Fix UnusedAssign false positive inside inline {% liquid ... style ... endstyle %}

.changeset/fix-unused-assign-inline-liquid-style.md

@@ -0,0 +1,5 @@
+---
+'@shopify/liquid-html-parser': patch
+---
+
+Fix false-positive UnusedAssign warnings for variables used inside a `style` block within an inline `{% liquid %}` tag. The inline-liquid raw-tag CST mapping parsed every raw-tag body as plain text, so variable references inside `{% liquid ... style ... echo foo ... endstyle %}` never became AST nodes and checks that walk the tree saw no usage. The mapping now mirrors the top-level `liquidRawTagImpl` behavior: `schema` and `raw` remain text, all other raw tags are parsed as Liquid so references inside `style` and friends are preserved. Fixes Shopify/theme-tools#465.

packages/liquid-html-parser/src/stage-1-cst.ts

@@ -1212,14 +1212,38 @@ function toCST<T>(
       name: 0,
       body: 4,
       children(nodes) {
-        return toCST(
-          source,
-          grammars,
-          TextNodeGrammar,
-          ['HelperMappings'],
-          nodes[4].sourceString,
-          offset + nodes[4].source.startIdx,
-        );
+        const nameNode = nodes[0];
+        const rawMarkupStringNode = nodes[4];
+        switch (nameNode.sourceString) {
+          // {% schema %} parses its content as a string and should not be visited
+          case 'schema':
+          // {% raw %} accepts syntax errors, we shouldn't try to parse that
+          case 'raw': {
+            return toCST(
+              source,
+              grammars,
+              TextNodeGrammar,
+              ['HelperMappings'],
+              rawMarkupStringNode.sourceString,
+              offset + rawMarkupStringNode.source.startIdx,
+            );
+          }
+
+          // Match the top-level liquidRawTagImpl behavior so variables
+          // referenced inside {% liquid ... style ... endstyle %} are
+          // detected as used by checks that walk the AST. The body is
+          // still inline-liquid, so re-parse with LiquidStatement.
+          default: {
+            return toCST(
+              source,
+              grammars,
+              grammars.LiquidStatement,
+              ['HelperMappings', 'LiquidMappings', 'LiquidStatement'],
+              rawMarkupStringNode.sourceString,
+              offset + rawMarkupStringNode.source.startIdx,
+            );
+          }
+        }
       },
       whitespaceStart: null,
       whitespaceEnd: null,

packages/theme-check-common/src/checks/unused-assign/index.spec.ts

@@ -114,6 +114,25 @@ describe('Module: UnusedAssign', () => {
     }
   });
 
+  it('should not report unused assigns for variables used inside a style block within {% liquid %}', async () => {
+    const sourceCode = `
+      {%- liquid
+        assign shopName = shop.name
+        capture example
+          echo 'Shopify'
+        endcapture
+
+        style
+          echo example
+          echo shopName
+        endstyle
+      -%}
+    `;
+
+    const offenses = await runLiquidCheck(UnusedAssign, sourceCode);
+    expect(offenses).to.be.empty;
+  });
+
   it('should not report unused assigns for things used in a HTML raw-like tag', async () => {
     const tags = ['style', 'script'];
     for (const tag of tags) {