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[7.2.0] Add a git merge driver for MODULE.bazel.lock (#22650)
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Adds a `jq` script to `scripts/` that merges any number of
`MODULE.bazel.lock` files without using Bazel or reading the
corresponding `MODULE.bazel` files.

The lockfile docs now have a section explaining the steps needed to set
up this script as a custom merger driver for Git, which means that merge
conflicts in `MODULE.bazel.lock` files will always be resolved
automatically. Note that resolution may emit lockfiles with redundant
information that will be dropped by subsequent Bazel invocations.

When Bazel encounters an error during lockfile parsing that could be
caused by a merge conflict, it emits a different error message with a
link to the docs. This required fixing the following kind of server
crash when a conflict marker occurs inside a `recordedFileInputs`
object:
```
FATAL: bazel crashed due to an internal error. Printing stack trace:
java.lang.RuntimeException: Unrecoverable error while evaluating node 'com.google.devtools.build.lib.bazel.bzlmod.BazelLockFileValue$$Lambda/0x000000f8011da998@314cd9ee' (requested by nodes 'RegistryKey{url=https://bcr.bazel.build/}')
	at com.google.devtools.build.skyframe.AbstractParallelEvaluator$Evaluate.run(AbstractParallelEvaluator.java:557)
	at com.google.devtools.build.lib.concurrent.AbstractQueueVisitor$WrappedRunnable.run(AbstractQueueVisitor.java:426)
	at java.base/java.util.concurrent.ForkJoinTask$AdaptedRunnableAction.exec(ForkJoinTask.java:1403)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:387)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1312)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1843)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1808)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:188)
Caused by: java.lang.IllegalArgumentException: the provided path should be absolute in the filesystem
	at com.google.common.base.Preconditions.checkArgument(Preconditions.java:143)
	at com.google.devtools.build.lib.rules.repository.RepoRecordedInput$RepoCacheFriendlyPath.createOutsideWorkspace(RepoRecordedInput.java:202)
	at com.google.devtools.build.lib.rules.repository.RepoRecordedInput$RepoCacheFriendlyPath.parse(RepoRecordedInput.java:222)
	at com.google.devtools.build.lib.rules.repository.RepoRecordedInput$File$1.parse(RepoRecordedInput.java:265)
	at com.google.devtools.build.lib.bazel.bzlmod.GsonTypeAdapterUtil$11.read(GsonTypeAdapterUtil.java:376)
	at com.google.devtools.build.lib.bazel.bzlmod.GsonTypeAdapterUtil$11.read(GsonTypeAdapterUtil.java:367)
	at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41)
	at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:186)
	at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:145)
	at com.google.devtools.build.lib.bazel.bzlmod.DelegateTypeAdapterFactory$1.read(DelegateTypeAdapterFactory.java:133)
	at com.google.devtools.build.lib.bazel.bzlmod.LockFileModuleExtension_GsonTypeAdapter.read(LockFileModuleExtension_GsonTypeAdapter.java:171)
	at com.google.devtools.build.lib.bazel.bzlmod.LockFileModuleExtension_GsonTypeAdapter.read(LockFileModuleExtension_GsonTypeAdapter.java:17)
	at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41)
	at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:187)
	at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:145)
	at com.google.devtools.build.lib.bazel.bzlmod.DelegateTypeAdapterFactory$1.read(DelegateTypeAdapterFactory.java:133)
	at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41)
	at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:187)
	at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:145)
	at com.google.devtools.build.lib.bazel.bzlmod.DelegateTypeAdapterFactory$1.read(DelegateTypeAdapterFactory.java:133)
	at com.google.devtools.build.lib.bazel.bzlmod.BazelLockFileValue_GsonTypeAdapter.read(BazelLockFileValue_GsonTypeAdapter.java:129)
	at com.google.devtools.build.lib.bazel.bzlmod.BazelLockFileValue_GsonTypeAdapter.read(BazelLockFileValue_GsonTypeAdapter.java:15)
	at com.google.gson.Gson.fromJson(Gson.java:991)
	at com.google.gson.Gson.fromJson(Gson.java:956)
	at com.google.gson.Gson.fromJson(Gson.java:905)
	at com.google.gson.Gson.fromJson(Gson.java:876)
	at com.google.devtools.build.lib.bazel.bzlmod.BazelLockFileFunction.getLockfileValue(BazelLockFileFunction.java:93)
	at com.google.devtools.build.lib.bazel.bzlmod.BazelLockFileFunction.compute(BazelLockFileFunction.java:73)
	at com.google.devtools.build.skyframe.AbstractParallelEvaluator$Evaluate.run(AbstractParallelEvaluator.java:468)
	... 7 more
```

Alternatives considered:
* Letting Bazel resolve the conflict would require building knowledge
about particular version control systems and their conflict style into
Bazel. It would also either require the user to resolve conflicts in
`MODULE.bazel` first or deviate from the current behavior that the
lockfile is not updated when any Bzlmod error is encountered. The jq
script can be used as is by every VCS with merge driver support and
resolves the conflict in `MODULE.bazel.lock` independently of
`MODULE.bazel`.
* Implementing the git merge driver as a `bazel mod` subcommand. This
could be the source of intransparent slowdowns during regular git
operations, which may even be triggered by other tools such as IDEs. The
jq script is very fast.
* Implementing the merger as a Go binary in buildtools would replace the
ubiquitous jq tool with a special purpose binary while also not solving
the problem that per-user action is required once to register a custom
merge driver.

