fix(node-resolve): handle browser-mapped paths correctly in nested contexts

[eemeli]

Rollup Plugin Name: node-resolve

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

If yes, then include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers: #919, eemeli/yaml#291

Description

For each entry in a package.json "browser" object entry, the browserMapCache is filled with mapped paths at keys using both the raw source of the path that needs to be remapped, as well as the resolved path. This effectively enables both package name imports (like "foo") as well as relative path imports (like "./foo") to work when doResolveId is called. However, this causes a problem when the raw form of a relative import in a sub-path matches a value that's included in the package.json "browser" entry.

In other words, if "browser" includes "./foo": "./other.js", an import of "./foo" in a file ./bar/baz.js is mapped to ./other.js, even though it shouldn't; the spec is pretty clear on this:

All paths for browser fields are relative to the package.json file location (and usually project root as a result).

To fix, only the resolved paths are checked when applying mappings for relative imports.

[guybedford]

Thanks you for this fix and apologies for the delayed review! This looks great to me.