Check

Check is a Go library for statically type-checking text/template and html/template. It helps catch template/type mismatches early, making refactoring safer when changing types or templates.

To use it, call Execute and provide:

• a types.Type for the template’s data (.), and
• the template’s parse.Tree.

See example_test.go for a working example.

Originally built as part of muxt, this package also powers the muxt check CLI command. If you only need command-line checks, use muxt check directly. Unlike muxt, which requires templates to be defined as global variables, this package lets you map templates to data parameters more flexibly (at the cost of some verbosity).

For a more robust and easier-to-configure alternative, consider jba/templatecheck.

Key Types and Functions

• Global Holds type and template resolution state. Constructed with NewGlobal.

• Execute Entry point to validate a template tree against a given types.Type.

• TreeFinder / FindTreeFunc Resolves other templates by name (wrapping Template.Lookup).

• Functions A set of callable template functions. Implements CallChecker.

  • Use DefaultFunctions(pkg *types.Package) to get the standard built-ins.
  • Extend with Functions.Add.

• CallChecker Interface for validating function calls within templates.

Limitations

1. Type required You must provide a types.Type that represents the template’s root context (.).

2. Function sets Currently, default functions do not differentiate between text/template and html/template.

3. Third-party template packages Compatibility with specialized template libraries (e.g. safehtml) has not been fully tested.

4. Runtime-only errors Execute checks static type consistency but cannot detect runtime conditions such as out-of-range indexes. The standard library will try to dereference boxed types that may contain any type. Errors introduced by changes on a boxed type can not be caught by this package.