Implements
https://docs.google.com/document/d/1TjA7-M5njkI1F38IC0pm305S9EOmxcUwaCIvaSmansg/edit#heading=h.5mcn15i0e1ch

RELNOTES: Git merge conflicts in `MODULE.bazel.lock` files can be
resolved automatically. See
https://bazel.build/external/lockfile#automatic-resolution for the
required setup.

Closes #22428.

PiperOrigin-RevId: 640596606
Change-Id: I20659e3e53a7d8f2529f2ad5a3e7f258d7af026d

Commit
3187250

Co-authored-by: Fabian Meumertzheim <fabian@meumertzhe.im>
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bazel-io and fmeum authored Jun 5, 2024
1 parent 0308f42 commit 691149a
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24 changes: 24 additions & 0 deletions MODULE.bazel
Original file line number Diff line number Diff line change
Expand Up @@ -307,6 +307,30 @@ gvm.graalvm(
)
use_repo(gvm, "graalvm_toolchains")

http_file = use_repo_rule("@bazel_tools//tools/build_defs/repo:http.bzl", "http_file")

# DO NOT UPDATE the jq version, this is used to verify compatibility with old versions.
http_file(
name = "jq_linux_amd64",
executable = True,
integrity = "sha256-xrOn19PntwxvUbcGo7kL0BgzhGxU0yyjLwAn8AIm/20=",
urls = ["https://github.com/jqlang/jq/releases/download/jq-1.5/jq-linux64"],
)

http_file(
name = "jq_macos_amd64",
executable = True,
integrity = "sha256-OG6SyYKlb+SFFGjXqTHfyilWDO4wag5mxqG9QGXT2sU=",
urls = ["https://github.com/jqlang/jq/releases/download/jq-1.5/jq-osx-amd64"],
)

http_file(
name = "jq_windows_amd64",
executable = True,
integrity = "sha256-6+zYQLpH779mgihoF4zHIaFRBgk396xAbj0xvQFb3pQ=",
urls = ["https://github.com/jqlang/jq/releases/download/jq-1.5/jq-win64.exe"],
)

# =========================================
# Other Bazel testing dependencies
# =========================================
Expand Down
87 changes: 79 additions & 8 deletions MODULE.bazel.lock

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26 changes: 26 additions & 0 deletions scripts/BUILD
Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,32 @@ sh_test(
],
)

filegroup(
name = "jq",
srcs = select({
"@platforms//os:linux": ["@jq_linux_amd64//file"],
"@platforms//os:macos": ["@jq_macos_amd64//file"],
"@platforms//os:windows": ["@jq_windows_amd64//file"],
}),
)

sh_test(
name = "bazel_lockfile_merge_test",
size = "small",
srcs = ["bazel_lockfile_merge_test.sh"],
data = [
"bazel-lockfile-merge.jq",
"testenv.sh",
":jq",
"//src/test/shell:bashunit",
"//src/test/tools/bzlmod:MODULE.bazel.lock",
"@bazel_tools//tools/bash/runfiles",
],
env = {
"JQ_RLOCATIONPATH": "$(rlocationpath :jq)",
},
)

filegroup(
name = "srcs",
srcs = glob(["**"]) + [
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54 changes: 54 additions & 0 deletions scripts/bazel-lockfile-merge.jq
Original file line number Diff line number Diff line change
@@ -0,0 +1,54 @@
# Merges an arbitrary number of MODULE.bazel.lock files.
#
# Input: an array of MODULE.bazel.lock JSON objects (as produced by `jq -s`).
# Output: a single MODULE.bazel.lock JSON object.
#
# This script assumes that all files are valid JSON and have a numeric
# "lockFileVersion" field. It will not fail on any such files, but only
# preserves information for files with a version of 10 or higher.
#
# The first file is considered to be the base when deciding which values to
# keep in case of conflicts.

# Like unique, but preserves the order of the first occurrence of each element.
def stable_unique:
reduce .[] as $item ([]; if index($item) == null then . + [$item] else . end);

# Given an array of objects, shallowly merges the result of applying f to each
# object into a single object, with a few special properties:
# 1. Values are uniquified before merging and then merged with last-wins
# semantics. Assuming that the first value is the base, this ensures that
# later occurrences of the base value do not override other values. For
# example, when this is called with B A1 A2 and A1 contains changes to a
# field but A2 does not (compared to B), the changes in A1 will be preserved.
# 2. Object keys on the top level are sorted lexicographically after merging,
# but are additionally split on ":". This ensures that module extension IDs,
# which start with labels, sort as strings in the same way as they due as
# structured objects in Bazel (that is, //python/extensions:python.bzl
# sorts before //python/extensions/private:internal_deps.bzl).
def shallow_merge(f):
map(f) | stable_unique | add | to_entries | sort_by(.key | split(":")) | from_entries;

(
# Ignore all MODULE.bazel.lock files that do not have the maximum
# lockFileVersion.
(map(.lockFileVersion) | max) as $maxVersion
| map(select(.lockFileVersion == $maxVersion))
| {
lockFileVersion: $maxVersion,
registryFileHashes: shallow_merge(.registryFileHashes),
selectedYankedVersions: shallow_merge(.selectedYankedVersions),
# Group extension results by extension ID across all lockfiles with
# shallowly merged factors map, then shallowly merge the results.
moduleExtensions: (map(.moduleExtensions | to_entries)
| flatten
| group_by(.key)
| shallow_merge({(.[0].key): shallow_merge(.value)}))
}
)? //
# We get here if the lockfiles with the highest lockFileVersion could not be
# processed, for example because all lockfiles have lockFileVersion < 10.
# In this case Bazel 7.2.0+ would ignore all lockfiles, so we might as well
# return the first lockfile for the proper "mismatched version" error
# message.
.[0]
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