fix(res-to-affine): readiness guard must fail, not skip (#742)

Implements the owner ruling of 2026-09-07: **no environment may silently
run zero tests.**

## The fake green

`test_walker.ml:65 skip_unless_ready()` called `Alcotest.skip()` when
the tree-sitter
CLI or the generated grammar was absent.
`tools/vendor/tree-sitter-rescript/src/parser.c`
is gitignored (`.gitignore:112`), so **every fresh checkout** took that
path: all 32
walker cases skipped and alcotest printed

```
Test Successful in 0.018s. 0 test run.
```

with exit 0. The suite was green precisely when it was testing nothing.

This is not hypothetical. It is why the deletion of this suite's own
fixtures in
`f766dcb` went unnoticed for three weeks (restored in #741): in any
environment
lacking the grammar, a missing test corpus produced a pass.

## The change

Renames the guard to `require_ready()` and replaces both
`Alcotest.skip()` calls with
`Alcotest.failf` carrying the remedy (`cargo install tree-sitter-cli` /
`just install-grammar`). One file, 32 call sites renamed mechanically.

## Verified, both directions

| Grammar | Result |
|---|---|
| absent | `rc=1` — `32 failures! in 0.020s. 32 tests run.` |
| present | `rc=0` — `Test Successful in 1.257s. 32 tests run.` |

The important column is the **count**: previously the absent case
reported
`0 test run` and passed. `ci.yml:70-79` installs the CLI and builds the
grammar
before `dune runtest`, so CI lands in the passing row.

## Accepted cost

A fresh clone can no longer run the walker suite without installing the
tree-sitter
CLI and building the grammar first. That is the deliberate trade, chosen
over the
milder "fail under CI, skip locally".

## Note

`ocamlformat` is not available in my environment, so I could not
pre-check
`dune build @fmt`. If the formatting gate objects, say so and I will
correct it.

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/ci.yml

@@ -71,9 +71,11 @@ jobs:
         # Same rationale as the migration-assistant job (see below):
         # npm distribution is the fast CI install (~5 s). The walker
         # end-to-end tests in tools/res-to-affine/test/test_walker.ml
-        # auto-skip if the CLI / generated grammar aren't present, so
-        # this step is only required to *exercise* the walker — the
-        # build itself does not depend on it.
+        # now FAIL rather than skip when the CLI or the generated
+        # grammar is absent, so this step is a hard prerequisite for
+        # `dune runtest` — not an optional extra that merely widens
+        # coverage. Dropping it turns the walker suite red, which is
+        # the intended behaviour: see that file's header comment.
         run: npm install -g tree-sitter-cli@^0.25.0
       - name: Build pinned tree-sitter-rescript grammar
         run: ./editors/tree-sitter-rescript/scripts/install.sh
@@ -224,6 +226,20 @@ jobs:
           opam exec -- ocaml -version
       - name: Install dependencies
         run: opam install . --deps-only --with-test --with-doc --yes
+      - name: Set up Node.js
+        uses: actions/setup-node@v7.0.0
+        with:
+          node-version: "20"
+      - name: Install tree-sitter CLI (for res-to-affine walker tests)
+        # This job runs the WHOLE `dune runtest` sweep, which includes
+        # tools/res-to-affine/test/test_walker.ml. Those tests now fail
+        # rather than skip when the CLI or generated grammar is absent,
+        # so this job needs the same grammar prerequisites as `build`.
+        # Before the skip was removed, this job was green while running
+        # zero walker tests.
+        run: npm install -g tree-sitter-cli@^0.25.0
+      - name: Build pinned tree-sitter-rescript grammar
+        run: ./editors/tree-sitter-rescript/scripts/install.sh
       - name: Run tests with bisect_ppx instrumentation
         run: |
           opam exec -- dune runtest --force --instrument-with bisect_ppx

tools/res-to-affine/test/test_walker.ml

@@ -3,10 +3,16 @@
 
 (** End-to-end tests for the tree-sitter walker (#57 Phase 2b).
 
