Fix elseif / else indentation and support incomplete structures (#42)

Closes #36: `elseif` /
`else` statements are now correctly outdented, with the following line
now also indented as expected.

This PR leverages the `indent_pattern` configuration available to
language extensions, similar to other extensions (Ruby, Python, Julia,
Elixir) that work around tree-sitter indentation limitations.

Additionally, it provides fallback indentation for control structures
and function definitions when the syntax tree is temporarily incomplete
(e.g. an `if` statement without its closing `end`), which is especially
useful when not using code snippets. These cases cannot yet be handled
by tree-sitter alone. See the [Julia
extension](https://github.com/JuliaEditorSupport/zed-julia/blob/main/languages/julia/config.toml)
for related rationale.

Co-authored-by: Finn Evers <finn@zed.dev>

Author: Fringale

languages/lua/config.toml

@@ -12,3 +12,12 @@ brackets = [
     { start = "'", end = "'", close = true, newline = false, not_in = ["string"] },
 ]
 collapsed_placeholder = "--[ ... ]--"
+
+# Fallback indent rules to complement tree-sitter.
+# Handle incomplete structures (e.g. before typing `end`).
+increase_indent_pattern = "^\\s*(if|elseif|else|do|while|for|repeat|((local|global)\\s+)?function|.+=\\s*function|.*[,(]\\s*function)\\b"
+
+# Fallback outdent rules to complement tree-sitter.
+# Fix `elseif` / `else` handling, and outdent `end` / `until` even when the structure is incomplete.
+# Avoids relying on `valid_after` contexts, which depend on tree-sitter queries (`@start.*` captures).
+decrease_indent_pattern = "^\\s*(elseif|else|end|until)\\b"