fix(html): correct relative link depth on default-module subpages

[crowlbot]

Problem

When HTML docs are generated for a package with multiple entrypoints, the pages for symbols belonging to the default/main module contain broken relative links: stylesheets fail to load, search-result links 404, and cross-links lose the base path. See #717 and #685.

For example, a symbol page rendered for the main module links back to the root with ../ when it actually needs ../../, so links like ~/Foo.html resolve to /~/Foo.html (missing a path segment) and 404.

Cause

Symbol pages are always written to {short_path.path}/~/{name}.html, for every module including the main entrypoint (src/html/mod.rs). But href_path_resolve hard-coded the main entrypoint to a directory depth of 1 when computing the ../ prefix:

UrlResolveKind::Symbol { file, .. } => "../".repeat(if file.is_main {
  1
} else {
  file.path.split('/').count() + 1
}),

That is only correct when the main module's path is . (the common single-package case, where the page lives at ./~/Foo.html). When several entrypoints share a common ancestor, the main module gets a real path such as index.ts, so its symbol pages live at index.ts/~/Foo.html — two directories deep — but were still linked back to the root with a single ../. This also explains why #685 saw the bug depend on entrypoint ordering: it changes which module becomes the default and what path it gets.

Fix

Compute the depth from the actual number of segments in file.path, treating . as zero segments (it adds no directory). This unifies the main and non-main cases:

• main module at . → symbol page ./~/Foo.html → ../ (unchanged)
• main module at index.ts → symbol page index.ts/~/Foo.html → ../../ (fixed)
• non-main module at foo → foo/~/Bar.html → ../../ (unchanged)

Added unit tests in src/html/util.rs pinning all three cases; the full html_test snapshot suite is unaffected.

Fixes #717

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}