From 8013a204d123c8ea13dd134e275956d3ebb654ab Mon Sep 17 00:00:00 2001
From: Mike <mike@alvo.co.uk>
Date: Thu, 14 May 2026 19:50:42 +0100
Subject: [PATCH] fix: build internal/config on Windows

internal/config/config.go used syscall.Flock and syscall.LOCK_EX/LOCK_UN
directly, so `go install github.com/marcus/td@latest` failed on Windows
with `undefined: syscall.Flock`.

Split withConfigLock into platform-specific files, mirroring the existing
pattern in internal/db/lock_{unix,windows}.go and
internal/serve/portfile_{unix,windows}.go:

  - lock_unix.go    -> flock-based (unchanged behavior)
  - lock_windows.go -> LockFileEx with LOCKFILE_EXCLUSIVE_LOCK (blocking,
                       matching the Unix LOCK_EX semantics)

All locking-relevant config tests pass on Windows, including the
TestEdgeCases/concurrent_operations stress test that drives ten goroutines
through SetFocus/SetActiveWorkSession concurrently. The two
TestPermissionErrors failures are pre-existing (the test uses POSIX
chmod 0000/0555, which don't map to Windows ACLs) and unrelated to this
change.
---
 internal/config/config.go       | 26 +++----------------
 internal/config/lock_unix.go    | 31 ++++++++++++++++++++++
 internal/config/lock_windows.go | 46 +++++++++++++++++++++++++++++++++
 3 files changed, 80 insertions(+), 23 deletions(-)
 create mode 100644 internal/config/lock_unix.go
 create mode 100644 internal/config/lock_windows.go

diff --git a/internal/config/config.go b/internal/config/config.go
index b257239c..88940747 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -6,7 +6,6 @@ import (
 	"encoding/json"
 	"os"
 	"path/filepath"
-	"syscall"
 
 	"github.com/marcus/td/internal/models"
 )
@@ -14,6 +13,9 @@ import (
 const configFile = ".todos/config.json"
 const lockFile = ".todos/config.json.lock"
 
+// withConfigLock serializes access to config.json using an OS file lock.
+// Implemented per-platform in lock_unix.go (flock) and lock_windows.go (LockFileEx).
+
 // Title validation defaults
 const (
 	DefaultTitleMinLength = 15
@@ -75,28 +77,6 @@ func Save(baseDir string, cfg *models.Config) error {
 	return os.Rename(tmpName, configPath)
 }
 
-// withConfigLock serializes access to config.json using flock
-func withConfigLock(baseDir string, fn func() error) error {
-	lockPath := filepath.Join(baseDir, lockFile)
-
-	if err := os.MkdirAll(filepath.Dir(lockPath), 0755); err != nil {
-		return err
-	}
-
-	f, err := os.OpenFile(lockPath, os.O_CREATE|os.O_RDWR, 0644)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-
-	if err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX); err != nil {
-		return err
-	}
-	defer func() { _ = syscall.Flock(int(f.Fd()), syscall.LOCK_UN) }()
-
-	return fn()
-}
-
 // SetFocus sets the focused issue ID
 func SetFocus(baseDir string, issueID string) error {
 	return withConfigLock(baseDir, func() error {
diff --git a/internal/config/lock_unix.go b/internal/config/lock_unix.go
new file mode 100644
index 00000000..fd8d9261
--- /dev/null
+++ b/internal/config/lock_unix.go
@@ -0,0 +1,31 @@
+//go:build unix
+
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"syscall"
+)
+
+// withConfigLock serializes access to config.json using flock.
+func withConfigLock(baseDir string, fn func() error) error {
+	lockPath := filepath.Join(baseDir, lockFile)
+
+	if err := os.MkdirAll(filepath.Dir(lockPath), 0755); err != nil {
+		return err
+	}
+
+	f, err := os.OpenFile(lockPath, os.O_CREATE|os.O_RDWR, 0644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	if err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX); err != nil {
+		return err
+	}
+	defer func() { _ = syscall.Flock(int(f.Fd()), syscall.LOCK_UN) }()
+
+	return fn()
+}
diff --git a/internal/config/lock_windows.go b/internal/config/lock_windows.go
new file mode 100644
index 00000000..6c709882
--- /dev/null
+++ b/internal/config/lock_windows.go
@@ -0,0 +1,46 @@
+//go:build windows
+
+package config
+
+import (
+	"os"
+	"path/filepath"
+
+	"golang.org/x/sys/windows"
+)
+
+// withConfigLock serializes access to config.json using LockFileEx.
+func withConfigLock(baseDir string, fn func() error) error {
+	lockPath := filepath.Join(baseDir, lockFile)
+
+	if err := os.MkdirAll(filepath.Dir(lockPath), 0755); err != nil {
+		return err
+	}
+
+	f, err := os.OpenFile(lockPath, os.O_CREATE|os.O_RDWR, 0644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	// LockFileEx with LOCKFILE_EXCLUSIVE_LOCK (blocking) locks the first byte
+	// of the file, which is sufficient for whole-file mutual exclusion since
+	// every contender uses the same offset/length.
+	ol := new(windows.Overlapped)
+	if err := windows.LockFileEx(
+		windows.Handle(f.Fd()),
+		windows.LOCKFILE_EXCLUSIVE_LOCK,
+		0, // reserved
+		1, // lock 1 byte
+		0, // high bits of length
+		ol,
+	); err != nil {
+		return err
+	}
+	defer func() {
+		ul := new(windows.Overlapped)
+		_ = windows.UnlockFileEx(windows.Handle(f.Fd()), 0, 1, 0, ul)
+	}()
+
+	return fn()
+}