2 files changed, 47 insertions, 2 deletions
diff --git a/internal/config/load.go b/internal/config/load.go
index cd4d97c..3811802 100644
--- a/internal/config/load.go
+++ b/internal/config/load.go
@@ -20,6 +20,15 @@ type Config struct {
 	Dirs []*Dir
 }
 
+// readSource is the text of file: the caller's override when it has one,
+// else the file's own bytes.
+func readSource(overrides map[string][]byte, file string) ([]byte, error) {
+	if src, ok := overrides[file]; ok {
+		return src, nil
+	}
+	return os.ReadFile(file)
+}
+
 // DefaultFile is krino.conf in the XDG config directory.
 func DefaultFile() string {
 	return filepath.Join(xdg.ConfigHome(), "krino", "krino.conf")
@@ -34,7 +43,16 @@ func DirFile(mainFile, name string) string {
 // With names, only those directories are read, and each must be included.
 // The Config is nil only when the main file itself cannot be read.
 func Load(mainFile string, names ...string) (*Config, []*Diag) {
-	src, err := os.ReadFile(mainFile)
+	return LoadWith(mainFile, nil, names...)
+}
+
+// LoadWith is Load with some files' text supplied by the caller: overrides
+// maps a file path - mainFile, or DirFile(mainFile, name) - to the text to
+// read instead of that file's own, so an editor can have unsaved text
+// checked exactly as a run would read it (GUI design §1.3). A nil map is
+// Load.
+func LoadWith(mainFile string, overrides map[string][]byte, names ...string) (*Config, []*Diag) {
+	src, err := readSource(overrides, mainFile)
 	if errors.Is(err, fs.ErrNotExist) {
 		return nil, []*Diag{{File: mainFile, Msg: "not found; create it with: krino init"}}
 	}
@@ -62,7 +80,7 @@ func Load(mainFile string, names ...string) (*Config, []*Diag) {
 	}
 	for _, name := range want {
 		file := DirFile(mainFile, name)
-		src, err := os.ReadFile(file)
+		src, err := readSource(overrides, file)
 		if err != nil {
 			msg := err.Error()
 			if errors.Is(err, fs.ErrNotExist) {
diff --git a/internal/config/load_test.go b/internal/config/load_test.go
index 1cc3ac9..13ef9d8 100644
--- a/internal/config/load_test.go
+++ b/internal/config/load_test.go
@@ -115,3 +115,30 @@ func TestLockFile(t *testing.T) {
 		t.Errorf("LockFile = %q, want %q", got, want)
 	}
 }
+
+// TestLoadWithOverriddenText: LoadWith reads the text the caller supplies
+// instead of a file's own, so an editor can check what it has not saved yet
+// (GUI design §1.3); the files on disk are neither read differently nor
+// changed.
+func TestLoadWithOverriddenText(t *testing.T) {
+	h := t.TempDir()
+	t.Setenv("HOME", h)
+	main := filepath.Join(h, "krino.conf")
+	if err := os.MkdirAll(filepath.Join(h, "dirs"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	os.WriteFile(main, []byte("(include \"dl\")\n"), 0o644)
+	os.WriteFile(filepath.Join(h, "dirs", "dl.conf"), []byte("(path \"/tmp\")\n"), 0o644)
+
+	over := map[string][]byte{filepath.Join(h, "dirs", "dl.conf"): []byte("(path \"/tmp\")\n(rule \"r\" (move \"Out\"))\n")}
+	cfg, errs := LoadWith(main, over)
+	if len(errs) > 0 || len(cfg.Dirs) != 1 || len(cfg.Dirs[0].Rules) != 1 {
+		t.Fatalf("overridden text not used: %v %+v", errs, cfg.Dirs)
+	}
+	if _, errs := LoadWith(main, map[string][]byte{main: []byte("(include \"dl\"")}); len(errs) == 0 {
+		t.Error("a mistake in the overridden main file was not reported")
+	}
+	if cfg, errs := Load(main); len(errs) > 0 || len(cfg.Dirs[0].Rules) != 0 {
+		t.Errorf("the files on disk were read differently: %v %+v", errs, cfg.Dirs)
+	}
+}