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Forward WINDOW through the tee sink

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`akbasic_sink_init_tee()` wired write, writeln, readline, clear and --
conditionally -- moveto, and never `window`. The standalone AKGL frontend runs
the interpreter against a tee, so the fully implemented `sink_window()`
underneath it was unreachable: `WINDOW 0, 0, 20, 4` answered "WINDOW needs a
text device with a character grid, and this one has none" on the one build that
has a character grid. It reads as an oversight rather than a decision, because
`moveto` directly above it is forwarded with reasoning that applies unchanged.

`tee_window()` is that function, modelled on `tee_moveto()`, offered only when a
half can take it so the refusal still reads correctly through a stdio-only pair.

**Writing the test found a second one.** Both optional entry points are assigned
conditionally, and neither initializer cleared them first -- so a caller with a
sink on the stack got whatever was in that memory, and `CHAR` and `WINDOW`
decide whether they can act by testing those pointers for NULL. Both
`akbasic_sink_init_tee()` and `akbasic_sink_init_stdio()` now clear them. An
initializer that leaves a field alone is not an initializer.

tests/sink_tee.c gains a stand-in sink with a grid -- the two stdio halves have
neither entry point, which is exactly why they could not show that either is
forwarded -- and asserts both directions, the arguments arriving intact, and
that a grid-less pair still offers neither.

Verified end to end: `WINDOW 0, 0, 20, 4` then `PRINT` succeeds under
build-akgl/basic and still refuses by name under build/basic.

What this does *not* fix is that a drawing still has to be re-issued every
frame: the frontend never clears and SDL is double-buffered, so a drawing issued
once appears in one buffer only. Shrinking the text area makes the rest of the
window the program's; keeping something there is still the program's job. That
half is documented rather than fixed, and is filed as TODO.md section 9 item 5.

TODO.md section 6 item 31, struck.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Andrew Kesterson
2026-08-01 23:57:57 -04:00
parent 5d33237eed
commit fd1f0d7c19
4 changed files with 142 additions and 1 deletions
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15
TODO.md
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@@ -1932,7 +1932,20 @@ in either corpus runs for minutes, which is why the first of these had never bee
has to be settled with it: while the pool is dry the failure cannot be trapped, so a
program cannot even report this one against itself.
31. **`WINDOW` cannot be reached in the standalone AKGL build.** `akbasic_sink_init_tee()`
31. ~~**`WINDOW` cannot be reached in the standalone AKGL build.**~~ **Done** — `tee_window()`
(`src/sink_tee.c`) forwards to whichever half offers one, offered only when one does,
with the case in `tests/sink_tee.c` beside the `moveto` one. `WINDOW 0, 0, 20, 4` now
works in the windowed build and still refuses by name without a grid.
**`akbasic_sink_init_tee()` and `akbasic_sink_init_stdio()` also now clear `moveto` and
`window` rather than leaving them alone.** Writing the test found it: both are
conditional in the tee, so a caller with a sink on the stack got whatever was in that
memory, and `CHAR` decides whether it can move a cursor by testing that pointer for
NULL. An initializer that leaves a field alone is not an initializer.
The grid-size half of this item is closed separately; see item 31a below.
The original report: `akbasic_sink_init_tee()`
(`src/sink_tee.c:143`) wires `write`, `writeln`, `readline`, `clear` and -- conditionally
-- `moveto`, and never sets `window`. The standalone frontend runs the interpreter against
the tee (`src/frontend_akgl.c:215`), so the fully implemented `sink_window()` underneath it

8
src/sink_stdio.c
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@@ -100,5 +100,13 @@ akerr_ErrorContext *akbasic_sink_init_stdio(akbasic_TextSink *obj, akbasic_Stdio
obj->writeln = stdio_writeln;
obj->readline = stdio_readline;
obj->clear = stdio_clear;
/*
* The optional entry points, cleared rather than left alone. A stream has no
* character grid, so `CHAR` and `WINDOW` must refuse by name -- and they
* decide that by testing the pointer for NULL. A caller with a sink on the
* stack would otherwise hand them whatever was in that memory.
*/
obj->moveto = NULL;
obj->window = NULL;
SUCCEED_RETURN(errctx);
}

