2026.9.27.1: a member reached as a path dependency of the workspace root's package cannot use workspace = true

Since 2026.9.27.1 (#714), a workspace member reached as a path dependency of the workspace root's own package can no longer use workspace = true: the build fails with "no workspace declares" the dependency, although the root's [workspace.dependencies] declares it and [workspace].members lists the member. 2026.9.26.1 builds the same tree.

Reproduction

root/
  mcpp.toml
  src/main.cpp          import a; int main() { return a_value() - 1; }
  a/mcpp.toml
  a/src/a.cppm          export module a; export int a_value() { return 1; }

root/mcpp.toml:

[workspace]
members = ["a"]

[workspace.dependencies]
cmdline = "0.0.2"

[package]
name    = "root"
version = "0.1.0"

[dependencies]
a = { path = "a" }

root/a/mcpp.toml:

[package]
name    = "a"
version = "0.1.0"

[targets.a]
kind = "lib"

[dependencies]
cmdline.workspace = true

[lib]
path = "src/a.cppm"

mcpp build in root/:

2026.9.26.1: Compiling a (path) … Finished.
2026.9.27.1:

error: dependency 'a': <root>/a/mcpp.toml: [dependencies] cmdline = { workspace = true }, but no workspace declares 'cmdline'.
       `workspace = true` is resolved against the [workspace.dependencies] of the workspace whose `members` list this package.
       fix: list this package in that workspace's [workspace] members, or state the dependency's version, path or git source here.

a is listed in that workspace's members, so the fix the message suggests is already in place. Building inside root/a/ works with 2026.9.27.1; mcpp build -p a at the root answers workspace member 'a' not found in [workspace].members.

Impact

Sunrisepeak/mcpp-language-server is laid out this way (root package = the server, modules/base and modules/platform are members it depends on by path, each using openkal-llvm-runtime.workspace = true), and does not build with 2026.9.27.1. Its CI pins 2026.9.26.1, so this shows up first in its nightly run against the latest mcpp.

Related: #713, #714.

Implemented in 2026.9.28.1 (#727). The triage is in .agents/docs/2026-09-27-eight-reports-by-home-and-one-optimisation-plan.md §2.

The workspace context follows the manifest position. A rooted workspace (a root with both [package] and [workspace]) now carries its context to a member reached through the root's own [dependencies] path entry. The member inherits [workspace.package] and [workspace.build] and resolves workspace = true against [workspace.dependencies], as SPEC-004 §9 item 1 states. [toolchain], [target.<triple>] and [indices] stay the root's.
-p, --package <NAME> resolves by package identity. One resolver (resolve_member_dir) answers in this order: the qualified name, the package name, then the member's path or directory name. Paths are compared as paths. A package name that two namespaces share is refused, with both qualified names given. A value that is one member's package name and another member's directory selects the package, with a warning.

Verification of the published release. A fresh SubOS sandbox (xlings subos use <name> --sandbox) with the CN mirror configured for both xlings and mcpp installed mcpp@2026.9.28.1 through the index and ran one script over the published binary: 13 ok, 0 failed (the Windows-only items are reported as not run). The same script in a second sandbox against mcpp@2026.9.27.1 reads 5 ok, 8 failed, so each assertion below measures this change rather than the setup it runs in.

criterion	2026.9.28.1	2026.9.27.1
the member builds with `[workspace.build]` flags; `mcpp.lock` records the pinned `cmdline` 0.0.1, not 0.0.2	ok	`missing required field 'package.version'`
`-p wsa` selects the member whose package is `wsa` in directory `a`	ok	`workspace member 'wsa' not found`

e2e 805 and 806 carry the same properties in the suite.

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2026.9.27.1: a member reached as a path dependency of the workspace root's package cannot use workspace = true #725

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2026.9.27.1: a member reached as a path dependency of the workspace root's package cannot use workspace = true #725

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speak-agent commented on Sep 27, 2026

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