## Summary
`@tailwindcss/postcss` derives `inputBasePath` from `result.opts.from`:
```ts
let inputFile = result.opts.from ?? ''
let inputBasePath = path.dirname(path.resolve(inputFile))
```
When PostCSS calls the plugin without `from` (some bundlers, including
Turbopack, do this for certain CSS inputs), `inputFile` is `''`,
`path.resolve('')` returns `process.cwd()`, and `path.dirname(...)`
therefore returns the **parent of CWD**. The downstream `compileAst({
base: inputBasePath })` call then asks the resolver to find
`tailwindcss` from one level above the project root, which fails with:
```
Can't resolve 'tailwindcss' in '<parent of CWD>'
```
The plugin already computes `base = opts.base ?? process.cwd()` near the
top. Reusing that as the fallback gives a sensible default (CWD) and
respects an explicit `opts.base` when set.
```diff
-let inputBasePath = path.dirname(path.resolve(inputFile))
+let inputBasePath = inputFile
+ ? path.dirname(path.resolve(inputFile))
+ : base
```
## Test plan
Added a test in `packages/@tailwindcss-postcss/src/index.test.ts` that
processes `@import 'tailwindcss'` via `processor.process(input)` with no
`from` option. Before the fix, this throws `Error: Can't resolve
'tailwindcss' in '<parent of CWD>'`; after the fix, the import resolves
and the processor returns non-empty CSS.
I wasn't able to run the suite locally — `pnpm build` requires `cargo`
for `@tailwindcss/oxide` and I don't have a Rust toolchain set up — so
the test has been written to match existing conventions in
`index.test.ts` (vitest, plain
`postcss([tailwindcss({...})]).process(...)`), and I'm relying on CI to
verify.
---------
Co-authored-by: rebasecase <rebasecase@localhost>
Co-authored-by: Robin Malfait <malfait.robin@gmail.com>
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