Bazel: add LFS rules

misc/bazel/internal/git_lfs_smudge.py

@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+
+import sys
+import pathlib
+import subprocess
+import os
+
+sources = [pathlib.Path(arg).resolve() for arg in sys.argv[1:]]
+source_dir = pathlib.Path(os.path.commonpath(src.parent for src in sources))
+
+for src in sources:
+    with open(src, 'rb') as input:
+        lfs_pointer = subprocess.run(["git", "lfs", "clean", "--", src],
+                                     stdin=input, stdout=subprocess.PIPE, check=True, cwd=source_dir).stdout
+    with open(src.name, 'wb') as output:
+        subprocess.run(["git", "lfs", "smudge", "--", src], input=lfs_pointer, stdout=output, check=True, cwd=source_dir)

misc/bazel/lfs.bzl

@@ -0,0 +1,73 @@
+def _smudge(repository_ctx, srcs):
+    for src in srcs:
+        repository_ctx.watch(src)
+    script = Label("//misc/bazel/internal:git_lfs_smudge.py")
+    python = repository_ctx.which("python3") or repository_ctx.which("python")
+    if not python:
+        fail("Neither python3 nor python executables found")
+    res = repository_ctx.execute([python, script] + srcs, quiet = False)
+    if res.return_code != 0:
+        fail("git LFS smudging failed while instantiating @%s" % repository_ctx.name)
+
+def _download_and_extract_lfs(repository_ctx):
+    attr = repository_ctx.attr
+    src = repository_ctx.path(attr.src)
+    if attr.build_file_content and attr.build_file:
+        fail("You should specify only one among build_file_content and build_file for rule @%s" % repository_ctx.name)
+    _smudge(repository_ctx, [src])
+    repository_ctx.extract(src.basename, stripPrefix = attr.strip_prefix)
+    repository_ctx.delete(src.basename)
+    if attr.build_file_content:
+        repository_ctx.file("BUILD.bazel", attr.build_file_content)
+    elif attr.build_file:
+        repository_ctx.symlink(attr.build_file, "BUILD.bazel")
+
+def _download_lfs(repository_ctx):
+    attr = repository_ctx.attr
+    if int(bool(attr.srcs)) + int(bool(attr.dir)) != 1:
+        fail("Exactly one between `srcs` and `dir` must be defined for @%s" % repository_ctx.name)
+    if attr.srcs:
+        srcs = [repository_ctx.path(src) for src in attr.srcs]
+    else:
+        dir = repository_ctx.path(attr.dir)
+        if not dir.is_dir:
+            fail("`dir` not a directory in @%s" % repository_ctx.name)
+        srcs = [f for f in dir.readdir() if not f.is_dir]
+    _smudge(repository_ctx, srcs)
+
+    # with bzlmod the name is qualified with `~` separators, and we want the base name here
+    name = repository_ctx.name.split("~")[-1]
+    repository_ctx.file("BUILD.bazel", """
+exports_files({files})
+
+filegroup(
+    name = "{name}",
+    srcs = {files},
+    visibility = ["//visibility:public"],
+)
+""".format(name = name, files = repr([src.basename for src in srcs])))
+
+lfs_archive = repository_rule(
+    doc = "Export the contents from an on-demand LFS archive. The corresponding path should be added to be ignored " +
+          "in `.lfsconfig`.",
+    implementation = _download_and_extract_lfs,
+    attrs = {
+        "src": attr.label(mandatory = True, doc = "Local path to the LFS archive to extract."),
+        "build_file_content": attr.string(doc = "The content for the BUILD file for this repository. " +
+                                                "Either build_file or build_file_content can be specified, but not both."),
+        "build_file": attr.label(doc = "The file to use as the BUILD file for this repository. " +
+                                       "Either build_file or build_file_content can be specified, but not both."),
+        "strip_prefix": attr.string(default = "", doc = "A directory prefix to strip from the extracted files. "),
+    },
+)
+
+lfs_files = repository_rule(
+    doc = "Export LFS files for on-demand download. Exactly one between `srcs` and `dir` must be defined. The " +
+          "corresponding paths should be added to be ignored in `.lfsconfig`.",
+    implementation = _download_lfs,
+    attrs = {
+        "srcs": attr.label_list(doc = "Local paths to the LFS files to export."),
+        "dir": attr.label(doc = "Local path to a directory containing LFS files to export. Only the direct contents " +
+                                "of the directory are exported"),
+    },
+)