feat(compat.sycl-runtime): the OpenCL adapter the payload ships is served

pkgs/c/compat.sycl-runtime.lua

@@ -128,29 +128,34 @@ package = {
         c_standard   = "c11",
         sources      = { "mcpp_generated/sycl_runtime_empty.c" },
         targets      = { ["sycl_runtime"] = { kind = "lib" } },
-        -- THE OTHER BACK END THE PAYLOAD SHIPS AN ADAPTER FOR IS DELIBERATELY
-        -- NOT SERVED HERE, and saying so is the point: it was unstated before,
-        -- which is the same condition that let the CUDA one break silently.
+        -- THE OTHER BACK END THE PAYLOAD SHIPS AN ADAPTER FOR.
         --
-        -- `libur_adapter_opencl.so.0` has `libOpenCL.so.1` in its DT_NEEDED and
-        -- nothing on an mcpp artifact's search path provides it, so the OpenCL
-        -- back end of a SYCL program does not load. `compat:opencl` builds that
-        -- loader and would fix it in one line here.
+        -- `libur_adapter_opencl.so.0` has `libOpenCL.so.1` in its DT_NEEDED,
+        -- and nothing on an mcpp artifact's search path provided it, so the
+        -- OpenCL back end of a SYCL program did not load. That is the same
+        -- defect as the missing driver soname one API over, and it was
+        -- invisible for the same reason: an adapter that fails to load is
+        -- reported by nothing.
         --
-        -- MEASURED REASON FOR NOT WRITING THAT LINE. `compat:opencl` depends in
-        -- turn on `compat:opencl-runtime`, a farm of the HOST's proprietary
-        -- OpenCL driver family, so the edge would put a machine-specific vendor
-        -- surface into every SYCL project. It also carries `libnvidia-ml.so.1`,
-        -- and with the edge declared it satisfied the CUDA adapter's need for
-        -- NVML -- which made the farm below look correct while it was not. A
-        -- dependency that hides the defect the package next to it is fixing is
-        -- the wrong dependency.
+        -- A DEPENDENCY RATHER THAN A FARM ENTRY. Unlike the driver, this one is
+        -- not a host file that may not be redistributed: `compat:opencl` builds
+        -- the Khronos ICD loader from source with the canonical soname, and it
+        -- reaches the machine's own drivers through `compat:opencl-runtime`.
+        -- Farming a copy here would be a second answer to a question this index
+        -- already answers.
         --
-        -- A project that wants OpenCL devices from SYCL writes
-        -- `[dependencies.compat] opencl = "2026.05.29"` in its own manifest,
-        -- where the vendor surface is its choice. `tests/farm.cpp` records the
-        -- adapter as expected-unserved so the omission stays visible.
-        deps         = {},
+        -- WHAT WAS BRIEFLY WRITTEN HERE INSTEAD, AND WHY IT WAS WRONG. A draft
+        -- declared the adapter unserved, on the ground that `compat:opencl`
+        -- drags a vendor surface in and that its farm -- which carries
+        -- `libnvidia-ml.so.1` -- made this package's own farm look correct
+        -- while it was missing NVML. The second half was true of a criterion
+        -- that measured the PROCESS: `tests/farm.cpp` now reads each member's
+        -- DT_NEEDED against this farm alone, so nothing else on the search path
+        -- can hide a gap in it. With that fixed, the remaining objection was
+        -- only the size of the surface, and a back end the payload ships an
+        -- adapter for is not something a runtime adapter should leave
+        -- unreachable.
+        deps         = { ["compat.opencl"] = "2026.05.29" },
         runtime = {
             library_dirs = { "mcpp_generated/sycl_runtime/lib" },
             capabilities = { "sycl.runtime" },

tests/examples/sycl-runtime/tests/farm.cpp

@@ -44,12 +44,15 @@
 //     consumer. The entry is present, so the package did its part; the target
 //     is the machine's answer.
 //
-//   * A SONAME this package states it does not serve. Today that is
-//     `libOpenCL.so.1`: the payload ships an OpenCL adapter, and serving it
-//     would mean depending on `compat:opencl`, which drags the host's
-//     proprietary OpenCL driver farm into every SYCL project. The recipe
-//     records that decision; this list is the half that makes it visible, and
-//     a project that wants the back end declares `compat:opencl` itself.
+//   * A SONAME this package gets from a DECLARED DEPENDENCY rather than from
+//     its own farm. Today that is `libOpenCL.so.1`: `compat:sycl-runtime`
+//     depends on `compat:opencl`, whose shared library is deployed beside the
+//     consumer's executable and is found there through `$ORIGIN`. The name is
+//     listed here rather than resolved through the process, because resolving
+//     through the process is what let another farm answer for
+//     `libnvidia-ml.so.1` and hide the gap this test exists to catch. A short
+//     list that a reader can check is the price of a criterion that cannot be
+//     masked.
 //
 // Which devices exist is deliberately NOT asserted: that is the machine's
 // answer, not this package's.
@@ -83,9 +86,14 @@ bool provided_by_the_artifact(const std::string& soname) {
         || soname.rfind("ld-linux", 0) == 0;
 }
 
-// Stated, not served. See the header for the reason and for what a project
-// that wants it writes instead.
-bool declared_unserved(const std::string& soname) {
+// Served by a declared dependency of this package, not by its farm.
+//
+// `compat:opencl` builds the Khronos ICD loader with the canonical soname and
+// mcpp deploys it beside the consumer's executable, where `$ORIGIN` finds it.
+// Naming it here keeps the farm's self-sufficiency assertion exact: everything
+// NOT on this list must be in the farm, and no other directory on the search
+// path can answer for it.
+bool served_by_a_declared_dependency(const std::string& soname) {
     return soname == "libOpenCL.so.1";
 }
 
@@ -258,9 +266,10 @@ int main() {
                                 name.c_str(), soname.c_str());
                 continue;
             }
-            if (declared_unserved(soname)) {
-                std::printf("note %s needs %s, which this package states it "
-                            "does not serve\n", name.c_str(), soname.c_str());
+            if (served_by_a_declared_dependency(soname)) {
+                std::printf("note %s needs %s, which a declared dependency of "
+                            "this package provides\n",
+                            name.c_str(), soname.c_str());
                 continue;
             }
             std::printf("FAIL %s needs %s, which the farm does not carry\n",