-    These tests shell out to the [tree-sitter] CLI; they are
-    automatically skipped when the CLI is not on PATH so a fresh
-    clone can still run [dune runtest] without bootstrapping the
-    grammar. CI installs tree-sitter and runs them as a gate.
+    These tests shell out to the [tree-sitter] CLI. They FAIL -- they do
+    not skip -- when the CLI or the generated grammar is absent.
+
+    A skip here was a fake green: [Alcotest.skip] on every case makes
+    alcotest print "Test Successful ... 0 test run" and exit 0, so the
+    suite was green precisely when it tested nothing. [src/parser.c] is
+    gitignored, so every fresh checkout hit that path. That is how the
+    deletion of this suite's own fixtures (f766dcb) went unnoticed for
+    three weeks. Owner ruling 2026-09-07: no environment may silently
+    run zero tests.
 
     To run locally: install tree-sitter (`cargo install
     tree-sitter-cli`), then `just install-grammar`, then `dune
@@ -62,23 +68,23 @@ let grammar_dir () =
 let grammar_built () =
   Sys.file_exists (Filename.concat (grammar_dir ()) "src/parser.c")
 
-let skip_unless_ready () =
-  if not (tree_sitter_available ()) then begin
-    Printf.printf
-      "  [skip] tree-sitter CLI not on PATH; install via `cargo install \
-       tree-sitter-cli`@\n";
-    Alcotest.skip ()
-  end;
-  if not (grammar_built ()) then begin
-    Printf.printf
-      "  [skip] grammar not built; run `just install-grammar`@\n";
-    Alcotest.skip ()
-  end
+(* Deliberately fails rather than skips: see the header comment. *)
+let require_ready () =
+  if not (tree_sitter_available ()) then
+    Alcotest.failf
+      "tree-sitter CLI not on PATH. These tests are a gate, not an \
+       optional extra; install it with `cargo install tree-sitter-cli`."
+  ;
+  if not (grammar_built ()) then
+    Alcotest.failf
+      "tree-sitter grammar not built (%s/src/parser.c is absent). \
+       Run `just install-grammar`."
+      (grammar_dir ())
 
 let fixture = "fixtures/sample.res"
 
 let test_walker_finds_side_effect_import () =
-  skip_unless_ready ();
+  require_ready ();
   let source = read_file fixture in
   let path = Filename.concat (Sys.getcwd ()) fixture in
   let findings =
@@ -99,7 +105,7 @@ let test_walker_only_module_toplevel () =
      fixture, which has the regex-scanner-matching shape at module
      top level — the walker should match it. The negative case lives
      in Phase 2c's expanded corpus. *)
-  skip_unless_ready ();
+  require_ready ();
   let source = read_file fixture in
   let path = Filename.concat (Sys.getcwd ()) fixture in
   let findings =
@@ -135,15 +141,15 @@ let lines_for_kind findings k =
     findings
 
 let test_walker_finds_raw_js () =
-  skip_unless_ready ();
+  require_ready ();
   let findings = scan_sample () in
   (* sample.res line 11: `let host = %raw(`globalThis.location.host`)`. *)
   Alcotest.(check (list int))
     "walker reports raw-js on line 11"
     [11] (lines_for_kind findings Scanner.Raw_js)
 
 let test_walker_finds_mutable_global () =
-  skip_unless_ready ();
+  require_ready ();
   let findings = scan_sample () in
   let got = lines_for_kind findings Scanner.Mutable_global in
   (* sample.res line 14: `let currentUser = ref(None)` — top-level
@@ -154,7 +160,7 @@ let test_walker_finds_mutable_global () =
     true (List.mem 14 got && List.mem 15 got)
 
 let test_walker_finds_untyped_exception () =
-  skip_unless_ready ();
+  require_ready ();
   let findings = scan_sample () in
   let got = lines_for_kind findings Scanner.Untyped_exception in
   (* sample.res has untyped-exception flavours at: line 19 (`try {`),
@@ -174,7 +180,7 @@ let test_walker_finds_untyped_exception () =
 let phase2c_fixture = "fixtures/phase2c.res"
 
