`typescript-eslint` error on a file

[boris-petrov]

import Component from '@glimmer/component';

export default class MyComponent extends Component {
  <template>
    {{!  `asd` `qwe` `zxc` `undefined` `asd` }}
    {{! `@foo` }}
    123
  </template>
}

@NullVoxPopuli thanks for fixing #226! Above is (almost) the same example which now compiles but it gives a @typescript-eslint/no-unused-expressions error which doesn't make sense. Maybe related to #229.

[NullVoxPopuli-ai-agent]

Reproduced, and root-caused — the bug is in ember-estree's placeholder generation, not in this parser directly. Fix: NullVoxPopuli/ember-estree#69.

What happens

ember-estree replaces each <template>...</template> region with a same-length JS placeholder (static{`...`} for class members) before handing the file to the JS/TS parser, then splices the real Glimmer AST back in by matching ranges. When building the placeholder it backslash-escapes ` and $ in the template content, which grows the placeholder by 1 char per occurrence — but the available padding slack is fixed at 11 chars for class-member templates (<template></template> = 21 chars minus the 10-char static{`...`} wrapper; expression templates get 19).

Once the escapes exceed that slack, the placeholder is longer than the original region, the range match fails, and the raw StaticBlock { ... } placeholder leaks into the AST — which is what @typescript-eslint/no-unused-expressions then flags. All offsets after the template shift too, so it's the same family as #229's symptoms.

Your snippet has exactly 12 backticks across the two comments — one over the limit. With 11 it lints clean. $ characters trigger it the same way (12+ $s in template content, no backticks needed).

The fix

NullVoxPopuli/ember-estree#69 blanks out `/$ instead of escaping them (the placeholder content is discarded when the Glimmer AST is spliced in, so only its length matters). Verified against your exact snippet: it lints clean with the patch, and this repo's test suite passes against the patched ember-estree.