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bazel/avro: make avrogen header include guard deterministic #30487

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bazel/avro: make avrogen header include guard deterministic #30487

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5 changes: 3 additions & 2 deletions MODULE.bazel.lock
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1 change: 1 addition & 0 deletions bazel/repositories.bzl
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@ def data_dependency():
patches = [
"//bazel/thirdparty:avro-snappy-includes.patch",
"//bazel/thirdparty:avro-fmt-const.patch",
"//bazel/thirdparty:avrogen-stable-include-guard.patch",
],
patch_args = ["-p1"],
)
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28 changes: 28 additions & 0 deletions bazel/thirdparty/avrogen-stable-include-guard.patch
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Original file line number Diff line number Diff line change
@@ -0,0 +1,28 @@
From: Travis Downs <travis.downs@redpanda.com>
Subject: [PATCH] avrogencpp: use deterministic include guard

The generated header's include guard was suffixed with the output of a
`boost::mt19937` seeded from `::time(nullptr)`, which produced a different
guard on every avrogen invocation. That made every consumer of the generated
header (e.g. `manifest_list_avro.cc`) see a different input digest on each
build, breaking Bazel's remote cache for the entire dependency chain even
on byte-identical schemas.

`headerFile_` is already a unique-per-output path; `makeCanonical(h, true)`
canonicalizes it into a valid identifier ending in `_H` (from the `.h`
extension). Dropping the random number leaves a stable, still-unique guard.

Tracks CORE-16317.

diff --git a/lang/c++/impl/avrogencpp.cc b/lang/c++/impl/avrogencpp.cc
--- a/lang/c++/impl/avrogencpp.cc
+++ b/lang/c++/impl/avrogencpp.cc
@@ -793,7 +793,7 @@
string CodeGen::guard() {
string h = headerFile_;
makeCanonical(h, true);
- return h + "_" + lexical_cast<string>(random_()) + "_H";
+ return h + "_H";
}

void CodeGen::generate(const ValidSchema &schema) {
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