nixguix: Add support for listing origins with "recursive" integrity

Without this distinction the current directory or content loader will fail the download
as they currently expect the checksums to be about the tarball. When a recursive
"integrity" is provided, it's actually about the uncompressed tarball as per the
nix-store computation.

It's detailed within the code.

Related to T3294
Related to T3781

swh/lister/nixguix/lister.py

@@ -43,12 +43,33 @@ class ArtifactNatureUndetected(ValueError):
 
 
 class ArtifactNatureMistyped(ValueError):
-    """Raised when a remote artifact's neither a tarball nor a file. It's probably a
-    misconfiguration in the manifest that badly typed a vcs repository."""
+    """Raised when a remote artifact's neither a tarball nor a file.
+
+    Error of this type are' probably a misconfiguration in the manifest generation that
+    badly typed a vcs repository.
+
+    """
 
     pass
 
 
+class ChecksumsComputation(Enum):
+    """The possible artifact types listed out of the manifest."""
+
+    STANDARD = "standard"
+    """Standard checksums (e.g. sha1, sha256, ...) on the tarball or file."""
+    NAR = "nar"
+    """The hash is computed over the NAR archive dump of the output (e.g. uncompressed
+    directory.)"""
+
+
+MAPPING_CHECKSUMS_COMPUTATION = {
+    "flat": ChecksumsComputation.STANDARD,
+    "recursive": ChecksumsComputation.NAR,
+}
+"""Mapping between the outputHashMode from the manifest and how to compute checksums."""
+
+
 @dataclass
 class Artifact:
     """Metadata information on Remote Artifact with url (tarball or file)."""
@@ -61,6 +82,8 @@ class Artifact:
     """List of urls to retrieve tarball artifact if canonical url no longer works."""
     checksums: Dict[str, str]
     """Integrity hash converted into a checksum dict."""
+    checksums_computation: ChecksumsComputation
+    """Checksums computation mode to provide to loaders (e.g. nar, standard, ...)"""
 
 
 @dataclass
@@ -297,7 +320,7 @@ class NixGuixLister(StatelessLister[PageResult]):
                 for url in origin_urls:
                     urlparsed = urlparse(url)
                     if urlparsed.scheme == "":
-                        logger.warning("Missing scheme for <%s>, fallback to http", url)
+                        logger.warning("Missing scheme for <%s>: fallback to http", url)
                         fixed_url = f"http://{url}"
                     else:
                         fixed_url = url
@@ -349,11 +372,23 @@ class NixGuixLister(StatelessLister[PageResult]):
                     chksum_algo: base64.decodebytes(chksum_b64.encode()).hex()
                 }
 
+                # The 'outputHashMode' attribute determines how the hash is computed. It
+                # must be one of the following two values:
+                # - "flat": (default) The output must be a non-executable regular file.
+                #     If it isn’t, the build fails. The hash is simply computed over the
+                #     contents of that file (so it’s equal to what Unix commands like
+                #     `sha256sum` or `sha1sum` produce).
+                # - "recursive": The hash is computed over the NAR archive dump of the
+                #       output (i.e., the result of `nix-store --dump`). In this case,
+                #       the output can be anything, including a directory tree.
+                outputHashMode = artifact.get("outputHashMode", "flat")
+
                 logger.debug("%s: %s", "dir" if is_tar else "cnt", origin)
                 yield ArtifactType.ARTIFACT, Artifact(
                     origin=origin,
                     fallback_urls=fallback_urls,
                     checksums=checksums,
+                    checksums_computation=MAPPING_CHECKSUMS_COMPUTATION[outputHashMode],
                     visit_type="directory" if is_tar else "content",
                 )
             else:
@@ -382,6 +417,7 @@ class NixGuixLister(StatelessLister[PageResult]):
             visit_type=artifact.visit_type,
             extra_loader_arguments={
                 "checksums": artifact.checksums,
+                "checksums_computation": artifact.checksums_computation.value,
                 "fallback_urls": artifact.fallback_urls,
             },
         )

swh/lister/nixguix/tests/data/nixpkgs-swh_sources.json

@@ -38,6 +38,7 @@
     },
     {
       "type": "url",
+      "outputHashMode": "flat",
       "urls": [
         "http://downloads.sourceforge.net/project/nmon/lmon16n.c",
         "http://ufpr.dl.sourceforge.net/project/nmon/lmon16n.c",
@@ -45,6 +46,17 @@
       ],
       "integrity": "sha256-wAEswtkl3ulAw3zq4perrGS6Wlww5XXnQYsEAoYT9fI="
     },
+    {
+      "outputHash": "0s7p9swjqjsqddylmgid6cv263ggq7pmb734z4k84yfcrgb6kg4g",
+      "outputHashAlgo": "sha256",
+      "outputHashMode": "recursive",
+      "type": "url",
+      "urls": [
+        "https://github.com/kandu/trie/archive/1.0.0.tar.gz"
+      ],
+      "integrity": "sha256-j7xp1svMeYIm+WScVe/B7w0jNjMtvkp9a1hLLLlO92g=",
+      "inferredFetcher": "fetchzip"
+    },
     {
       "type": "git",
       "git_url": "https://example.org/pali/0xffff",