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Section Context & Falsy Edge Cases

Status: Mostly supported, with two documented divergences from the spec.

Summary​

Bigodin's runtime semantics for {{#x}}...{{/x}} and {{^x}}...{{/x}} match the Mustache spec for the common cases:

  • null, undefined, false, 0, "", and empty arrays are falsy on both the positive and inverted branches.
  • Non-empty arrays iterate, pushing each item onto the context stack.
  • Object values push as the new context.
  • Truthy scalars (strings, numbers, true) render the body once.

The Falsey, Truthy, Null is falsey, Context, Empty List, List, Doubled, and similar tests in sections.json and inverted.json all pass.

Documented divergences​

The following spec tests are deliberately skipped (SKIPPED_FEATURES in test/spec.spec.ts):

  • Parent contexts
  • List Contexts
  • Deeply Nested Contexts
  • Variable test

All four require automatic context-stack walk on a missing key: when a name isn't found in the current frame, Mustache walks up the stack to find it. Bigodin uses Handlebars-style strict scoping; you must walk explicitly with $parent and $root:

{{#post}}{{$parent.author.name}}{{/post}}

A second divergence (not currently exercised by an active spec test, but worth flagging) is truthy-scalar context push:

{{#name}}Hello, {{.}}{{/name}}     name: "Alice"

In Mustache, the section pushes "Alice" onto the context stack so {{.}} resolves to it. In Bigodin, truthy scalars render the body but do not push: {{.}} resolves to whatever was on top of the stack before the section opened. This matches Handlebars' "use {{#if}} for truthiness, {{#each}} for iteration" idiom.

Why the divergence​

Both rules trade a small amount of spec conformance for clearer scoping rules:

  • Strict scoping (no auto-walk) makes it impossible for a deeply-nested template to accidentally pick up a name from an outer frame, which is a common source of bugs in Handlebars-style templates that grow over time.
  • Not pushing scalars keeps the context stack "shape-stable" - the top frame is always an object or an array element, never an opaque scalar - which simplifies reasoning about {{$parent}} and {{$root}}.

If your templates require Mustache's auto-walk behavior, prefer using explicit $parent.foo / $root.foo paths or restructure the data so the relevant key lives in the current frame.

Implementation note​

The relevant runtime is src/runner/block.ts runBlock. The negated branch and the empty-array guard share the same falsy check, so {{^list}}...{{/list}} over list: [] correctly renders the body. Path resolution lives in src/runner/path-expression.ts; it does not walk up the context stack on a miss - $parent, $root, and $this are the explicit walkers.