feat(kiosk): resolve constant plugin IDs, overrides and the CheckT helper

- kiosk.ReadIdentity: ID()/Requires() as literals or constants across packages and modules, read with go/parser, never run
- plugin minimums from go.mod requires; v0.0.0 is an error, a pseudo-version warns
- kiosk.Validate, kiosk.CheckT (no testing import)
- plugin:add reads IDs through kiosk.ReadIdentity, so const-ID plugins register

modules/kiosk/derive.go

@@ -7,13 +7,10 @@ import (
 	"errors"
 	"fmt"
 	"go/ast"
-	"go/parser"
-	"go/token"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"regexp"
-	"strconv"
 	"strings"
 
 	"github.com/yuin/goldmark"
@@ -97,17 +94,19 @@ func Derive(ctx context.Context, dir string, opts DeriveOptions) (Manifest, []st
 	}
 	m.Framework = fw
 
-	ident, err := readLiteralIdentity(abs)
+	r := newResolver(ctx, abs)
+	r.modLoaded, r.root, r.mod = true, root, mod
+	ident, err := r.identity(abs)
 	if err != nil {
 		return Manifest{}, nil, err
 	}
 	m.ID = ident.ID
-	if len(ident.Requires) > 0 {
-		m.Requires = Requires{}
-		for _, id := range ident.Requires {
-			m.Requires[id] = ""
-		}
+	reqs, w, err := r.minimums(ident.Requires)
+	warnings = append(warnings, w...)
+	if err != nil {
+		return Manifest{}, warnings, err
 	}
+	m.Requires = reqs
 
 	existing, err := readExisting(abs)
 	if err != nil {
@@ -289,73 +288,6 @@ func plainText(n gast.Node, src []byte) string {
 	return strings.Join(strings.Fields(b.String()), " ")
 }
 
-// identity is what Task 2's reader returns: the literals of ID() and
-// Requires().
-type identity struct {
-	ID       string
-	Requires []string
-}
-
-// readLiteralIdentity reads the string literals returned by ID() and
-// Requires() in dir/plugin.go.
-func readLiteralIdentity(dir string) (identity, error) {
-	path := filepath.Join(dir, "plugin.go")
-	fset := token.NewFileSet()
-	file, err := parser.ParseFile(fset, path, nil, 0)
-	if err != nil {
-		return identity{}, fmt.Errorf("kiosk: parse %s: %w", path, err)
-	}
-	var id identity
-	var idErr, reqErr error
-	foundID := false
-	for _, decl := range file.Decls {
-		fn, ok := decl.(*ast.FuncDecl)
-		if !ok || fn.Recv == nil || fn.Body == nil {
-			continue
-		}
-		ret := lastReturn(fn)
-		switch fn.Name.Name {
-		case "ID":
-			foundID = true
-			lit, ok := ret.(*ast.BasicLit)
-			if !ok || lit.Kind != token.STRING {
-				idErr = fmt.Errorf("kiosk: %s: ID() must return a string literal", path)
-				continue
-			}
-			id.ID, _ = strconv.Unquote(lit.Value)
-		case "Requires":
-			switch e := ret.(type) {
-			case *ast.Ident:
-				if e.Name != "nil" {
-					reqErr = fmt.Errorf("kiosk: %s: Requires() must return nil or a []string literal", path)
-				}
-			case *ast.CompositeLit:
-				for _, el := range e.Elts {
-					lit, ok := el.(*ast.BasicLit)
-					if !ok || lit.Kind != token.STRING {
-						reqErr = fmt.Errorf("kiosk: %s: Requires() must return string literals", path)
-						break
-					}
-					s, _ := strconv.Unquote(lit.Value)
-					id.Requires = append(id.Requires, s)
-				}
-			default:
-				reqErr = fmt.Errorf("kiosk: %s: Requires() must return nil or a []string literal", path)
-			}
-		}
-	}
-	if !foundID {
-		return identity{}, fmt.Errorf("kiosk: %s has no ID() method", path)
-	}
-	if idErr != nil {
-		return identity{}, idErr
-	}
-	if reqErr != nil {
-		return identity{}, reqErr
-	}
-	return id, nil
-}
-
 // lastReturn is the single result of fn's last top-level return, or nil.
 func lastReturn(fn *ast.FuncDecl) ast.Expr {
 	var res ast.Expr