Extract rule: template-style-concatenation

[NullVoxPopuli]

Split from #2371.

[NullVoxPopuli-ai-agent]

Review: template-style-concatenation

Compared against ember-template-lint style-concatenation.js.

General Correctness

1. Faithful port: The logic correctly mirrors the original. The original checks ElementNode for a style attribute whose value is either a ConcatStatement or a MustacheStatement with a concat helper path. The ESLint port does the same with the appropriate Glimmer-prefixed AST node types. Good.

2. Error message difference: The original uses 'Concatenated styles must be marked as \htmlSafe`.'but the ESLint port uses'Avoid string concatenation in style attributes. Use a computed property with htmlSafe instead.'. This is a meaningful difference in messaging. The original's message is more specific and actionable (telling users to use htmlSafe`). The port's message is more prescriptive (suggesting computed properties). Consider aligning with the original message for consistency, or at least noting the intentional change.

3. Attribute finding approach: The original uses AstNodeInfo.findAttribute(node, 'style') while the port uses node.attributes?.find((a) => a.name === 'style'). These are functionally equivalent. Good.

4. Tests: Good coverage for both gjs and hbs modes. The test cases cover ConcatStatement (interpolated strings like style="color: {{this.color}}") and MustacheStatement with concat helper. Valid cases correctly include html-safe wrapping around concat.

Scope Analysis (gjs/gts)

This rule checks path.original === 'concat' to detect the concat helper used in style attributes. In gjs/gts, concat could theoretically be shadowed by a local import. However, the concat helper is a very common Ember built-in, and the rule is specifically checking for it within a style attribute's mustache value -- a very specific context. The risk of false positives from shadowing is minimal. That said, for completeness, scope analysis could verify that concat refers to the built-in, but this is low priority.

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🤖 Automated review comparing with ember-template-lint source