ww test: omit marker for empty list results

docs/build-system.md

@@ -7628,6 +7628,149 @@ unchanged artifact and binary bytes; build/no-test/compile-only/rejection
 nonexecution; unchanged raw/direct compatibility; exact tool locale/TMPDIR; and
 stage, transaction, capture, and workdir cleanup.
 
+### 11.37 Implemented empty list-mode output
+
+A valid directory-owned `ww test -list` request now emits one qualified test
+name per selected descriptor and emits no harness list bytes when its filters
+select zero tests. The test product still starts, package initialization still
+runs, the harness returns success without accounting, and the coordinator still
+emits the normal package `ok` result. Ordinary non-list execution with zero
+selected tests remains distinct: it keeps `[no matches]` and its
+discovered/selected/started/completed accounting.
+
+#### Pinned Go evidence and fact classification
+
+The sole authority is official Go 1.26.5 at commit
+`c19862e5f8415b4f24b189d065ed739517c548ba`:
+
+- `cmd/go` registers `-list` among the flags forwarded to the test binary
+  ([`cmd/go/internal/test/testflag.go`, function `init`, lines 32–80](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/internal/test/testflag.go#L32-L80)).
+- `testing.(*M).Run` calls `listTests`, sets exit code 0, and returns before the
+  ordinary test execution and no-tests warning
+  ([`testing/testing.go`, lines 2407–2411](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/testing/testing.go#L2407-L2411)
+  and [2440–2458](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/testing/testing.go#L2440-L2458)).
+- `listTests` validates the pattern and prints only inside successful match
+  branches. It has no zero-match output branch
+  ([`testing/testing.go`, function `listTests`, lines 2509–2535](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/testing/testing.go#L2509-L2535)).
+- `testShowPass` retains successful list output, while the successful run actor
+  adds a no-tests suffix only if the captured bytes contain the ordinary
+  no-tests warning
+  ([`cmd/go/internal/test/test.go`, function `testShowPass`, lines 649–652](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/internal/test/test.go#L649-L652)
+  and method `(*runTestActor).Act`, lines 1706–1732](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/internal/test/test.go#L1706-L1732)).
+- Official `list_test_simple.txt` asserts that list mode emits the matching Test,
+  Benchmark, and Example names
+  ([`cmd/go/testdata/script/list_test_simple.txt`, lines 3–14](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/go/testdata/script/list_test_simple.txt#L3-L14)).
+
+Those source branches and official positive assertions are behavior directly
+implemented or asserted by pinned Go. That a zero-match `go test -list` run has
+no list payload, avoids the ordinary no-tests warning, and may still receive the
+command's normal successful package result is behavior derived from their
+composition. WW retains its local `-list` plus `-run`/`-filter` syntax; only the
+applicable selected-name and empty-result behavior is aligned.
+
+#### Fresh four-axis audit and direct pre-fix measurements
+
+The bounded audit examined all four permanent axes before selecting this test
+runtime difference:
+
+- **Go-like build:** pinned `(*ErrorReporter).errorUnresolved` gives a missing
+  `main.main` a dedicated failure
+  ([`cmd/link/internal/ld/errors.go`, lines 29–67](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/link/internal/ld/errors.go#L29-L67)),
+  asserted by `TestUndefinedRelocErrors` and official `issue10978`
+  ([`cmd/link/internal/ld/ld_test.go`, lines 19–45](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/link/internal/ld/ld_test.go#L19-L45),
+  [`testdata/issue10978/main.go`, lines 5–27](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/link/internal/ld/testdata/issue10978/main.go#L5-L27)).
+  Both WW stages rejected a selected command package without `fn main`, emitted
+  zero stdout and the same 50 stderr bytes (SHA-256
+  `9ed4d7684412c6d2e615041902072c81e9e09acb3970246d89a2c8bdddd2fcfa`),
+  and published no output. This audited applicable property was aligned.
+- **Go-like test:** for a directory containing one `visible` test, both stages
+  ran `test -list -run no_such_test`, exited 0 with empty stderr, and emitted the
+  same 78 stdout bytes (SHA-256
+  `d59638ab03a27803ca8e3fd884f341bbb1535ec9604fb69bdff1de4f608a8da0`):
+  `[no matches]\n` followed by the normal package result. Positive list
+  selection printed `list_nomatch.visible` once in both stages. This synthetic
+  empty-result line was the selected difference.
+- **Go-like package:** pinned `MultiplePackageError` and directory scanning
+  reject conflicting declarations
+  ([`go/build/build.go`, lines 538–549](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/go/build/build.go#L538-L549)
+  and [939–967](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/go/build/build.go#L939-L967)),
+  asserted by `TestMultiplePackageImport` and official `testdata/multi`
+  ([`go/build/build_test.go`, lines 105–133](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/go/build/build_test.go#L105-L133)).
+  Both WW stages rejected an `alpha`/`beta` directory with zero stdout and the
+  same 159 stderr bytes (SHA-256
+  `eaaa0c91f41b5d3deac4caf4299d5c7c650a1330be9b43edd090b8bfea906076`).
+  This audited applicable property was aligned.
+- **Go-like import:** pinned `unusedImports` and `errorUnusedPkg` reject a
+  nonblank unused alias
+  ([`cmd/compile/internal/types2/resolver.go`, lines 706–740](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/cmd/compile/internal/types2/resolver.go#L706-L740)),
+  asserted by official `importdecl0`
+  ([`internal/types/testdata/check/importdecl0/importdecl0a.go`, lines 9–26](https://github.com/golang/go/blob/c19862e5f8415b4f24b189d065ed739517c548ba/src/internal/types/testdata/check/importdecl0/importdecl0a.go#L9-L26)).
+  Both WW stages rejected an unused `spare` alias for dotted import `dep` with
+  zero stdout and the same diagnostic after only private scratch-PID
+  normalization (SHA-256
+  `a429b027e92d52de1c5ec581b1f45c860b0e85b459c3ac7347e2719900cec511`).
+  This audited applicable property was aligned without changing dotted import
+  identity.
+
+The command observations and byte hashes are directly measured WW behavior.
+The linked source branches and testdata assertions are behavior directly
+implemented or asserted by pinned Go. Applying the empty-list rule to WW's one
+local directory-owned test product while retaining its manifest-free input and
+filter syntax is behavior derived from that pinned execution boundary.
+
+Pre-fix `test -c` products were byte-identical between Cstage and WWstage:
+112829 bytes, SHA-256
+`d2994ef440d7ceb9be0a7caf53c90dd19d208e847e51ff41ecb89504f825c4c8`.
+Directly running either retained product with the same nonmatching list filter
+already emitted no stdout or stderr because it had no coordinator-supplied
+package prefix. Explicit raw-file requests with package options remained a
+separate rejected CLI shape in both stages.
+
+#### Ownership, final behavior, and preserved boundaries
+
+`lib/test.run` is the semantic owner. Its existing descriptor loop still
+qualifies, filters, and prints every positive list match in order; its list
+return now emits nothing extra when the selected count is zero. The package
+coordinator does not recognize or strip a magic line, so identical bytes written
+by package initialization or user code remain ordinary captured output.
+
+Loading and platform source selection are unchanged. Production,
+internal-test, external-test, recompiled-for-test, support, and generated-main
+nodes and actions remain unchanged. Exact dotted import identity, declared
+package names, aliases, variants, physical runtime directories, graph edges,
+initialization order, symbols, and publication names keep their existing roles.
+The product process and package initialization still run in list mode; no
+per-test child starts. Positive matching, option diagnostics and precedence,
+ordinary non-list no-match output, no-test-file results, and raw-file rejection
+are unchanged.
+
+The shared support implementation change legitimately changes its object,
+archive, and linked test-product bytes. Its exported signature and `.wwi` byte
+contract do not change. Existing content invalidation rebuilds the affected
+support/link actions; there is no test-result cache and no new graph identity.
+Running `-o` still executes the private product before guarded publication, and
+`-c`, destination safety, transaction rollback, prior-output preservation, and
+artifact modes are unchanged.
+
+Load, compile, assemble, archive, link, initialization, signal, timeout,
+interruption, child-start, publication, and cleanup failure paths retain their
+existing diagnostics and precedence. Parallel products keep independent
+processes, captures, environments, working directories, input descriptors, and
+ordered result slots. The changed runtime branch allocates and publishes no
+file, and existing cleanup remains responsible for `.new`, `.install`,
+`.wwtxn.*`, captures, process groups, and request scratch.
+
+The WW-native `list_mode_with_no_matches_emits_no_sentinel` observer proves
+both stages across concurrent combined and test-only products, package
+initialization, cold and warm persistent work, absence of list/accounting
+sentinels, positive deterministic selection, running `-o` retention, later
+direct execution, stage stdout/stderr equality, retained executable byte
+identity, and `.new` cleanup. The existing routing observer separately keeps
+ordinary non-list `[no matches]` plus accounting pinned.
+
+No persisted-byte contract changed: build workdir format remains `18`, test
+workdir format remains `19`, and semantic storage format remains `3`.
+
 ## 12. Candidate architectures and hard-gate decision
 
