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<main>
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<h1 id="adding-rainbow-bracket-queries"><a class="header" href="#adding-rainbow-bracket-queries">Adding Rainbow Bracket Queries</a></h1>
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<p>Helix uses <code>rainbows.scm</code> tree-sitter query files to provide rainbow bracket
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functionality.</p>
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<p>Tree-sitter queries are documented in the tree-sitter online documentation.
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If you're writing queries for the first time, be sure to check out the section
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on <a href="https://tree-sitter.github.io/tree-sitter/syntax-highlighting#highlights">syntax highlighting queries</a> and on <a href="https://tree-sitter.github.io/tree-sitter/using-parsers#pattern-matching-with-queries">query syntax</a>.</p>
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<p>Rainbow queries have two captures: <code>@rainbow.scope</code> and <code>@rainbow.bracket</code>.
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<code>@rainbow.scope</code> should capture any node that increases the nesting level
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while <code>@rainbow.bracket</code> should capture any bracket nodes. Put another way:
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<code>@rainbow.scope</code> switches to the next rainbow color for all nodes in the tree
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under it while <code>@rainbow.bracket</code> paints captured nodes with the current
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rainbow color.</p>
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<p>For an example, let's add rainbow queries for the tree-sitter query (TSQ)
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language itself. These queries will go into a
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<code>runtime/queries/tsq/rainbows.scm</code> file in the repository root.</p>
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<p>First we'll add the <code>@rainbow.bracket</code> captures. TSQ only has parentheses and
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square brackets:</p>
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<pre><code class="language-tsq">["(" ")" "[" "]"] @rainbow.bracket
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</code></pre>
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<p>The ordering of the nodes within the alternation (square brackets) is not
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taken into consideration.</p>
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<blockquote>
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<p>Note: Why are these nodes quoted? Most syntax highlights capture text
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surrounded by parentheses. These are <em>named nodes</em> and correspond to the
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names of rules in the grammar. Brackets are usually written in tree-sitter
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grammars as literal strings, for example:</p>
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<pre><code class="language-js">{
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// ...
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arguments: $ => seq("(", repeat($.argument), ")"),
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// ...
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}
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</code></pre>
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<p>Nodes written as literal strings in tree-sitter grammars may be captured
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in queries with those same literal strings.</p>
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</blockquote>
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<p>Then we'll add <code>@rainbow.scope</code> captures. The easiest way to do this is to
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view the <code>grammar.js</code> file in the tree-sitter grammar's repository. For TSQ,
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that file is <a href="https://github.com/the-mikedavis/tree-sitter-tsq/blob/48b5e9f82ae0a4727201626f33a17f69f8e0ff86/grammar.js">here</a>. As we scroll down the <code>grammar.js</code>, we
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see that the <code>(alternation)</code>, (L36) <code>(group)</code> (L57), <code>(named_node)</code> (L59),
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<code>(predicate)</code> (L87) and <code>(wildcard_node)</code> (L97) nodes all contain literal
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parentheses or square brackets in their definitions. These nodes are all
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direct parents of brackets and happen to also be the nodes we want to change
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to the next rainbow color, so we capture them as <code>@rainbow.scope</code>.</p>
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<pre><code class="language-tsq">[
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(group)
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(named_node)
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(wildcard_node)
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(predicate)
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(alternation)
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] @rainbow.scope
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</code></pre>
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<p>This strategy works as a rule of thumb for most programming and configuration
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languages. Markup languages can be trickier and may take additional
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experimentation to find the correct nodes to use for scopes and brackets.</p>
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<p>The <code>:tree-sitter-subtree</code> command shows the syntax tree under the primary
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selection in S-expression format and can be a useful tool for determining how
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to write a query.</p>
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<h3 id="properties"><a class="header" href="#properties">Properties</a></h3>
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<p>The <code>rainbow.include-children</code> property may be applied to <code>@rainbow.scope</code>
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captures. By default, all <code>@rainbow.bracket</code> captures must be direct descendant
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of a node captured with <code>@rainbow.scope</code> in a syntax tree in order to be
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highlighted. The <code>rainbow.include-children</code> property disables that check and
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allows <code>@rainbow.bracket</code> captures to be highlighted if they are direct or
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indirect descendants of some node captured with <code>@rainbow.scope</code>.</p>
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<p>For example, this property is used in the HTML rainbow queries.</p>
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<p>For a document like <code><a>link</a></code>, the syntax tree is:</p>
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<pre><code class="language-tsq">(element ; <a>link</a>
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(start_tag ; <a>
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(tag_name)) ; a
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(text) ; link
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(end_tag ; </a>
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(tag_name))) ; a
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</code></pre>
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<p>If we want to highlight the <code><</code>, <code>></code> and <code></</code> nodes with rainbow colors, we
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capture them as <code>@rainbow.bracket</code>:</p>
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<pre><code class="language-tsq">["<" ">" "</"] @rainbow.bracket
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</code></pre>
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<p>And we capture <code>(element)</code> as <code>@rainbow.scope</code> because <code>(element)</code> nodes nest
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within each other: they increment the nesting level and switch to the next
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color in the rainbow.</p>
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<pre><code class="language-tsq">(element) @rainbow.scope
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</code></pre>
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<p>But this combination of <code>@rainbow.scope</code> and <code>@rainbow.bracket</code> will not
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highlight any nodes. <code><</code>, <code>></code> and <code></</code> are children of the <code>(start_tag)</code> and
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<code>(end_tag)</code> nodes. We can't capture <code>(start_tag)</code> and <code>(end_tag)</code> as
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<code>@rainbow.scope</code> because they don't nest other elements. We can fix this case
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by removing the requirement that <code><</code>, <code>></code> and <code></</code> are direct descendants of
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<code>(element)</code> using the <code>rainbow.include-children</code> property.</p>
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<pre><code class="language-tsq">((element) @rainbow.scope
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(#set! rainbow.include-children))
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</code></pre>
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<p>With this property set, <code><</code>, <code>></code>, and <code></</code> will highlight with rainbow colors
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even though they aren't direct descendents of the <code>(element)</code> node.</p>
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<p><code>rainbow.include-children</code> is not necessary for the vast majority of programming
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languages. It is only necessary when the node that increments the nesting level
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(changes rainbow color) is not the direct parent of the bracket node.</p>
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