = obj
-			case *types.Map:
-				// Declared maps that are not structs are still valid codersdk objects.
-				// Handle them custom by calling 'typescriptType' directly instead of
-				// iterating through each struct field.
-				// These types support no json/typescript tags.
-				// These are **NOT** enums, as a map in Go would never be used for an enum.
-				ts, err := g.typescriptType(obj.Type().Underlying())
-				if err != nil {
-					return nil, xerrors.Errorf("(map) generate %q: %w", obj.Name(), err)
 	}
 
-				var str strings.Builder
-				_, _ = str.WriteString(g.posLine(obj))
-				if ts.AboveTypeLine != "" {
-					str.WriteString(ts.AboveTypeLine)
-					str.WriteRune('\n')
-				}
-				// Use similar output syntax to enums.
-				str.WriteString(fmt.Sprintf("export type %s = %s\n", obj.Name(), ts.ValueType))
-				structs[obj.Name()] = str.String()
-			case *types.Array, *types.Slice:
-				// TODO: @emyrk if you need this, follow the same design as "*types.Map" case.
-			}
-		case *types.Var:
-			// TODO: Are any enums var declarations? This is also codersdk.Me.
-		case *types.Const:
-			// We only care about named constant types, since they are enums
-			if named, ok := obj.Type().(*types.Named); ok {
-				name := named.Obj().Name()
-				enumConsts[name] = append(enumConsts[name], obj)
-			}
-		case *types.Func:
-			// Noop
-		default:
-			fmt.Println(obj.Name())
+	// Add the builtins
+	for n, value := range g.builtins {
+		if value != "" {
+			m.Generics[n] = value
 		}
 	}
 
 	// Write all enums
 	enumCodeBlocks := make(map[string]string)
-	for name, v := range enums {
+	for name, v := range m.Enums {
 		var values []string
-		for _, elem := range enumConsts[name] {
+		for _, elem := range m.EnumConsts[name] {
 			// TODO: If we have non string constants, we need to handle that
 			//		here.
 			values = append(values, elem.Val().String())
@@ -242,21 +227,182 @@ func (g *Generator) generateAll() (*TypescriptTypes, error) {
 	}
 
 	return &TypescriptTypes{
-		Types: structs,
+		Types:    m.Structs,
 		Enums:    enumCodeBlocks,
+		Generics: m.Generics,
 	}, nil
 }
 