 Five candidates were developed as coherent systems, not as feature bins.

docs/spec.md

@@ -803,6 +803,17 @@ linker, and other build failures retain their diagnostic standard-error
 channel; build-action stdout and stderr remain separate. Parallel products own
 independent captures and are still emitted in canonical product order.
 
+List mode starts the same directory-owned product and therefore performs its
+ordinary package initialization, but it does not start any selected test child.
+The harness emits exactly one newline-terminated qualified name for each test
+selected by the command's filters, in descriptor order. If the selected set is
+empty, the harness emits no list payload, no `[no matches]` sentinel, and no
+accounting, and returns success; the coordinator still emits the ordinary
+successful package result. This does not alter non-list execution: a valid
+filter selecting no tests continues to emit `[no matches]` and the
+discovered/selected/started/completed accounting. A retained binary invoked
+directly has no coordinator package result.
+
 After those ordered results, an ordinary explicit `ww test` request that records
 an attributable setup, build, or execution failure emits exactly one standalone
 `FAIL\n` on standard output. The line is command-owned: it follows even a later

docs/test-system-v2.md

@@ -219,6 +219,16 @@ every `-j` level, and `-j 1` — the default — matches the former sequential
 run loop exactly. Measured on the 31-package `lib/...` walk:
 7.0s sequential, 2.4s at `-j 4`.
 
+List mode uses that same product process and initialization boundary but starts
+no per-test child. The shared language harness emits only selected qualified
+test names, one per line in descriptor order. A valid filter selecting no tests
+therefore produces no harness list bytes, no `[no matches]` marker, and no
+accounting while the process returns success; the coordinator continues with
+the package's normal `ok` result. Ordinary non-list zero-selection execution
+retains its `[no matches]` marker and accounting. Concurrent products keep
+independent empty or nonempty captures, and persistent work never caches a test
+result.
+
 Directory test binaries are always linked under the coordinator's temporary
 product root. `-c` independently requests a caller-visible executable copy and
 suppresses execution. `-o` independently requests a copy and still runs the