esync

commit 07f5a2a9598a85405baf42053eb6b9a360d952a1
parent a7b4d498c9a35333022ff0565bf206530b76ffea
Author: Erik Loualiche <eloualic@umn.edu>
Date:   Sun,  8 Mar 2026 15:09:30 -0400

feat: add shouldInclude path-prefix filtering to watcher

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Diffstat:
M
internal/watcher/watcher.go
 | 
64
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-----
M
internal/watcher/watcher_test.go
 | 
55
+++++++++++++++++++++++++++++++++++++++++++++++++++++++

2 files changed, 114 insertions(+), 5 deletions(-)
diff --git a/internal/watcher/watcher.go b/internal/watcher/watcher.go
@@ -5,6 +5,7 @@ package watcher
 import (
 	"os"
 	"path/filepath"
+	"strings"
 	"sync"
 	"time"
 
@@ -89,7 +90,9 @@ type Watcher struct {
 	fsw       *fsnotify.Watcher
 	debouncer *Debouncer
 	path      string
+	rootPath  string
 	ignores   []string
+	includes  []string
 	done      chan struct{}
 }
 
@@ -97,21 +100,28 @@ type Watcher struct {
 // debounce interval in milliseconds (defaults to 500 if 0). ignores is a
 // list of filepath.Match patterns to skip. handler is called after each
 // debounced event batch.
-func New(path string, debounceMs int, ignores []string, handler EventHandler) (*Watcher, error) {
+func New(path string, debounceMs int, ignores []string, includes []string, handler EventHandler) (*Watcher, error) {
 	if debounceMs <= 0 {
 		debounceMs = 500
 	}
 
+	absPath, err := filepath.Abs(path)
+	if err != nil {
+		absPath = path
+	}
+
 	fsw, err := fsnotify.NewWatcher()
 	if err != nil {
 		return nil, err
 	}
 
 	w := &Watcher{
-		fsw:     fsw,
-		path:    path,
-		ignores: ignores,
-		done:    make(chan struct{}),
+		fsw:      fsw,
+		path:     path,
+		rootPath: absPath,
+		ignores:  ignores,
+		includes: includes,
+		done:     make(chan struct{}),
 	}
 
 	w.debouncer = NewDebouncer(time.Duration(debounceMs)*time.Millisecond, handler)
@@ -162,6 +172,10 @@ func (w *Watcher) eventLoop() {
 				continue
 			}
 
+			if !w.shouldInclude(event.Name) {
+				continue
+			}
+
 			// If a new directory was created, watch it recursively
 			if event.Op&fsnotify.Create != 0 {
 				if info, err := os.Stat(event.Name); err == nil && info.IsDir() {
@@ -199,6 +213,39 @@ func (w *Watcher) shouldIgnore(path string) bool {
 	return false
 }
 
+// shouldInclude checks whether path falls within one of the configured include
+// prefixes. If no includes are configured, every path is included. The method
+// also returns true for ancestor directories of an include prefix (needed for
+// traversal) and for the root path itself.
+func (w *Watcher) shouldInclude(path string) bool {
+	if len(w.includes) == 0 {
+		return true
+	}
+
+	abs, err := filepath.Abs(path)
+	if err != nil {
+		abs = path
+	}
+
+	rel, err := filepath.Rel(w.rootPath, abs)
+	if err != nil || rel == "." {
+		return true
+	}
+
+	for _, inc := range w.includes {
+		incClean := filepath.Clean(inc)
+		// Path is the include prefix itself or is inside it
+		if rel == incClean || strings.HasPrefix(rel, incClean+string(filepath.Separator)) {
+			return true
+		}
+		// Path is an ancestor directory needed to reach the include prefix
+		if strings.HasPrefix(incClean, rel+string(filepath.Separator)) {
+			return true
+		}
+	}
+	return false
+}
+
 // addRecursive walks the directory tree rooted at path and adds every
 // directory to the fsnotify watcher. Individual files are not added
 // because fsnotify watches directories for events on their contents.
@@ -215,6 +262,13 @@ func (w *Watcher) addRecursive(path string) error {
 			return nil
 		}
 
+		if !w.shouldInclude(p) {
+			if info.IsDir() {
+				return filepath.SkipDir
+			}
+			return nil
+		}
+
 		if info.IsDir() {
 			return w.fsw.Add(p)
 		}
diff --git a/internal/watcher/watcher_test.go b/internal/watcher/watcher_test.go
@@ -110,3 +110,58 @@ func TestShouldIgnore(t *testing.T) {
 		}
 	}
 }
+
+// ---------------------------------------------------------------------------
+// 5. TestShouldInclude — verify include prefix matching
+// ---------------------------------------------------------------------------
+func TestShouldInclude(t *testing.T) {
+	w := &Watcher{
+		rootPath: "/project",
+		includes: []string{"src", "docs/api"},
+	}
+
+	tests := []struct {
+		path   string
+		expect bool
+	}{
+		{"/project/src/main.go", true},
+		{"/project/src/pkg/util.go", true},
+		{"/project/docs/api/readme.md", true},
+		{"/project/docs", true},           // ancestor of docs/api
+		{"/project/tmp/cache.bin", false},
+		{"/project/build/out.o", false},
+		{"/project", true},                // root always included
+	}
+
+	for _, tt := range tests {
+		got := w.shouldInclude(tt.path)
+		if got != tt.expect {
+			t.Errorf("shouldInclude(%q) = %v, want %v", tt.path, got, tt.expect)
+		}
+	}
+}
+
+// ---------------------------------------------------------------------------
+// 6. TestShouldIncludeEmptyMeansAll — empty includes means include everything
+// ---------------------------------------------------------------------------
+func TestShouldIncludeEmptyMeansAll(t *testing.T) {
+	w := &Watcher{
+		rootPath: "/project",
+		includes: nil,
+	}
+
+	tests := []struct {
+		path   string
+		expect bool
+	}{
+		{"/project/anything/at/all.go", true},
+		{"/project/tmp/cache.bin", true},
+	}
+
+	for _, tt := range tests {
+		got := w.shouldInclude(tt.path)
+		if got != tt.expect {
+			t.Errorf("shouldInclude(%q) = %v, want %v", tt.path, got, tt.expect)
+		}
+	}
+}