+type Maps struct {
+	Structs      map[string]string
+	Generics     map[string]string
+	Enums        map[string]types.Object
+	EnumConsts   map[string][]*types.Const
+	IgnoredTypes map[string]struct{}
+}
+
+func (g *Generator) generateOne(m *Maps, obj types.Object) error {
+	if obj == nil || obj.Type() == nil {
+		// This would be weird, but it is if the package does not have the type def.
+		return nil
+	}
+
+	// Exclude ignored types
+	if _, ok := m.IgnoredTypes[obj.Name()]; ok {
+		return nil
+	}
+
+	switch obj := obj.(type) {
+	// All named types are type declarations
+	case *types.TypeName:
+		named, ok := obj.Type().(*types.Named)
+		if !ok {
+			panic("all typename should be named types")
+		}
+		switch underNamed := named.Underlying().(type) {
+		case *types.Struct:
+			// type <Name> struct
+			// Structs are obvious.
+			codeBlock, err := g.buildStruct(obj, underNamed)
+			if err != nil {
+				return xerrors.Errorf("generate %q: %w", obj.Name(), err)
+			}
+			m.Structs[obj.Name()] = codeBlock
+		case *types.Basic:
+			// type <Name> string
+			// These are enums. Store to expand later.
+			m.Enums[obj.Name()] = obj
+		case *types.Map:
+			// Declared maps that are not structs are still valid codersdk objects.
+			// Handle them custom by calling 'typescriptType' directly instead of
+			// iterating through each struct field.
+			// These types support no json/typescript tags.
+			// These are **NOT** enums, as a map in Go would never be used for an enum.
+			ts, err := g.typescriptType(obj.Type().Underlying())
+			if err != nil {
+				return xerrors.Errorf("(map) generate %q: %w", obj.Name(), err)
+			}
+
+			var str strings.Builder
+			_, _ = str.WriteString(g.posLine(obj))
+			if ts.AboveTypeLine != "" {
+				str.WriteString(ts.AboveTypeLine)
+				str.WriteRune('\n')
+			}
+			// Use similar output syntax to enums.
+			str.WriteString(fmt.Sprintf("export type %s = %s\n", obj.Name(), ts.ValueType))
+			m.Structs[obj.Name()] = str.String()
+		case *types.Array, *types.Slice:
+		// TODO: @emyrk if you need this, follow the same design as "*types.Map" case.
+		case *types.Interface:
+			// Interfaces are used as generics. Non-generic interfaces are
+			// not supported.
+			if underNamed.NumEmbeddeds() == 1 {
+				union, ok := underNamed.EmbeddedType(0).(*types.Union)
+				if !ok {
+					// If the underlying is not a union, but has 1 type. It's
+					// just that one type.
+					union = types.NewUnion([]*types.Term{
+						// Set the tilde to true to support underlying.
+						// Doesn't actually affect our generation.
+						types.NewTerm(true, underNamed.EmbeddedType(0)),
+					})
+				}
+
+				block, err := g.buildUnion(obj, union)
+				if err != nil {
+					return xerrors.Errorf("generate union %q: %w", obj.Name(), err)
+				}
+				m.Generics[obj.Name()] = block
+			}
+		case *types.Signature:
+		// Ignore named functions.
+		default:
+			// If you hit this error, you added a new unsupported named type.
+			// The easiest way to solve this is add a new case above with
+			// your type and a TODO to implement it.
+			return xerrors.Errorf("unsupported named type %q", underNamed.String())
+		}
+	case *types.Var:
+		// TODO: Are any enums var declarations? This is also codersdk.Me.
+	case *types.Const:
+		// We only care about named constant types, since they are enums
+		if named, ok := obj.Type().(*types.Named); ok {
+			name := named.Obj().Name()
+			m.EnumConsts[name] = append(m.EnumConsts[name], obj)
+		}
+	case *types.Func:
+		// Noop
+	default:
+		fmt.Println(obj.Name())
+	}
+	return nil
+}
+
 func (g *Generator) posLine(obj types.Object) string {
 	file := g.pkg.Fset.File(obj.Pos())
-	return fmt.Sprintf("// From %s\n", filepath.Join("codersdk", filepath.Base(file.Name())))
+	// Do not use filepath, as that changes behavior based on OS
+	return fmt.Sprintf("// From %s\n", path.Join("codersdk", filepath.Base(file.Name())))
 }
 
 // buildStruct just prints the typescript def for a type.
-func (g *Generator) buildStruct(obj types.Object, st *types.Struct) (string, error) {
+func (g *Generator) buildUnion(obj types.Object, st *types.Union) (string, error) {
 	var s strings.Builder
 	_, _ = s.WriteString(g.posLine(obj))
-	_, _ = s.WriteString(fmt.Sprintf("export interface %s ", obj.Name()))
+
+	allTypes := make([]string, 0, st.Len())
+	var optional bool
+	for i := 0; i < st.Len(); i++ {
+		term := st.Term(i)
+		scriptType, err := g.typescriptType(term.Type())
+		if err != nil {
+			return "", xerrors.Errorf("union %q for %q failed to get type: %w", st.String(), obj.Name(), err)
+		}
+		allTypes = append(allTypes, scriptType.ValueType)
+		optional = optional || scriptType.Optional
+	}
+
+	if optional {
+		allTypes = append(allTypes, "null")
+	}
+
+	allTypes = slice.Unique(allTypes)
+
+	s.WriteString(fmt.Sprintf("export type %s = %s\n", obj.Name(), strings.Join(allTypes, " | ")))
+
+	return s.String(), nil
+}
+
+type structTemplateState struct {
+	PosLine   string
+	Name      string
+	Fields    []string
+	Generics  []string
+	Extends   string
+	AboveLine string
+}
+
+const structTemplate = `{{ .PosLine -}}
+{{ if .AboveLine }}{{ .AboveLine }}
+{{ end }}export interface {{ .Name }}{{ if .Generics }}<{{ join .Generics ", " }}>{{ end }}{{ if .Extends }} extends {{ .Extends }}{{ end }} {
+{{ join .Fields "\n"}}
+}
+`
+
+// buildStruct just prints the typescript def for a type.
+func (g *Generator) buildStruct(obj types.Object, st *types.Struct) (string, error) {
+	state := structTemplateState{}
+	tpl := template.New("struct")
+	tpl.Funcs(template.FuncMap{
+		"join": strings.Join,
+	})
+	tpl, err := tpl.Parse(structTemplate)
+	if err != nil {
+		return "", xerrors.Errorf("parse struct template: %w", err)
+	}
+
+	state.PosLine = g.posLine(obj)
+	state.Name = obj.Name()
 
