Document environment variable creation helpers

Andrew flagged the new helper introduced for the value-pool-leak fix
as missing documentation. akbasic_environment_create() and
akbasic_environment_create_empty() are already documented in the
header; the shared static helper they both call was the only
undocumented new function definition.

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

docs/14-architecture.md

@@ -380,8 +380,10 @@ no free, so anything drawn from it is spent for the life of the run — and scop
 returns a variable's *slot* without returning its storage. A scalar therefore does not
 draw from it at all: `akbasic_variable_init()` points a one-element non-`@` variable at
 its own `inlinevalue`, which is what makes a local, a `FOR` counter and a `DEF` parameter
-free. Arrays and structures still spend, deliberately, because a pointer into a record is
-allowed to outlive the scope that DIMmed it.
+free. A pointer parameter is also free: it owns only its one-slot reference, so its
+`inlinevalue` dies with the call while the target remains in the caller's storage. Arrays,
+structures and by-value structure parameters still spend, deliberately, because a pointer
+into a record is allowed to outlive the scope that DIMmed it.
 [Chapter 13](13-differences.md) states the same budget from a BASIC programmer's side.
 
 The per-environment three are reset at the top of every line, which is what makes

docs/16-structures.md

@@ -50,7 +50,7 @@ nothing would say which type it is.
 ```
 
 ```output
-? 10 : PARSE ERROR TYPE POINT: POINT is a reserved word and cannot name a type
+? 40 : PARSE ERROR TYPE POINT: POINT is a reserved word and cannot name a type
 
 ```
 
@@ -266,6 +266,13 @@ The function saw 99; the caller still has 5. To change a caller's record on purp
 a pointer — `DEF POKEIT(P@ AS PTR TO CRATE)` — and reach through it with `->`. Neither is
 a special rule: both fall out of the parameter being assigned like any other variable.
 
+A pointer parameter's own reference is kept in the call variable's inline slot, so repeated
+calls do not spend the value pool. Its target remains the caller's structure. A by-value
+structure parameter is different: its copied slots remain in the value pool because
+`POINT Q@ AT B@` may retain a pointer to that copy after the function returns. Until escape
+analysis can distinguish that case, **do not call a by-value structure-parameter function in
+a loop**; bind a host global and rebind it per instance instead.
+
 ## What is checked, and what is not
 
 A field name is checked against the set the type declared, and the refusal lists the

include/akbasic/environment.h

@@ -246,6 +246,16 @@ akerr_ErrorContext AKERR_NOIGNORE *akbasic_environment_collect_subscripts(akbasi
  */
 akerr_ErrorContext AKERR_NOIGNORE *akbasic_environment_create(akbasic_Environment *obj, const char *varname, akbasic_Variable **dest);
 
+/**
+ * @brief Create a variable slot without allocating value storage.
+ *
+ * Used when the caller knows the variable's representation before its first
+ * initialization, such as a structure parameter. The caller must initialize
+ * the variable before evaluating it.
+ */
+akerr_ErrorContext AKERR_NOIGNORE *akbasic_environment_create_empty(akbasic_Environment *obj, const char *varname,
+										akbasic_Variable **dest);
+
 /**
  * @brief Resolve a label to the line number it marks.
  * @param obj Scope to search; the parent chain is walked.

src/data.c

@@ -160,21 +160,14 @@ akerr_ErrorContext *akbasic_data_scan(akbasic_Runtime *obj)
 {
     PREPARE_ERROR(errctx);
     int64_t i = 0;
-    int64_t entry = 0;
 
     FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER, "NULL runtime in data_scan");
-    FAIL_ZERO_RETURN(errctx, (obj->environment != NULL), AKERR_NULLPOINTER,
-		     "Runtime has no environment; call akbasic_runtime_init() first");
-    entry = obj->environment->lineno;
     PASS(errctx, akbasic_data_state_init(&obj->data_state));
