Resolve candidate file destinations

internal/validation/tree.go

@@ -3,6 +3,8 @@ package validation
 import (
 	"context"
 	"fmt"
+	"path"
+	"strings"
 
 	"gitea.maximumdirect.net/eric/ReleaseKit/internal/git"
 )
@@ -13,6 +15,7 @@ type CandidateTree struct {
 	repositoryDir string
 	entries       []git.TreeEntry
 	byPath        map[string]int
+	directories   map[string]struct{}
 	blobs         map[string][]byte
 }
 
@@ -27,10 +30,15 @@ func ReadCandidateTree(ctx context.Context, repositoryDir, commit string) (*Cand
 		repositoryDir: repositoryDir,
 		entries:       entries,
 		byPath:        make(map[string]int, len(entries)),
+		directories:   make(map[string]struct{}),
 		blobs:         make(map[string][]byte),
 	}
+	tree.directories["."] = struct{}{}
 	for index, entry := range entries {
 		tree.byPath[entry.Path] = index
+		for directory := path.Dir(entry.Path); directory != "."; directory = path.Dir(directory) {
+			tree.directories[directory] = struct{}{}
+		}
 	}
 	return tree, nil
 }
@@ -70,3 +78,89 @@ func (tree *CandidateTree) Entry(path string) (git.TreeEntry, bool) {
 	}
 	return tree.entries[index], true
 }
+
+// DestinationKind classifies a committed local destination.
+type DestinationKind string
+
+const (
+	DestinationEntry           DestinationKind = "entry"
+	DestinationDirectory       DestinationKind = "directory"
+	DestinationMissing         DestinationKind = "missing"
+	DestinationOutsideCheckout DestinationKind = "outside-checkout"
+	DestinationSubmodule       DestinationKind = "submodule"
+	DestinationSymlinkCycle    DestinationKind = "symlink-cycle"
+)
+
+// Destination records the resolved identity and its classification.
+type Destination struct {
+	Kind DestinationKind
+	Path string
+}
+
+// ResolveDestination resolves a repository-relative destination from the
+// source file's directory using only the captured Git tree.
+func (tree *CandidateTree) ResolveDestination(ctx context.Context, sourcePath, destination string) (Destination, error) {
+	if strings.HasPrefix(destination, "/") {
+		return Destination{Kind: DestinationOutsideCheckout, Path: path.Clean(destination)}, nil
+	}
+	resolved := path.Clean(path.Join(path.Dir(sourcePath), destination))
+	if outsideCheckout(resolved) {
+		return Destination{Kind: DestinationOutsideCheckout, Path: resolved}, nil
+	}
+	seen := make(map[string]struct{})
+	for {
+		components := strings.Split(resolved, "/")
+		partial := ""
+		restarted := false
+		for index, component := range components {
+			partial = path.Join(partial, component)
+			remaining := strings.Join(components[index+1:], "/")
+			entry, exists := tree.Entry(partial)
+			if !exists {
+				if _, directory := tree.directories[partial]; !directory {
+					return Destination{Kind: DestinationMissing, Path: resolved}, nil
+				}
+				continue
+			}
+			if entry.Mode == "160000" {
+				return Destination{Kind: DestinationSubmodule, Path: path.Join(partial, remaining)}, nil
+			}
+			if entry.Mode == "120000" {
+				state := partial + "\x00" + remaining
+				if _, cycle := seen[state]; cycle {
+					return Destination{Kind: DestinationSymlinkCycle, Path: partial}, nil
+				}
+				seen[state] = struct{}{}
+				linkText, err := tree.ReadFile(ctx, partial)
+				if err != nil {
+					return Destination{}, fmt.Errorf("read committed symlink %q: %w", partial, err)
+				}
+				target := string(linkText)
+				if strings.HasPrefix(target, "/") {
+					return Destination{Kind: DestinationOutsideCheckout, Path: target}, nil
+				}
+				resolved = path.Clean(path.Join(path.Dir(partial), target, remaining))
+				if outsideCheckout(resolved) {
+					return Destination{Kind: DestinationOutsideCheckout, Path: resolved}, nil
+				}
+				restarted = true
+				break
+			}
+			if remaining != "" {
+				return Destination{Kind: DestinationMissing, Path: resolved}, nil
+			}
+			return Destination{Kind: DestinationEntry, Path: partial}, nil
+		}
+		if restarted {
+			continue
+		}
+		if _, directory := tree.directories[resolved]; directory {
+			return Destination{Kind: DestinationDirectory, Path: resolved}, nil
+		}
+		return Destination{Kind: DestinationMissing, Path: resolved}, nil
+	}
+}
+
+func outsideCheckout(name string) bool {
+	return name == ".." || strings.HasPrefix(name, "../")
+}