 let test_walker_finds_inline_callback_record () =
-  skip_unless_ready ();
+  require_ready ();
   let source = read_file phase2c_fixture in
   let path = Filename.concat (Sys.getcwd ()) phase2c_fixture in
   let findings =
@@ -186,7 +192,7 @@ let test_walker_finds_inline_callback_record () =
     true (got <> [])
 
 let test_walker_finds_oversized_function () =
-  skip_unless_ready ();
+  require_ready ();
   let source = read_file phase2c_fixture in
   let path = Filename.concat (Sys.getcwd ()) phase2c_fixture in
   let findings =
@@ -224,28 +230,28 @@ let translate_phase3_blob () =
   String.concat "\n" (List.map snd (translate_phase3 ()))
 
 let test_translate_count () =
-  skip_unless_ready ();
+  require_ready ();
   (* userId, color, shape, and (slice 2) the generic box — 4. theirMap
      (qualified) and the let/switch stay skipped. *)
   Alcotest.(check int)
     "four structural type decls are translated"
     4 (List.length (translate_phase3 ()))
 
 let test_translate_generic_sum () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = translate_phase3_blob () in
   Alcotest.(check bool)
     "generic sum -> type Box[A] = | Box(A)"
     true (contains blob "type Box[A] =" && contains blob "| Box(A)")
 
 let test_translate_alias () =
-  skip_unless_ready ();
+  require_ready ();
   Alcotest.(check bool)
     "primitive alias -> capitalised TyCon + Int"
     true (contains (translate_phase3_blob ()) "type UserId = Int")
 
 let test_translate_nullary_sum () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = translate_phase3_blob () in
   let ok =
     contains blob "type Color =" && contains blob "| Red"
@@ -254,7 +260,7 @@ let test_translate_nullary_sum () =
   Alcotest.(check bool) "nullary sum -> leading-pipe variant form" true ok
 
 let test_translate_payload_sum () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = translate_phase3_blob () in
   let ok =
     contains blob "type Shape =" && contains blob "| Circle(Float)"
@@ -263,7 +269,7 @@ let test_translate_payload_sum () =
   Alcotest.(check bool) "primitive-payload sum -> mapped param types" true ok
 
 let test_translate_skips_non_structural () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = translate_phase3_blob () in
   (* the qualified Belt.Map.t and the let/switch must stay absent — the tool
      never guesses them; and no raw ReScript type-var ['a] leaks through. *)
@@ -291,14 +297,14 @@ let translate_phase3b_blob () =
   String.concat "\n" (List.map snd (translate_phase3b ()))
 
 let test_translate_b_count () =
-  skip_unless_ready ();
+  require_ready ();
   (* point, box, id translate; counter (mutable) and config (optional) skip. *)
   Alcotest.(check int)
     "three of five record/generic decls translate"
     3 (List.length (translate_phase3b ()))
 
 let test_translate_record () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = translate_phase3b_blob () in
   let ok =
     contains blob "struct Point {" && contains blob "x: Int"
@@ -307,19 +313,19 @@ let test_translate_record () =
   Alcotest.(check bool) "record -> struct with mapped field types" true ok
 
 let test_translate_generic_record () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = translate_phase3b_blob () in
   let ok = contains blob "struct Box[A] {" && contains blob "value: A" in
   Alcotest.(check bool) "generic record -> struct with type params" true ok
 
 let test_translate_generic_alias () =
-  skip_unless_ready ();
+  require_ready ();
   Alcotest.(check bool)
     "generic alias -> type Id[A] = A"
     true (contains (translate_phase3b_blob ()) "type Id[A] = A")
 