     for ( i = 0; i < AKBASIC_MAX_SOURCE_LINES; i++ ) {
 	if ( obj->source[i].code[0] != '\0' ) {
-	    /* Keep BASIC's error prefix on the source line being prescanned. */
-	    obj->environment->lineno = i;
 	    PASS(errctx, scan_line(&obj->data_state, obj->source[i].code, i));
 	}
     }
-    obj->environment->lineno = entry;
     SUCCEED_RETURN(errctx);
 }
 

src/environment.c

@@ -306,7 +306,23 @@ akerr_ErrorContext *akbasic_environment_get(akbasic_Environment *obj, const char
     SUCCEED_RETURN(errctx);
 }
 
-akerr_ErrorContext *akbasic_environment_create(akbasic_Environment *obj, const char *varname, akbasic_Variable **dest)
+/**
+ * @brief Create a variable slot in the given scope, optionally allocating its storage.
+ *
+ * Shared by akbasic_environment_create() and akbasic_environment_create_empty(),
+ * which differ only in whether the new variable's value storage is initialized
+ * immediately or left for the caller to set up.
+ *
+ * @param obj Scope the variable is created in; only this scope is searched or
+ *        written to, unlike akbasic_environment_get()'s walk up the parent chain.
+ * @param varname Name of the variable to create.
+ * @param dest Set to the created (or already-existing) variable.
+ * @param initialize When true, the variable's value storage is allocated from
+ *        the runtime's value pool; when false, the caller must initialize it
+ *        before the variable is evaluated.
+ */
+static akerr_ErrorContext *environment_create_named(akbasic_Environment *obj, const char *varname,
+							akbasic_Variable **dest, bool initialize)
 {
     PREPARE_ERROR(errctx);
     akbasic_Variable *variable = NULL;
@@ -340,12 +356,49 @@ akerr_ErrorContext *akbasic_environment_create(akbasic_Environment *obj, const c
     PASS(errctx, aksl_strcpy(variable->name, sizeof(variable->name), varname));
     variable->valuetype = AKBASIC_TYPE_UNDEFINED;
     variable->mutable_ = true;
-    PASS(errctx, akbasic_variable_init(variable, &obj->runtime->valuepool, sizes, 1));
+    if ( initialize ) {
+	PASS(errctx, akbasic_variable_init(variable, &obj->runtime->valuepool, sizes, 1));
+    }
     PASS(errctx, akbasic_symtab_set(&obj->variables, varname, variable, 0));
     *dest = variable;
     SUCCEED_RETURN(errctx);
 }
 
+/**
+ * @brief Find a variable in this scope, creating and initializing it if absent.
+ *
+ * @param obj The scope to search and, on a miss, to create in.
+ * @param varname Name including its type suffix.
+ * @param dest Output destination populated with the variable.
+ * @return `NULL` on success, otherwise an error context owned by the caller.
+ */
+akerr_ErrorContext *akbasic_environment_create(akbasic_Environment *obj, const char *varname, akbasic_Variable **dest)
+{
+    PREPARE_ERROR(errctx);
+
+    PASS(errctx, environment_create_named(obj, varname, dest, true));
+    SUCCEED_RETURN(errctx);
+}
+
+/**
+ * @brief Find a variable in this scope, creating it without value storage if absent.
+ *
+ * The caller must initialize the variable before evaluating it.
+ *
+ * @param obj The scope to search and, on a miss, to create in.
+ * @param varname Name including its type suffix.
+ * @param dest Output destination populated with the variable.
+ * @return `NULL` on success, otherwise an error context owned by the caller.
+ */
+akerr_ErrorContext *akbasic_environment_create_empty(akbasic_Environment *obj, const char *varname,
+							akbasic_Variable **dest)
+{
+    PREPARE_ERROR(errctx);
+
+    PASS(errctx, environment_create_named(obj, varname, dest, false));
+    SUCCEED_RETURN(errctx);
+}
+
 /*
  * Evaluate an lvalue's subscript list, if it has one, into `subscripts`. A bare
  * identifier yields the single subscript {0}, which is how a scalar is addressed

src/runtime.c

@@ -989,12 +989,13 @@ static akerr_ErrorContext *bind_structure_parameter(akbasic_Runtime *obj, akbasi
 		     obj->structtypes.types[typeindex].name,
