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0.19.0: one tool-source resolver for every member, on-request payloads, and a toolchain description library #41
Description
Motivation
Fifteen members declare xlings payloads, and each decides on its own where its tool comes from: some take an option, some an environment variable, rules-spirv and rules-slang fall back to PATH silently (contrary to SPEC build-plugins R6.2), dist-wix and dist-appimage refuse PATH, and rules-cuda, rules-hip, rules-ascendc and dist-apk offer no way to name a tool at all. A tool named in build.mcpp does not prevent the declared payload from being downloaded (mcpp-community/mcpp#755).
Design
Recorded in .agents/docs/2026-10-01-ecosystem-build-plugin-framework-design.md (v3). For 0.19.0, on the engine of mcpp#755:
mcpp.plugins.tool(inplugins-core): one resolver for every member -- atool::choiceoption type (constructible from a string, soo.cmake = "/usr/bin/cmake"keeps working), one priority order (the build program's choice, a member's legacy variable, the engine's override, the payload requested on demand), one refusal text, and a decision recorded with thebuild.mcppline that made it.mcpp.plugins.toolchain(featuretoolchain): builders of a toolchain description for the root build program's toolchain phase (layout,prefixed,compose,from_env_script,with_launcher,managed).- Every member that runs a payload tool migrates to
tool::resolve; members whose tools are needed only for some builds declare their payloadsprovision = "on-request"; the silentPATHfallbacks become warnings. - Documentation and fixtures for each source.
Activity
speak-agent commentedon Oct 1, 2026
Released as 0.19.0
One resolver answers, for every member, where the tool it runs comes from:
mcpp.plugins.tool, in one order — the build program's choice, the member's legacy variable, the engine's override, then the declared payload, asked for there when it is declaredprovision = "on-request".A choice never asks for the payload, which is what makes "the build program names its own tool" mean "the payload is not downloaded". Every answer is recorded with
mcpp::decision, so a build reports the source andmcpp why tool <name>answers from the same record;describe_missingis the one refusal text, listing every way to name the tool.Thirteen members use it: deps-vcpkg, deps-cmake, deps-archive, rules-cuda, rules-hip, rules-sycl, rules-ascendc, rules-slang, rules-spirv, rules-qt, dist-apk, dist-appimage, dist-wix. Five entries are now installed on request:
xim:vcpkg,xim:cmake(twice),xim:appimagetool,xim:bundletool.mcpp.plugins.toolchain(featureplugins-toolchain) builds the statement a root build program makes in a toolchain phase:layout,prefixed,managed,from_env_script,newest_under,env, thewith_*refinements,configure(fn)/use(d).What this release measured in its own CI, beyond the 28
plugin-logiccases and the consumer fixtures:xim:vcpkgno longer appears in the macOS or Windowsrulesjob logs, where main provisionsxim:vcpkg@>=2026.7.27. That saving is also what exposed a defect in the test kit: it left the real build'sMCPP_XPKG_*in the environment, includingpendingfor an on-request payload nothing had asked for, so eight vcpkg cases planned nothing wherever the payload was absent — 19 of 27 on macOS and Windows, 27 of 27 where it was installed. Measured both ways on one binary: 19 → 27.rules-sycl's migration conflated the payload root with the program, so-Lpointed at the compiler's path and the SYCL consumer failed withunable to find library -lsycl. Fixed, and every migrated member audited for the same swap.command -v cmakeanswers a path with no.exe, which the resolver had refused.Engine floor: mcpp 2026.10.1.3 (protocol 15, mcpp-community/mcpp#755).
Released
7f5f0edafter the PR run came back green on all four jobs against the released mcpp 2026.10.1.3 (Linux consumers, macOS rules, Windows rules, Windows deps).v0.19.0, released on GitHub, and mirrored to GitCode (mcpp-res/mcpp-plugins@0.19.0) with the localgtc; the mirrored asset was downloaded back andcmp-verified byte-identical to the GitHub archive, sha2562dd13d81cffd77babdb1070d24659348d2f699c634981f66e3e97206389c5c7e.56990ac), whose workspace matrix rebuilds every member against this version; the index artifact is published, so clients resolve it.qrc_filesfix is in this release rather than displaced by it. Measured before merging: 22 of 23 cases without the fix, with both resource assertions failing, and 23 of 23 with it.Verified against the released artefacts in
xlings subos eco-1001, through the CN mirror, in a privateMCPP_HOME:PASS s755_plugins -- a named cmake is used and the payload is not asked for, alongside the two engine scenarios (3 passed, 0 failed).docs/tool-sources.mdis the reference for both audiences; its chapter 3 gives each way of naming a tool as a completebuild.mcpp, every one of them compiled against this release before being written down.