…emit (#92292)

### What?

Adds deduplication and conflict detection to the asset emission stage in
`crates/next-core/src/emit.rs`, and a new `IssueStage::Emit` variant in
`turbopack-core`.

Before emitting, assets are grouped by their output path. If multiple
assets map to the same path:

- If their content is identical, one is silently chosen (deduplication).
- If their content differs, both versions are written to
`<node_root>/<content_hash>.<ext>` and an `EmitConflictIssue` is raised
for each conflict. All assets are still emitted — conflicts do not abort
the build.

### Why?

Previously, duplicate output assets for the same path were emitted
unconditionally — whichever write happened last silently won. This
masked build graph bugs where two different modules produced conflicting
output files. Reporting conflicts as issues (rather than silently
overwriting) makes them visible and easy to diagnose without breaking
the build.

### How?

- Collect all assets with their resolved paths via `try_flat_join`.
- Bucket them into two `FxIndexMap<FileSystemPath,
Vec<ResolvedVc<Box<dyn OutputAsset>>>>` — one for node-root assets and
one for client assets.
- For each bucket entry, call `check_duplicates`: compare every asset
against the first using `assets_diff`. If content differs, emit an
`EmitConflictIssue` as a turbo-tasks collectible — but still return the
first asset so emission continues.
- `assets_diff` is a `#[turbo_tasks::function]` that takes only
`(asset1, asset2, extension, node_root)` — the `asset_path` stays out of
the task key to avoid unnecessary task cardinality. When file content
differs, it hashes each version with xxh3, writes them to
`<node_root>/<hash>.<ext>`, and returns the paths in the detail message
so the user can diff them.
- `EmitConflictIssue` implements the `Issue` trait with
`IssueStage::Emit` (new variant added to `turbopack-core`),
`IssueSeverity::Error`, a descriptive title, and a detail message
explaining the type of conflict.
- Node-root and client assets are emitted in parallel via
`futures::join!` (not `try_join!`) to ensure deterministic error
reporting — both branches always run to completion so errors are
reported in a consistent order.

---------

Co-authored-by: Tobias Koppers <[email protected]>
Co-authored-by: Claude <[email protected]>

…emit (#92292)

### What?

Adds deduplication and conflict detection to the asset emission stage in
`crates/next-core/src/emit.rs`, and a new `IssueStage::Emit` variant in
`turbopack-core`.

Before emitting, assets are grouped by their output path. If multiple
assets map to the same path:

- If their content is identical, one is silently chosen (deduplication).
- If their content differs, both versions are written to
`<node_root>/<content_hash>.<ext>` and an `EmitConflictIssue` is raised
for each conflict. All assets are still emitted — conflicts do not abort
the build.

### Why?

Previously, duplicate output assets for the same path were emitted
unconditionally — whichever write happened last silently won. This
masked build graph bugs where two different modules produced conflicting
output files. Reporting conflicts as issues (rather than silently
overwriting) makes them visible and easy to diagnose without breaking
the build.

### How?

- Collect all assets with their resolved paths via `try_flat_join`.
- Bucket them into two `FxIndexMap<FileSystemPath,
Vec<ResolvedVc<Box<dyn OutputAsset>>>>` — one for node-root assets and
one for client assets.
- For each bucket entry, call `check_duplicates`: compare every asset
against the first using `assets_diff`. If content differs, emit an
`EmitConflictIssue` as a turbo-tasks collectible — but still return the
first asset so emission continues.
- `assets_diff` is a `#[turbo_tasks::function]` that takes only
`(asset1, asset2, extension, node_root)` — the `asset_path` stays out of
the task key to avoid unnecessary task cardinality. When file content
differs, it hashes each version with xxh3, writes them to
`<node_root>/<hash>.<ext>`, and returns the paths in the detail message
so the user can diff them.
- `EmitConflictIssue` implements the `Issue` trait with
`IssueStage::Emit` (new variant added to `turbopack-core`),
`IssueSeverity::Error`, a descriptive title, and a detail message
explaining the type of conflict.
- Node-root and client assets are emitted in parallel via
`futures::join!` (not `try_join!`) to ensure deterministic error
reporting — both branches always run to completion so errors are
reported in a consistent order.

---------

Co-authored-by: Tobias Koppers <[email protected]>
Co-authored-by: Claude <[email protected]>

…emit (#92292)

Adds deduplication and conflict detection to the asset emission stage in
`crates/next-core/src/emit.rs`, and a new `IssueStage::Emit` variant in
`turbopack-core`.

Before emitting, assets are grouped by their output path. If multiple
assets map to the same path:

- If their content is identical, one is silently chosen (deduplication).
- If their content differs, both versions are written to
`<node_root>/<content_hash>.<ext>` and an `EmitConflictIssue` is raised
for each conflict. All assets are still emitted — conflicts do not abort
the build.

Previously, duplicate output assets for the same path were emitted
unconditionally — whichever write happened last silently won. This
masked build graph bugs where two different modules produced conflicting
output files. Reporting conflicts as issues (rather than silently
overwriting) makes them visible and easy to diagnose without breaking
the build.

- Collect all assets with their resolved paths via `try_flat_join`.
- Bucket them into two `FxIndexMap<FileSystemPath,
Vec<ResolvedVc<Box<dyn OutputAsset>>>>` — one for node-root assets and
one for client assets.
- For each bucket entry, call `check_duplicates`: compare every asset
against the first using `assets_diff`. If content differs, emit an
`EmitConflictIssue` as a turbo-tasks collectible — but still return the
first asset so emission continues.
- `assets_diff` is a `#[turbo_tasks::function]` that takes only
`(asset1, asset2, extension, node_root)` — the `asset_path` stays out of
the task key to avoid unnecessary task cardinality. When file content
differs, it hashes each version with xxh3, writes them to
`<node_root>/<hash>.<ext>`, and returns the paths in the detail message
so the user can diff them.
- `EmitConflictIssue` implements the `Issue` trait with
`IssueStage::Emit` (new variant added to `turbopack-core`),
`IssueSeverity::Error`, a descriptive title, and a detail message
explaining the type of conflict.
- Node-root and client assets are emitted in parallel via
`futures::join!` (not `try_join!`) to ensure deterministic error
reporting — both branches always run to completion so errors are
reported in a consistent order.

---------

Co-authored-by: Tobias Koppers <[email protected]>
Co-authored-by: Claude <[email protected]>