From e59590e2d69163a128bbcfe7fcb0cf32fbbf2882 Mon Sep 17 00:00:00 2001
From: pat-s <patrick.schratz@gmail.com>
Date: Tue, 30 Jun 2026 13:27:01 +0000
Subject: [PATCH] fix: RcppParallel disable-TBB source patch (env var was a
 no-op) (#106)
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## Summary

Fixes the RcppParallel patch, which was a **no-op** and left the build hanging.

The previous registry entry set `env: { RCPP_PARALLEL_USE_TBB: "0" }`. But `RCPP_PARALLEL_USE_TBB` is a **compile-time `-D` flag** in RcppParallel's Makevars — it is never read from the environment. So the override did nothing: `USE_TBB=Linux` (hardcoded from `uname`) still triggered the **bundled Intel TBB build**, which hangs/fails on musl (Alpine) and newer toolchains (g++ 15 on ubuntu-2604). The `Applying patch …` log only meant the env was set, not that it had any effect.

## Fix

Replace the env entry with a **source patch** (`local/patches/RcppParallel/disable-tbb.patch`) on `src/Makevars.in` that, on Linux:

- leaves `USE_TBB` unset → the whole bundled-TBB build/link path is skipped (no hang), and
- forces `PKG_CXXFLAGS += -DRCPP_PARALLEL_USE_TBB=0` → the sources compile the **TinyThread** backend (needed because `RcppParallel.h` otherwise auto-defaults TBB on for glibc Linux).

## Verification

In a Linux container, applying the patch and running `R CMD INSTALL RcppParallel`:

```
bundled_TBB_build=0      # bundled TBB build never runs
* DONE (RcppParallel)    # installs via TinyThread
```

## Note

bincraft's `apply_source_patch` shells out to `patch`. If a build-env image lacks the `patch` tool (common on Alpine), the patch will report "did not apply cleanly" and fall back to an unpatched (hanging) build. If that happens, the follow-up is to switch bincraft's patch application to `git apply` (git is always present) — happy to do that if needed.

Reviewed-on: https://git.devxy.io/devxy/build-cran-binaries/pulls/106
---
 local/patches/RcppParallel/disable-tbb.patch | 16 ++++++++++++++++
 local/patches/registry.json                  |  6 +++---
 2 files changed, 19 insertions(+), 3 deletions(-)
 create mode 100644 local/patches/RcppParallel/disable-tbb.patch

diff --git a/local/patches/RcppParallel/disable-tbb.patch b/local/patches/RcppParallel/disable-tbb.patch
new file mode 100644
index 0000000..0fe8ad9
--- /dev/null
+++ b/local/patches/RcppParallel/disable-tbb.patch
@@ -0,0 +1,16 @@
+diff --git a/src/Makevars.in b/src/Makevars.in
+index be8445f..faee771 100644
+--- a/src/Makevars.in
++++ b/src/Makevars.in
+@@ -60,7 +60,10 @@ else
+ 	endif
+ 
+ 	ifeq ($(UNAME), Linux)
+-		USE_TBB=Linux
++		# bincraft patch: the bundled Intel TBB build hangs/fails on musl (Alpine)
++		# and newer toolchains (g++ 15). Skip it (leave USE_TBB unset) and force the
++		# TinyThread backend so RcppParallel still builds.
++		PKG_CXXFLAGS += -DRCPP_PARALLEL_USE_TBB=0
+ 	endif
+ 
+ 	ifeq ($(UNAME), SunOS)
diff --git a/local/patches/registry.json b/local/patches/registry.json
index 80460d6..cdeef99 100644
--- a/local/patches/registry.json
+++ b/local/patches/registry.json
@@ -3,10 +3,10 @@
     "package": "RcppParallel",
     "versions": "*",
     "platforms": ["alpine", "ubuntu-2604"],
-    "env": { "RCPP_PARALLEL_USE_TBB": "0" },
+    "env": {},
     "configure_args": [],
     "makevars": {},
-    "patch": null,
-    "reason": "bundled Intel TBB fails to build on musl and on newer toolchains (e.g. g++ 15 on ubuntu-2604); disabling TBB falls back to TinyThread"
+    "patch": "RcppParallel/disable-tbb.patch",
+    "reason": "bundled Intel TBB build hangs/fails on musl (Alpine) and newer toolchains (g++ 15 on ubuntu-2604); patch unsets USE_TBB and forces -DRCPP_PARALLEL_USE_TBB=0 so RcppParallel skips the bundled build and uses the TinyThread backend"
   }
 ]