 let test_translate_b_skips () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = translate_phase3b_blob () in
   (* mutable + optional records must be skipped, never silently flattened. *)
   let leaked =
@@ -345,14 +351,14 @@ let translate_phase3c_blob () =
   String.concat "\n" (List.map snd (translate_phase3c ()))
 
 let test_translate_c_count () =
-  skip_unless_ready ();
+  require_ready ();
   (* answer, pi, greeting, enabled, disabled -> 5; now/counter/(a,b) skip. *)
   Alcotest.(check int)
     "five literal let-bindings translate to const"
     5 (List.length (translate_phase3c ()))
 
 let test_translate_const_int_float () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = translate_phase3c_blob () in
   let ok =
     contains blob "const answer: Int = 42;"
@@ -361,7 +367,7 @@ let test_translate_const_int_float () =
   Alcotest.(check bool) "int + float literal -> typed const" true ok
 
 let test_translate_const_string_bool () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = translate_phase3c_blob () in
   let ok =
     contains blob "const greeting: String = \"hi\";"
@@ -371,7 +377,7 @@ let test_translate_const_string_bool () =
   Alcotest.(check bool) "string + bool literal -> typed const" true ok
 
 let test_translate_c_skips () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = translate_phase3c_blob () in
   (* call / ref / destructuring bindings must never become a const. *)
   let leaked =
@@ -399,42 +405,42 @@ let partial1_blob () =
   String.concat "\n" (List.map snd (translate_partial1 ()))
 
 let test_partial_count () =
-  skip_unless_ready ();
+  require_ready ();
   Alcotest.(check int)
     "eleven module-top-level functions -> fn skeletons"
     11 (List.length (translate_partial1 ()))
 
 let test_partial_array () =
-  skip_unless_ready ();
+  require_ready ();
   Alcotest.(check bool) "array literal translated"
     true (contains (partial1_blob ()) "[x, x]")
 
 let test_partial_record () =
-  skip_unless_ready ();
+  require_ready ();
   (* nominal placeholder type `Rec`; field punning {x} -> x: x *)
   Alcotest.(check bool) "record literal -> Rec #{ ... }"
     true (contains (partial1_blob ()) "Rec #{ x: x, y: y }")
 
 let test_partial_pipe () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = partial1_blob () in
   (* x->doStuff(1) -> doStuff(x, 1); chain x->f->g(2) -> g(f(x), 2) *)
   Alcotest.(check bool) "pipe-first desugars, including left-nested chains"
     true (contains blob "doStuff(x, 1)" && contains blob "g(f(x), 2)")
 
 let test_partial_if () =
-  skip_unless_ready ();
+  require_ready ();
   Alcotest.(check bool) "if/else translated"
     true (contains (partial1_blob ()) "if x > 0 { x } else { 0 }")
 
 let test_partial_block () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = partial1_blob () in
   Alcotest.(check bool) "block body with a let statement translated"
     true (contains blob "let y = x + 1" && contains blob "y * 2")
 
 let test_partial_switch_to_match () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = partial1_blob () in
   let ok =
     contains blob "fn classify(x: _) -> _" && contains blob "match x {"
@@ -443,7 +449,7 @@ let test_partial_switch_to_match () =
   Alcotest.(check bool) "switch -> match with translated arms + patterns" true ok
 
 let test_partial_float_op_normalised () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = partial1_blob () in
   Alcotest.(check bool) "float op normalised; multi-param skeleton"
     true
@@ -452,14 +458,14 @@ let test_partial_float_op_normalised () =
     && not (contains blob "*."))
 
 let test_partial_concat_and_call () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = partial1_blob () in
   Alcotest.(check bool) "string concat + member-call translated"
     true
     (contains blob "\"hi \" ++ name" && contains blob "Js.log(msg)")
 
 let test_partial_todo_hole () =
-  skip_unless_ready ();
+  require_ready ();
   let blob = partial1_blob () in
   Alcotest.(check bool) "untranslatable form becomes a () /* TODO */ hole"
     true (contains blob "() /* TODO:")