- A package can depend on a special patched version of its dependencies.
- The `Spec` YAML (and therefore the hash) now includes the sha256 of
the patch in the `Spec` YAML, which changes its hash.
- The special patched version will be built separately from a "vanilla"
version of the same package.
- This allows packages to maintain patches on their dependencies
without affecting either the dependency package or its dependents.
This could previously be accomplished with special variants, but
having to add variants means the hash of the dependency changes
frequently when it really doesn't need to. This commit allows the
hash to change *just* for dependencies that need patches.
- Patching dependencies shouldn't be the common case, but some packages
(qmcpack, hpctoolkit, openspeedshop) do this kind of thing and it
makes the code structure mirror maintenance responsibilities.
- Note that this commit means that adding or changing a patch on a
package will change its hash. This is probably what *should* happen,
but we haven't done it so far.
- Only applies to `patch()` directives; `package.py` files (and their
`patch()` functions) are not hashed, but we'd like to do that in the
future.
- The interface looks like this: `depends_on()` can optionally take a
patch directive or a list of them:
depends_on(<spec>,
patches=patch(..., when=<cond>),
when=<cond>)
# or
depends_on(<spec>,
patches=[patch(..., when=<cond>),
patch(..., when=<cond>)],
when=<cond>)
- Previously, the `patch()` directive only took an `md5` parameter. Now
it only takes a `sha256` parameter. We restrict this because we want
to be consistent about which hash is used in the `Spec`.
- A side effect of hashing patches is that *compressed* patches fetched
from URLs now need *two* checksums: one for the downloaded archive and
one for the content of the patch itself. Patches fetched uncompressed
only need a checksum for the patch. Rationale:
- we include the content of the *patch* in the spec hash, as that is
the checksum we can do consistently for patches included in Spack's
source and patches fetched remotely, both compressed and
uncompressed.
- we *still* need the patch of the downloaded archive, because we want
to verify the download *before* handing it off to tar, unzip, or
another decompressor. Not doing so is a security risk and leaves
users exposed to any arbitrary code execution vulnerabilities in
compression tools.
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