internal/rosa: evaluate packages from fs

This migrates GNU sed to azalea, and resulting IR matches.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/state.go

@@ -52,7 +52,7 @@ func (handle *ArtifactH) UnmarshalJSON(data []byte) error {
 type HandleError ArtifactH
 
 func (e HandleError) Error() string {
-	return "artifact " + strconv.Quote(ArtifactH(e).String()) + " not available"
+	return "package " + strconv.Quote(ArtifactH(e).String()) + " not available"
 }
 
 type (
@@ -268,8 +268,38 @@ func (s *S) New(stage Stage) Toolchain {
 // Std is a convenience method that returns a [Toolchain] for the [Std] stage.
 func (s *S) Std() Toolchain { return s.New(Std) }
 
+// LoadError wraps panicked errors reaching [Toolchain.Load].
+type LoadError struct {
+	// Offending artifact handle.
+	Handle ArtifactH
+	// Recovered error.
+	Err error
+}
+
+func (e LoadError) Unwrap() error { return e.Err }
+func (e LoadError) Error() string {
+	return "cannot load " + strconv.Quote(e.Handle.String()) + ": " + e.Err.Error()
+}
+
 // Load returns the resulting [pkg.Artifact] of [ArtifactH].
 func (t Toolchain) Load(handle ArtifactH) (pkg.Artifact, string) {
+	defer func() {
+		r := recover()
+		if r == nil {
+			return
+		}
+
+		err, ok := r.(error)
+		if !ok {
+			panic(r)
+		}
+
+		if _, ok = err.(LoadError); ok {
+			panic(err)
+		}
+		panic(LoadError{handle, err})
+	}()
+
 	t.wantsArch()
 	e, ok := t.c[t.stage].Load(handle)
 	if ok {
@@ -552,6 +582,64 @@ func (s *S) Evaluate(r io.Reader, b fs.FS) error {
 	return nil
 }
 
+// EvaluateFS evaluates azalea files discovered in fsys. A file is evaluated if
+// it is at the top level and its name has the suffix ".az", or it is in a
+// top-level directory with the exact file name "package.az". The backing
+// filesystem is directly exposed to azalea pathnames.
+func (s *S) EvaluateFS(fsys fs.FS) error {
+	dents, err := fs.ReadDir(fsys, ".")
+	if err != nil {
+		return err
+	}
+
+	var r fs.File
+	for _, dent := range dents {
+		if dent.IsDir() {
+			var sub fs.FS
+			sub, err = fs.Sub(fsys, dent.Name())
+			if err != nil {
+				return err
+			}
+
+			r, err = sub.Open("package.az")
+			if errors.Is(err, fs.ErrNotExist) {
+				continue
+			}
+			if err != nil {
+				return err
+			}
+
+			err = s.Evaluate(r, sub)
+			if _err := r.Close(); err == nil {
+				err = _err
+			}
+			if err != nil {
+				return err
+			}
+			continue
+		}
+
+		if !dent.Type().IsRegular() ||
+			!strings.HasSuffix(dent.Name(), ".az") {
+			continue
+		}
+
+		r, err = fsys.Open(dent.Name())
+		if err != nil {
+			return err
+		}
+
+		err = s.Evaluate(r, fsys)
+		if _err := r.Close(); err == nil {
+			err = _err
+		}
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // SetGentooStage3 sets the Gentoo stage3 tarball url and checksum. It panics
 // if given zero values or if these values have already been set.
 func (s *S) SetGentooStage3(url string, checksum pkg.Checksum) {