 	// Handle named embedded structs in the codersdk package via extension.
 	var extends []string
@@ -272,10 +418,10 @@ func (g *Generator) buildStruct(obj types.Object, st *types.Struct) (string, err
 		}
 	}
 	if len(extends) > 0 {
-		_, _ = s.WriteString(fmt.Sprintf("extends %s ", strings.Join(extends, ", ")))
+		state.Extends = strings.Join(extends, ", ")
 	}
 
-	_, _ = s.WriteString("{\n")
+	genericsUsed := make(map[string]string)
 	// For each field in the struct, we print 1 line of the typescript interface
 	for i := 0; i < st.NumFields(); i++ {
 		if extendedFields[i] {
@@ -330,21 +476,109 @@ func (g *Generator) buildStruct(obj types.Object, st *types.Struct) (string, err
 			}
 		}
 
-		if tsType.AboveTypeLine != "" {
-			_, _ = s.WriteString(tsType.AboveTypeLine)
-			_, _ = s.WriteRune('\n')
-		}
 		optional := ""
 		if jsonOptional || tsType.Optional {
 			optional = "?"
 		}
-		_, _ = s.WriteString(fmt.Sprintf("%sreadonly %s%s: %s\n", indent, jsonName, optional, tsType.ValueType))
+		valueType := tsType.ValueType
+		if tsType.GenericValue != "" {
+			valueType = tsType.GenericValue
+			// This map we are building is just gathering all the generics used
+			// by our fields. We will use this map for our export type line.
+			// This isn't actually required since we can get it from the obj
+			// itself, but this ensures we actually use all the generic fields
+			// we place in the export line. If we are missing one from this map,
+			// that is a developer error. And we might as well catch it.
+			for name, constraint := range tsType.GenericTypes {
+				if _, ok := genericsUsed[name]; ok {
+					// Don't add a generic twice
+					// TODO: We should probably check that the generic mapping is
+					// 	not a different type. Like 'T' being referenced to 2 different
+					//	constraints. I don't think this is possible though in valid
+					// 	go, so I'm going to ignore this for now.
+					continue
 				}
-	_, _ = s.WriteString("}\n")
-	return s.String(), nil
+				genericsUsed[name] = constraint
+			}
+		}
+
+		if tsType.AboveTypeLine != "" {
+			// Just append these as fields. We should fix this later.
+			state.Fields = append(state.Fields, tsType.AboveTypeLine)
+		}
+		state.Fields = append(state.Fields, fmt.Sprintf("%sreadonly %s%s: %s", indent, jsonName, optional, valueType))
+	}
+
+	// This is implemented to ensure the correct order of generics on the
+	// top level structure. Ordering of generic fields is important, and
+	// we want to match the same order as Golang. The gathering of generic types
+	// from our fields does not guarantee the order.
+	named, ok := obj.(*types.TypeName)
+	if !ok {
+		return "", xerrors.Errorf("generic param ordering undefined on %q", obj.Name())
+	}
+
+	namedType, ok := named.Type().(*types.Named)
+	if !ok {
+		return "", xerrors.Errorf("generic param %q unexpected type %q", obj.Name(), named.Type().String())
+	}
+
+	// Ensure proper generic param ordering
+	params := namedType.TypeParams()
+	for i := 0; i < params.Len(); i++ {
+		param := params.At(i)
+		name := param.String()
+
+		constraint, ok := genericsUsed[param.String()]
+		if !ok {
+			// If this error is thrown, it is because you have defined a
+			// generic field on a structure, but did not use it in your
+			// fields. If this happens, remove the unused generic on
+			// the top level structure. We **technically** can implement
+			// this still, but it's not a case we need to support.
+			// Example:
+			//	type Foo[A any] struct {
+			//	  Bar string
+			//	}
+			return "", xerrors.Errorf("generic param %q missing on %q, fix your data structure", name, obj.Name())
+		}
+
+		state.Generics = append(state.Generics, fmt.Sprintf("%s extends %s", name, constraint))
+	}
+
+	data := bytes.NewBuffer(make([]byte, 0))
+	err = tpl.Execute(data, state)
+	if err != nil {
+		return "", xerrors.Errorf("execute struct template: %w", err)
+	}
+	return data.String(), nil
 }
 
