feat: add ParseFile and Valid

Assisted-by: GLM 5.3 Flash

interpres_test.go

@@ -6,6 +6,8 @@ package interpres
 import (
 	"errors"
 	"math"
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 	"time"
@@ -726,3 +728,48 @@ func TestParseNestingLimit(t *testing.T) {
 		t.Errorf("Msg = %q, want it to name the nesting limit", se.Msg)
 	}
 }
+
+func TestParseFile(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "config.toml")
+	if err := os.WriteFile(path, []byte("port = 8080\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	doc, err := ParseFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := doc.Map()["port"]; got != int64(8080) {
+		t.Errorf("port = %v, want 8080", got)
+	}
+
+	_, err = ParseFile(filepath.Join(t.TempDir(), "missing.toml"))
+	if err == nil || !strings.Contains(err.Error(), "missing.toml") {
+		t.Errorf("read error = %v, want it to name the file", err)
+	}
+
+	bad := filepath.Join(t.TempDir(), "broken.toml")
+	if err := os.WriteFile(bad, []byte("port =\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	_, err = ParseFile(bad)
+	if err == nil || !strings.Contains(err.Error(), "broken.toml") {
+		t.Errorf("parse error = %v, want it to name the file", err)
+	}
+	s, ok := errors.AsType[*SyntaxError](err)
+	if !ok || s.Line != 1 {
+		t.Errorf("parse error = %v, want a SyntaxError with line 1 inside", err)
+	}
+}
+
+func TestValid(t *testing.T) {
+	if err := Valid([]byte("a = 1\n[t]\nb = 2\n")); err != nil {
+		t.Errorf("Valid(valid) = %v, want nil", err)
+	}
+	err := Valid([]byte("a = \n"))
+	if err == nil {
+		t.Fatal("Valid(invalid) = nil, want an error")
+	}
+	if _, ok := errors.AsType[*SyntaxError](err); !ok {
+		t.Errorf("Valid(invalid) = %v, want a SyntaxError", err)
+	}
+}