42
src/sink_tee.c
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@@ -115,6 +115,34 @@ static akerr_ErrorContext *tee_moveto(akbasic_TextSink *self, int col, int row)
SUCCEED_RETURN(errctx);
}
/**
* @brief Constrain whichever half has a grid, for WINDOW.
*
* Same shape as tee_moveto() above it, and for the same reason: a stdio half has
* no grid to constrain and a windowed half does, so the call goes to whoever can
* take it and the other is left alone.
*
* This was missing, and its absence made `WINDOW` unreachable in the one build
* that has a character grid -- the standalone AKGL frontend runs the interpreter
* against a tee, so the fully implemented sink_window() underneath answered
* nothing. `WINDOW` refused with "needs a text device with a character grid" on
* the build that had one. TODO.md section 6 item 31.
*/
static akerr_ErrorContext *tee_window(akbasic_TextSink *self, int left, int top, int right, int bottom)
{
PREPARE_ERROR(errctx);
akbasic_TeeSink *state = NULL;
PASS(errctx, tee_state(self, &state));
if ( state->primary != NULL && state->primary->window != NULL ) {
PASS(errctx, state->primary->window(state->primary, left, top, right, bottom));
}
if ( state->mirror != NULL && state->mirror->window != NULL ) {
PASS(errctx, state->mirror->window(state->mirror, left, top, right, bottom));
}
SUCCEED_RETURN(errctx);
}
akerr_ErrorContext *akbasic_sink_init_tee(akbasic_TextSink *obj, akbasic_TeeSink *state, akbasic_TextSink *primary, akbasic_TextSink *mirror, akbasic_TextSink *reader)
{
PREPARE_ERROR(errctx);
@@ -141,6 +169,14 @@ akerr_ErrorContext *akbasic_sink_init_tee(akbasic_TextSink *obj, akbasic_TeeSink
obj->writeln = tee_writeln;
obj->readline = tee_readline;
obj->clear = tee_clear;
/*
* Cleared first, because the two below are conditional and an initializer
* that leaves a field alone is not an initializer: a caller with a sink on
* the stack would get whatever was in that memory, and `CHAR` decides
* whether it can move a cursor by testing this pointer for NULL.
*/
obj->moveto = NULL;
obj->window = NULL;
/*
* Offered only when a half can actually do it, so CHAR's refusal against a
* stdio-only driver still reads correctly through a tee.
@@ -149,5 +185,11 @@ akerr_ErrorContext *akbasic_sink_init_tee(akbasic_TextSink *obj, akbasic_TeeSink
(mirror != NULL && mirror->moveto != NULL) ) {
obj->moveto = tee_moveto;
}
/* Same rule for WINDOW, so its refusal against a grid-less pair still reads
correctly through a tee. */
if ( (primary != NULL && primary->window != NULL) ||
(mirror != NULL && mirror->window != NULL) ) {
obj->window = tee_window;
}
SUCCEED_RETURN(errctx);
}

