Analysis: Improve how render calls resolve to partials

[marcoroth]

This pull request teaches the partial index about Rails' view_paths instead of a single guessed root, and stops discarding templates that Rails will render but the globs do not match.

Running herb actionview check against a large application reported 118 unresolved render calls. Most of them pointed at partials that exist on disk. Two causes, both ours.

The first is a template that carries a handler but no format. Rails reads a filename as name.format.handler, and the format segment is optional, so _icon.erb is a real partial that Rails serves for any format. PartialResolution::EXTENSIONS already agrees, and the filesystem walk already finds it. PartialIndex#build_with_config then replaced that walk with the linter's file list, whose globs enumerate HTML formats (**/*.html.erb, **/*.html, **/*.rhtml), and every such partial vanished from the index.

The config's globs still decide what the linter and formatter look at. The index just keeps what the walk found.

The second is that a Rails application has an ordered list of view paths, not one. The application comes first, then each engine, then anything pushed on at runtime, and a name resolves against each in turn. The index held a single view_root and derived every partial name relative to it, so a template under an engine could not be named at all and was silently skipped.

PartialIndex now takes the list, in precedence order:

PartialIndex::new(view_roots: &[PathBuf], templates: Vec<String>)

PartialIndex.new(view_roots, templates)

new PartialIndex(viewRoots: string[], declarations)

The shared primitive reports which root matched, so position can order two partials that share a name. An earlier view path shadows a later one, which extension precedence alone could not express, and a sibling render resolves within the root that owns the calling template.

check gained a section for templates whose filename omits the format, since these resolve in Rails but are easy to write by accident:

 Templates without a format:
 Rails reads a template filename as `name.format.handler`. Without a format it matches every one.

   ! app/views/shared/_icon.erb
   ! app/views/layouts/admin.erb
   ! app/views/user_mailer/signup.erb

Both entry points and partials appear, because a formatless mailer view is a template in both directions: we were failing to resolve into these files and failing to walk out of them.

render "layouts/page.html.erb" names a partial that exists, but the extension is part of the name, so appending another one never matched. The file was reported as unresolved at the call site and as unused at the same time. Resolution now strips a known template extension from the name first.

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☁️ Nx Cloud last updated this comment at 2026-08-15 16:18:25 UTC

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