 type TypescriptType struct {
+	// GenericTypes is a map of generic name to actual constraint.
+	// We return these, so we can bubble them up if we are recursively traversing
+	// a nested structure. We duplicate these at the top level.
+	// Example: 'C = comparable'.
+	GenericTypes map[string]string
+	// GenericValue is the value using the Generic name, rather than the constraint.
+	// This is only usedful if you can use the generic syntax. Things like maps
+	// don't currently support this, and will use the ValueType instead.
+	// Example:
+	//	Given the Golang
+	//	  type Foo[C comparable] struct {
+	//		  Bar C
+	//	  }
+	// 	The field `Bar` will return:
+	//	  TypescriptType {
+	//	    ValueType: "comparable",
+	//	    GenericValue: "C",
+	//	    GenericTypes: map[string]string{
+	//		  "C":"comparable"
+	//	    }
+	//    }
+	GenericValue string
+	// ValueType is the typescript value type. This is the actual type or
+	// generic constraint. This can **always** be used without special handling.
 	ValueType string
 	// AboveTypeLine lets you put whatever text you want above the typescript
 	// type line.
@@ -456,10 +690,40 @@ func (g *Generator) typescriptType(ty types.Type) (TypescriptType, error) {
 		// put the name as it will be defined in the typescript codeblock
 		// we generate.
 		name := n.Obj().Name()
+		genericName := ""
+		genericTypes := make(map[string]string)
 		if obj := g.pkg.Types.Scope().Lookup(name); obj != nil {
 			// Sweet! Using other typescript types as fields. This could be an
 			// enum or another struct
-			return TypescriptType{ValueType: name}, nil
+			if args := n.TypeArgs(); args != nil && args.Len() > 0 {
+				genericConstraints := make([]string, 0, args.Len())
+				genericNames := make([]string, 0, args.Len())
+				for i := 0; i < args.Len(); i++ {
+					genType, err := g.typescriptType(args.At(i))
+					if err != nil {
+						return TypescriptType{}, xerrors.Errorf("generic field %q<%q>: %w", name, args.At(i).String(), err)
+					}
+
+					if param, ok := args.At(i).(*types.TypeParam); ok {
+						// Using a generic defined by the parent.
+						gname := param.Obj().Name()
+						genericNames = append(genericNames, gname)
+						genericTypes[gname] = genType.ValueType
+					} else {
+						// Defining a generic
+						genericNames = append(genericNames, genType.ValueType)
+					}
+
+					genericConstraints = append(genericConstraints, genType.ValueType)
+				}
+				genericName = name + fmt.Sprintf("<%s>", strings.Join(genericNames, ", "))
+				name += fmt.Sprintf("<%s>", strings.Join(genericConstraints, ", "))
+			}
+			return TypescriptType{
+				GenericTypes: genericTypes,
+				GenericValue: genericName,
+				ValueType:    name,
+			}, nil
 		}
 
