Move BASIC fixtures into the editable language corpus

Move every program and expectation out of tests/reference and register the unified tests/language corpus as local cases. Remove the old immutable-corpus protections from build, maintenance, and documentation paths.

Co-authored-by: andrew <andrew@aklabs.net>

tests/for_semantics.c

@@ -81,7 +81,7 @@ static void test_counter_survives_the_loop(void)
  * `FOR I = 1 TO 1` executes the body one time on every BASIC there has ever
  * been. Here the entry test treats "the counter has reached the limit" as
  * "do not enter", so the body is skipped entirely -- and
- * tests/reference/language/flowcontrol/forloopwaitingforcommand.bas pins that,
+ * tests/language/flowcontrol/forloopwaitingforcommand.bas pins that,
  * which is why this cannot simply be corrected.
  */
 static void test_single_iteration_loop(void)

tests/language/README.md

@@ -0,0 +1,16 @@
+# The language test corpus
+
+The `.bas` files in this directory and their sibling `.txt` files are the editable language
+corpus. CMake registers every program as an individual `local_*` CTest case and compares its
+output with the sibling expectation.
+
+The corpus includes cases carried over from the deprecated Go implementation as well as cases
+written for this interpreter. Their provenance is useful when investigating a regression, but it
+does not make any case immutable or turn the old implementation into a specification.
+
+**Change a program and its expectation deliberately and in the same commit.** If the changed
+output represents an intentional language decision, record the reason in `TODO.md` or the
+relevant documentation. If it is an accidental change, fix the interpreter instead.
+
+The `examples/` subdirectory contains complete BASIC programs used as worked examples. It is
+part of the same corpus and follows the same `.bas`/`.txt` pairing rule.

tests/reference/README.md

@@ -1,63 +0,0 @@
-# The reference interpreter's own test corpus
-
-These 41 `.bas` files and their 41 `.txt` expectations are **not this project's tests.** They
-are a byte-for-byte copy of the acceptance corpus belonging to the Go implementation this
-interpreter was ported from:
-
-| | |
-|---|---|
-| Source | `https://source.starfort.tech/andrew/basicinterpreter`, `tests/` |
-| Copied at | commit `d76162cb37eeaccddae2cf6cab7af7bc8175d6d2` ("Update README.md") |
-| Copied on | 2026-07-31 |
-| Verified | every file `cmp`-identical to the submodule at the time of the copy |
-
-They are registered as the `golden_*` CTest cases and run against `basic` on every build, in
-both the default and the `-DAKBASIC_WITH_AKGL=ON` configurations.
-
-## Why they are a copy, when they deliberately were not
-
-Until 2026-07-31 these were driven *in place* out of `deps/basicinterpret`, and the reasoning
-was written down in `CMakeLists.txt`: the corpus is a submodule, and copying a submodule's
-corpus guarantees drift.
-
-That reasoning was sound and it stopped applying. The Go project is deprecated and will not be
-updated, so there is nothing left to drift *from* — and a build that cannot run its own
-acceptance suite without cloning the implementation it replaced is not finished.
-
-## What these are for now
-
-**A regression suite, not a specification.** That distinction is the whole of how to treat
-them, and it changed on 2026-07-31 (`TODO.md` §0.1): matching the Go implementation is no
-longer a goal, so a difference between it and this interpreter is not automatically a bug in
-this one.
-
-What they are still good for is unchanged and is worth a lot: forty-one real BASIC programs
-with known-good output, covering arithmetic, arrays, flow control, every builtin function,
-`READ`/`DATA`, labels and three worked examples. That catches regressions whatever its
-provenance.
-
-## The rule for editing these
-
-**Diverge deliberately, never by accident.**
-
-A failure here means this interpreter's behaviour changed. Nine times in ten that is a bug you
-just introduced and the answer is to fix the code. The tenth time it is an improvement on the
-reference, and then the answer is:
-
-1. Change the expectation in the same commit as the code.
-2. Say why in the commit message.
-3. Add a line to `TODO.md` §5, which is the list of deliberate deviations.
-
-What is not acceptable is editing a `.txt` to make a red suite green without deciding which of
-the two you are doing.
-
-New cases for this project's own behaviour go in `tests/language/`, registered under `local_*`.
-The prefix says which corpus a failure came from, and a diff touching `tests/reference/` stands
-out as the thing it is.
-
-## Divergences so far
-
-| Case | Change | Why |
-|---|---|---|
-| `language/arithmetic/integer.txt` | Expectation grew from `4 4 2` to `4 4 2 2` | The program has **four** `PRINT` statements and the expectation had three values. The file ends in a blank line, and both interpreters filed a blank line under the loader's cursor — which for a line with no number of its own is the number of the line before it. So `40 PRINT 4 - 2` was erased before the program ran. The reference lost it the same way, which is why the expectation was written short. Fixed by skipping blank lines in RUNSTREAM, as `akbasic_runtime_load()` and `DLOAD` already did. `TODO.md` §5. |
-| `examples/strreverse.bas` | Variable `INPUT$` renamed to `SOURCE$` | `INPUT$` is a reserved word with a type suffix, which a real C128 refuses and which this interpreter now refuses too (`TODO.md` §6 item 16). The reference accepted it only because its own reserved-word check never fired. The expectation is byte-for-byte unchanged — the program still prints `REVERSED: OLLEH` — so the case keeps all of its value. |

tests/structure_verbs.c

@@ -358,7 +358,7 @@ static void test_skipped_block_releases_its_loop_scope(void)
  * inner `NEXT`, so the outer `NEXT` still finds its own `FOR`. Releasing it
  * turns this into "NEXT outside the context of FOR".
  *
- * tests/reference/language/flowcontrol/nestedforloopwaitingforcommand.bas is the
+ * tests/language/flowcontrol/nestedforloopwaitingforcommand.bas is the
  * golden case that caught exactly that, and this is the same shape asserted
  * where a reader of this file will see it.
  */

tests/unnumbered.c

@@ -182,7 +182,7 @@ static void test_runstream_assigns_the_same_slots(void)
 /**
  * @brief A file ending in a blank line keeps its last line.
  *
- * `tests/reference/language/arithmetic/integer.bas` is this shape, and both this
+ * `tests/language/arithmetic/integer.bas` is this shape, and both this
  * interpreter and the reference used to erase the last line before running it --
  * the blank line was filed under the cursor, which for a line with no number of
  * its own is the number of the line before it.