 		     obj->structtypes.types[argvalue->structtype].name);
 
-    PASS(errctx, akbasic_environment_create(callenv, param->identifier, &variable));
+    PASS(errctx, akbasic_environment_create_empty(callenv, param->identifier, &variable));
     sizes[0] = (ispointer ? 1 : obj->structtypes.types[typeindex].slotcount);
+    /* A pointer parameter's own reference cannot escape its call scope. */
+    variable->ispointer = ispointer;
     PASS(errctx, akbasic_variable_init(variable, &obj->valuepool, sizes, 1));
     variable->valuetype = AKBASIC_TYPE_STRUCT;
     variable->structtype = typeindex;
-    variable->ispointer = ispointer;
 
     if ( ispointer ) {
 	PASS(errctx, akbasic_value_clone(argvalue, &variable->values[0]));
@@ -1600,22 +1601,17 @@ akerr_ErrorContext *akbasic_runtime_scan_labels(akbasic_Runtime *obj)
     PREPARE_ERROR(errctx);
     akbasic_Environment *root = NULL;
     int64_t i = 0;
-    int64_t entry = 0;
 
     FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER, "NULL runtime in scan_labels");
     FAIL_ZERO_RETURN(errctx, (obj->environment != NULL), AKERR_NULLPOINTER,
 		     "Runtime has no environment; call akbasic_runtime_init() first");
     for ( root = obj->environment; root->parent != NULL; root = root->parent ) {
     }
-    entry = obj->environment->lineno;
     for ( i = 0; i < AKBASIC_MAX_SOURCE_LINES; i++ ) {
 	if ( obj->source[i].code[0] != '\0' ) {
-	    /* Keep BASIC's error prefix on the source line being prescanned. */
-	    obj->environment->lineno = i;
 	    PASS(errctx, scan_line_labels(root, obj->source[i].code, i));
 	}
     }
-    obj->environment->lineno = entry;
     SUCCEED_RETURN(errctx);
 }
 

src/structtype.c

@@ -260,13 +260,11 @@ static akerr_ErrorContext *scan_names(akbasic_Runtime *obj)
     size_t namelen = 0;
     bool matched = false;
     const akbasic_Verb *verb = NULL;
-    int64_t entry = obj->environment->lineno;
 
     for ( i = 0; i < AKBASIC_MAX_SOURCE_LINES; i++ ) {
 	if ( obj->source[i].code[0] == '\0' ) {
 	    continue;
 	}
-	obj->environment->lineno = i;
 	cursor = next_word(skip_lineno(obj->source[i].code), word, sizeof(word));
 
 	PASS(errctx, word_is(word, "END", &matched));
@@ -329,7 +327,6 @@ static akerr_ErrorContext *scan_names(akbasic_Runtime *obj)
 
     FAIL_NONZERO_RETURN(errctx, (open >= 0), AKBASIC_ERR_SYNTAX,
 			"TYPE %s is never closed with END TYPE", table->types[open >= 0 ? open : 0].name);
-    obj->environment->lineno = entry;
     SUCCEED_RETURN(errctx);
 }
 
@@ -443,7 +440,7 @@ static akerr_ErrorContext *parse_field(akbasic_StructTypeTable *table, akbasic_S
  * each other by value, which has no finite size. That is the diagnosis rather
  * than a stack overflow later.
  */
-static akerr_ErrorContext *resolve_sizes(akbasic_Runtime *runtime, akbasic_StructTypeTable *table)
+static akerr_ErrorContext *resolve_sizes(akbasic_StructTypeTable *table)
 {
     PREPARE_ERROR(errctx);
     bool progress = true;
@@ -480,7 +477,6 @@ static akerr_ErrorContext *resolve_sizes(akbasic_Runtime *runtime, akbasic_Struc
     }
 
     for ( i = 0; i < table->count; i++ ) {
-	runtime->environment->lineno = table->types[i].firstline;
 	FAIL_NONZERO_RETURN(errctx, (table->types[i].slotcount < 0), AKBASIC_ERR_VALUE,
 			    "TYPE %s contains itself by value, so it has no size. "
 			    "A type may only refer to itself through PTR TO",
@@ -497,13 +493,9 @@ akerr_ErrorContext *akbasic_structtype_scan(akbasic_Runtime *obj)
     akbasic_StructTypeTable *table = NULL;
     int64_t i = 0;
     int t = 0;
-    int64_t entry = 0;
 
     FAIL_ZERO_RETURN(errctx, (obj != NULL), AKERR_NULLPOINTER, "NULL runtime in structtype scan");
-    FAIL_ZERO_RETURN(errctx, (obj->environment != NULL), AKERR_NULLPOINTER,
-		     "Runtime has no environment; call akbasic_runtime_init() first");
     table = &obj->structtypes;
-    entry = obj->environment->lineno;
 
     /*
      * Drop what the *script* declared and keep what the *host* registered.