 		// If it's a struct, just use the name of the struct type
@@ -494,6 +758,50 @@ func (g *Generator) typescriptType(ty types.Type) (TypescriptType, error) {
 				AboveTypeLine: indentedComment("eslint-disable-next-line")}, nil
 		}
 		return TypescriptType{}, xerrors.New("only empty interface types are supported")
+	case *types.TypeParam:
+		_, ok := ty.Underlying().(*types.Interface)
+		if !ok {
+			// If it's not an interface, it is likely a usage of generics that
+			// we have not hit yet. Feel free to add support for it.
+			return TypescriptType{}, xerrors.New("type param must be an interface")
+		}
+
+		generic := ty.Constraint()
+		// We don't mess with multiple packages, so just trim the package path
+		// from the name.
+		pkgPath := ty.Obj().Pkg().Path()
+		name := strings.TrimPrefix(generic.String(), pkgPath+".")
+
+		referenced := g.pkg.Types.Scope().Lookup(name)
+
+		if referenced == nil {
+			include, builtinString := g.isBuiltIn(name)
+			if !include {
+				// If we don't have the type constraint defined somewhere in the package,
+				// then we have to resort to using any.
+				return TypescriptType{
+					GenericTypes: map[string]string{
+						ty.Obj().Name(): "any",
+					},
+					GenericValue:  ty.Obj().Name(),
+					ValueType:     "any",
+					AboveTypeLine: fmt.Sprintf("// %q is an external type, so we use any", name),
+					Optional:      false,
+				}, nil
+			}
+			// Include the builtin for this type to reference
+			g.builtins[name] = builtinString
+		}
+
+		return TypescriptType{
+			GenericTypes: map[string]string{
+				ty.Obj().Name(): name,
+			},
+			GenericValue:  ty.Obj().Name(),
+			ValueType:     name,
+			AboveTypeLine: "",
+			Optional:      false,
+		}, nil
 	}
 
 	// These are all the other types we need to support.
@@ -501,6 +809,26 @@ func (g *Generator) typescriptType(ty types.Type) (TypescriptType, error) {
 	return TypescriptType{}, xerrors.Errorf("unknown type: %s", ty.String())
 }
 
+// isBuiltIn returns the string for a builtin type that we want to support
+// if the name is a reserved builtin type. This is for types like 'comparable'.
+// These types are not implemented in golang, so we just have to hardcode it.
+func (Generator) isBuiltIn(name string) (bool, string) {
+	// Note: @emyrk If we use constraints like Ordered, we can pull those
+	// dynamically from their respective packages. This is a method on Generator
+	// so if someone wants to implement that, they can find the respective package
+	// and type.
+	switch name {
+	case "comparable":
+		// To be complete, we include "any". Kinda sucks :(
+		return true, "export type comparable = boolean | number | string | any"
+	case "any":
+		// This is supported in typescript, we don't need to write anything
+		return true, ""
+	default:
+		return false, ""
+	}
+}
+
 func indentedComment(comment string) string {
 	return fmt.Sprintf("%s// %s", indent, comment)
 }

scripts/apitypings/main_test.go

@@ -0,0 +1,43 @@
+//go:build !windows
+// +build !windows
+
+// Windows tests fail because the \n\r vs \n. It's not worth trying
+// to replace newlines for os tests. If people start using this tool on windows
+// and are seeing problems, then we can add build tags and figure it out.
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestGeneration(t *testing.T) {
+	t.Parallel()
+	files, err := os.ReadDir("testdata")
+	require.NoError(t, err, "read dir")
+
+	for _, f := range files {
+		if !f.IsDir() {
+			// Only test directories
+			continue
+		}
+		f := f
+		t.Run(f.Name(), func(t *testing.T) {
+			t.Parallel()
+			dir := filepath.Join(".", "testdata", f.Name())
+			output, err := Generate("./" + dir)
+			require.NoErrorf(t, err, "generate %q", dir)
+
+			golden := filepath.Join(dir, f.Name()+".ts")
+			expected, err := os.ReadFile(golden)
+			require.NoErrorf(t, err, "read file %s", golden)
+			expectedString := strings.TrimSpace(string(expected))
+			output = strings.TrimSpace(output)
+			require.Equal(t, expectedString, output, "matched output")
+		})
+	}
+}

scripts/apitypings/testdata/README.md

@@ -0,0 +1,5 @@
+# How to add a unit test
+
+1. Create a new directory in `testdata`
+2. Name a go file `<directory_name>.go`. This file will generate the typescript.
+3. Name the expected typescript file `<directory_name>.ts`. This is the unit test's expected output.

