Module snippets 

Snippet parsing + placeholder navigation primitives.

This module implements a pragmatic subset of TextMate / VS Code snippet syntax that is sufficient for kernel features like:

• LSP completion items with insertTextFormat == 2 (snippets)
• placeholder ($1, ${1:default}) navigation (tab / shift-tab)
• best-effort handling of choices (${1|a,b,c|}) and variables (${TM_FILENAME:foo.rs})

Goals:

• Keep the kernel UI-agnostic: no rendering, no popup UI for choices.
• Prefer “do something reasonable” over rejecting malformed snippet text.
• Express all ranges in character offsets (Rust char indices), consistent with the rest of editor-core.

Structs

SnippetRange

A half-open character range (start..end) within a snippet’s expanded text.

SnippetSession

An active snippet session tracked in document coordinates.

SnippetTabstop

A numbered tabstop within a snippet.

SnippetTemplate

An expanded snippet template.

Functions

parse_snippet

Parse a TextMate/VS Code-style snippet string into an expanded template.