78
tests/sink_tee.c
View File

@@ -38,6 +38,38 @@ static akerr_ErrorContext AKERR_NOIGNORE *broken_clear(akbasic_TextSink *self)
FAIL_RETURN(errctx, AKERR_IO, "this sink always fails");
}
/*
* A half that has a character grid. The two stdio sinks above have neither
* `moveto` nor `window`, which is exactly why they cannot show that either one
* is forwarded -- so this stands in for the akgl sink, without the SDL this file
* deliberately does not link.
*/
static int MOVETOS = 0;
static int WINDOWS = 0;
static int WINDOW_ARGS[4] = { 0, 0, 0, 0 };
static akerr_ErrorContext AKERR_NOIGNORE *counting_moveto(akbasic_TextSink *self, int col, int row)
{
PREPARE_ERROR(errctx);
(void)self; (void)col; (void)row;
MOVETOS += 1;
SUCCEED_RETURN(errctx);
}
static akerr_ErrorContext AKERR_NOIGNORE *counting_window(akbasic_TextSink *self, int left, int top, int right, int bottom)
{
PREPARE_ERROR(errctx);
(void)self;
WINDOWS += 1;
WINDOW_ARGS[0] = left;
WINDOW_ARGS[1] = top;
WINDOW_ARGS[2] = right;
WINDOW_ARGS[3] = bottom;
SUCCEED_RETURN(errctx);
}
int main(void)
{
akbasic_TextSink primary;
@@ -45,6 +77,7 @@ int main(void)
akbasic_TextSink mirror;
akbasic_StdioSink mirrorstate;
akbasic_TextSink broken;
akbasic_TextSink gridded;
akbasic_TextSink tee;
akbasic_TeeSink teestate;
FILE *primaryout = NULL;
@@ -106,6 +139,51 @@ int main(void)
TEST_REQUIRE_STR(line, "");
TEST_REQUIRE_STATUS(tee.readline(&tee, NULL, sizeof(line), &eof), AKERR_NULLPOINTER);
/*
* `moveto` and `window` are offered only when a half can do them, so that a
* `CHAR` or a `WINDOW` against a stdio-only pair still refuses by name
* rather than appearing to work. Two stdio halves have neither.
*/
TEST_REQUIRE_OK(akbasic_sink_init_tee(&tee, &teestate, &primary, &mirror, NULL));
TEST_REQUIRE(tee.moveto == NULL, "a tee over two grid-less sinks must not offer moveto");
TEST_REQUIRE(tee.window == NULL, "a tee over two grid-less sinks must not offer window");
/*
* And when a half *does* have them, they are forwarded. `window` used to be
* the one entry point this function never wired, which made WINDOW
* unreachable in the only build that has a character grid: the standalone
* frontend runs the interpreter against a tee, so the akgl sink's fully
* implemented window() answered nothing and the verb refused with "needs a
* text device with a character grid". TODO.md section 6 item 31.
*/
gridded.self = &gridded;
gridded.write = broken_write;
gridded.writeln = broken_write;
gridded.readline = NULL;
gridded.clear = broken_clear;
gridded.moveto = counting_moveto;
gridded.window = counting_window;
MOVETOS = 0;
WINDOWS = 0;
TEST_REQUIRE_OK(akbasic_sink_init_tee(&tee, &teestate, &primary, &gridded, NULL));
TEST_REQUIRE(tee.moveto != NULL, "a tee with a gridded half must offer moveto");
TEST_REQUIRE(tee.window != NULL, "a tee with a gridded half must offer window");
TEST_REQUIRE_OK(tee.moveto(&tee, 3, 4));
TEST_REQUIRE_OK(tee.window(&tee, 0, 20, 39, 24));
TEST_REQUIRE_INT(MOVETOS, 1);
TEST_REQUIRE_INT(WINDOWS, 1);
TEST_REQUIRE_INT(WINDOW_ARGS[0], 0);
TEST_REQUIRE_INT(WINDOW_ARGS[1], 20);
TEST_REQUIRE_INT(WINDOW_ARGS[2], 39);
TEST_REQUIRE_INT(WINDOW_ARGS[3], 24);
/* The gridded half being first is wired the same way round. */
WINDOWS = 0;
TEST_REQUIRE_OK(akbasic_sink_init_tee(&tee, &teestate, &gridded, &primary, NULL));
TEST_REQUIRE(tee.window != NULL, "the gridded half may be either one");
TEST_REQUIRE_OK(tee.window(&tee, 1, 2, 3, 4));
TEST_REQUIRE_INT(WINDOWS, 1);
/*
* A failing half stops the pair rather than being swallowed. A half-written
* line is worse than a refused one: the golden corpus compares whole files.