scripts/apitypings/testdata/enums/enums.go

@@ -0,0 +1,10 @@
+package enums
+
+type Enum string
+
+const (
+	EnumFoo Enum = "foo"
+	EnumBar Enum = "bar"
+	EnumBaz Enum = "baz"
+	EnumQux Enum = "qux"
+)

scripts/apitypings/testdata/enums/enums.ts

@@ -0,0 +1,4 @@
+// Code generated by 'make coder/scripts/apitypings/main.go'. DO NOT EDIT.
+
+// From codersdk/enums.go
+export type Enum = "bar" | "baz" | "foo" | "qux"

scripts/apitypings/testdata/generics/generics.go

@@ -0,0 +1,43 @@
+package generics
+
+import "time"
+
+type Single interface {
+	string
+}
+
+type Custom interface {
+	string | bool | int | time.Duration | []string | *int
+}
+
+// StaticGeneric has all generic fields defined in the field
+type StaticGeneric struct {
+	Static GenericFields[string, int, time.Duration, string] `json:"static"`
+}
+
+// DynamicGeneric can has some dynamic fields
+type DynamicGeneric[A any, S Single] struct {
+	Dynamic    GenericFields[bool, A, string, S] `json:"dynamic"`
+	Comparable bool                              `json:"comparable"`
+}
+
+type ComplexGeneric[C comparable, S Single, T Custom] struct {
+	Dynamic    GenericFields[C, bool, string, S]       `json:"dynamic"`
+	Order      GenericFieldsDiffOrder[C, string, S, T] `json:"order"`
+	Comparable C                                       `json:"comparable"`
+	Single     S                                       `json:"single"`
+	Static     StaticGeneric                           `json:"static"`
+}
+
+type GenericFields[C comparable, A any, T Custom, S Single] struct {
+	Comparable C `json:"comparable"`
+	Any        A `json:"any"`
+
+	Custom           T `json:"custom"`
+	Again            T `json:"again"`
+	SingleConstraint S `json:"single_constraint"`
+}
+
+type GenericFieldsDiffOrder[A any, C comparable, S Single, T Custom] struct {
+	GenericFields[C, A, T, S]
+}

scripts/apitypings/testdata/generics/generics.ts

@@ -0,0 +1,43 @@
+// Code generated by 'make coder/scripts/apitypings/main.go'. DO NOT EDIT.
+
+// From codersdk/generics.go
+export interface ComplexGeneric<C extends comparable, S extends Single, T extends Custom> {
+  readonly dynamic: GenericFields<C, boolean, string, S>
+  readonly order: GenericFieldsDiffOrder<C, string, S, T>
+  readonly comparable: C
+  readonly single: S
+  readonly static: StaticGeneric
+}
+
+// From codersdk/generics.go
+export interface DynamicGeneric<A extends any, S extends Single> {
+  readonly dynamic: GenericFields<boolean, A, string, S>
+  readonly comparable: boolean
+}
+
+// From codersdk/generics.go
+export interface GenericFields<C extends comparable, A extends any, T extends Custom, S extends Single> {
+  readonly comparable: C
+  readonly any: A
+  readonly custom: T
+  readonly again: T
+  readonly single_constraint: S
+}
+
+// From codersdk/generics.go
+export interface GenericFieldsDiffOrder<A extends any, C extends comparable, S extends Single, T extends Custom> {
+  readonly GenericFields: GenericFields<C, A, T, S>
+}
+
+// From codersdk/generics.go
+export interface StaticGeneric {
+  readonly static: GenericFields<string, number, number, string>
+}
+
+// From codersdk/generics.go
+export type Custom = string | boolean | number | string[] | null
+
+// From codersdk/generics.go
+export type Single = string
+
+export type comparable = boolean | number | string | any