feat: add ParseFile and Valid

Assisted-by: GLM 5.3 Flash

interpres.go

@@ -24,6 +24,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"os"
 	"slices"
 )
 
@@ -127,6 +128,31 @@ func ParseMapContext(ctx context.Context, data []byte) (map[string]any, error) {
 	return tree, err
 }
 
+// ParseFile reads the TOML document at path and parses it into a Document,
+// the shape Parse gives. Every error names the file it came from: a read
+// failure and a parse failure alike carry the path as their first words,
+// wrapped so errors.AsType still reaches the SyntaxError inside.
+func ParseFile(path string) (*Document, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("%s: %w", path, err)
+	}
+	doc, err := Parse(data)
+	if err != nil {
+		return nil, fmt.Errorf("%s: %w", path, err)
+	}
+	return doc, nil
+}
+
+// Valid reports whether data is a valid TOML document: nil when the parser
+// accepts it, and the parse error when it does not. It is the library call
+// the -validate mode of interpres-decode is built on, and it reads nothing
+// but the bytes it is given.
+func Valid(data []byte) error {
+	_, err := ParseMapContext(context.Background(), data)
+	return err
+}
+
 // parseOptions bound the work one parse may do and the shape it produces. A
 // zero field takes the default.
 type parseOptions struct {