Making a tool exportable

How to make a tool exportable with the export goal.

---

Backends that implement the export goal can indicate binaries that should be exported. These will have their contents exported to a subfolder in the dist/bins directory, and the binary itself will be linked in dist/bin.

Downloadable Tools

Subclasses of ExternalTool (including TemplatedExternalTool) have the logic for exporting implemented. Tools are marked for export as follows:

1. Implement ExternalTool.generate_exe if the default is not correct. For instance, a tool downloaded might include a binary, a readme, and a license. This method will point to the binary within the downloaded files.

2. Register a UnionRule with ExportableTool. For example, UnionRule(ExportableTool, FortranLint)

Implementing for new backends

Backends need to implement:

1. A subclass of ExportRequest

@dataclass(frozen=True)
class ExportExternalToolRequest(ExportRequest):
    pass

2. A rule from this subclass to ExportResults

@rule
async def export_external_tools(
    request: ExportExternalToolRequest, export: ExportSubsystem
) -> ExportResults:

3. Inside of that rule, fill the ExportResult.exported_binaries field.

ExportResult(
    description=f"Export tool {req.resolve}",
    reldir=dest,
    digest=downloaded_tool.digest,
    resolve=req.resolve,
    exported_binaries=(ExportedBinary(name=Path(exe).name, path_in_export=exe),),
)

4. For every tool, mark it for export registering a UnionRule with ExportableTool.

def rules():
    return [
        ...,
        `UnionRule(ExportableTool, FortranLint)`,
    ]