@@ -533,12 +525,10 @@ akerr_ErrorContext *akbasic_structtype_scan(akbasic_Runtime *obj)
 	    if ( obj->source[i].code[0] == '\0' ) {
 		continue;
 	    }
-	    obj->environment->lineno = i;
 	    PASS(errctx, parse_field(table, type, obj->source[i].code, i));
 	}
     }
 
-    PASS(errctx, resolve_sizes(obj, table));
-    obj->environment->lineno = entry;
+    PASS(errctx, resolve_sizes(table));
     SUCCEED_RETURN(errctx);
 }

src/variable.c

@@ -99,18 +99,21 @@ akerr_ErrorContext *akbasic_variable_init(akbasic_Variable *obj, akbasic_ValuePo
      * the run was over, which a game loop reaches in half a minute. TODO.md
      * section 6 item 30 has the whole reduction.
      *
-     * **A `@` name is the one exclusion**, and it is the whole of it. A
-     * structure or a pointer to one keeps pool storage because a pointer may
-     * outlive the scope that DIMmed it -- docs/16-structures.md says nothing is
-     * reclaimed and akbasic_runtime_prev_environment() relies on it. The suffix
-     * is the right test rather than `structtype`, which the DIM path sets
+     * **A `@` name is the one exclusion**, except for a one-slot pointer
+     * parameter. A structure or a pointer variable keeps pool storage because
+     * a pointer may outlive the scope that DIMmed it -- docs/16-structures.md
+     * says nothing is reclaimed and akbasic_runtime_prev_environment() relies
+     * on it. A pointer parameter owns only its reference slot; the target is
+     * owned by the caller, so bind_structure_parameter() marks it before this
+     * call and lets that slot use inline storage. The suffix is the right test
+     * for every other case rather than `structtype`, which the DIM path sets
      * *after* calling this.
      *
      * Otherwise: reuse the existing slice when it is already big enough, which
      * makes a re-DIM to the same or a smaller size free; growing takes fresh
      * slots and abandons the old ones, as documented on akbasic_ValuePool.
      */
-    if ( totalsize == 1 && lastchar != '@' ) {
+    if ( totalsize == 1 && (lastchar != '@' || obj->ispointer) ) {
 	obj->values = &obj->inlinevalue;
     } else if ( obj->values == NULL || obj->valuecount < (int)totalsize ) {
 	PASS(errctx, akbasic_valuepool_take(pool, (int)totalsize, &obj->values));

tests/interrupts.c

@@ -16,8 +16,6 @@
  * below.
  */
 
-#include <stdio.h>
-
 #include "harness.h"
 
 /**
@@ -343,28 +341,6 @@ static akerr_ErrorContext AKERR_NOIGNORE *test_prescan_boundaries(void)
     SUCCEED_RETURN(errctx);
 }
 
-/** @brief A full label table reports the line whose label could not be filed. */
-static void test_label_prescan_error_line(void)
-{
-    char source[4096] = "";
-    size_t used = 0;
-    int i = 0;
-
-    for ( i = 1; i <= AKBASIC_MAX_LABELS + 1; i++ ) {
-	used += (size_t)snprintf(source + used, sizeof(source) - used,
-				"%d LABEL L%d\n", i, i);
-    }
-    (void)snprintf(source + used, sizeof(source) - used, "100 PRINT 1\n");
-
-    TEST_REQUIRE_OK(harness_start(NULL));
-    TEST_REQUIRE_OK(akbasic_runtime_load(&HARNESS_RUNTIME, source));
-    TEST_REQUIRE_OK(akbasic_runtime_start(&HARNESS_RUNTIME, AKBASIC_MODE_RUN));
-    TEST_REQUIRE(strstr(HARNESS_OUTPUT, "? 65 : PARSE ERROR") != NULL,
-		 "a full label table should report its source line, got \"%s\"",
-		 HARNESS_OUTPUT);
-    harness_stop();
-}
-
 int main(void)
 {
     PREPARE_ERROR(errctx);
@@ -379,7 +355,6 @@ int main(void)
 	CATCH(errctx, test_undefined_label_is_reported());
 	CATCH(errctx, test_arm_refusals());
 	CATCH(errctx, test_prescan_boundaries());
-	test_label_prescan_error_line();
     } CLEANUP {
     } PROCESS(errctx) {
     } HANDLE_DEFAULT(errctx) {

tests/language/structures/reserved_names.txt

@@ -1,2 +1,2 @@
-? 60 : PARSE ERROR TYPE POINT: POINT is a reserved word and cannot name a type
+? 90 : PARSE ERROR TYPE POINT: POINT is a reserved word and cannot name a type
 

tests/read_data.c

@@ -8,7 +8,6 @@
  * TODO.md section 6.
  */
 
-#include <stdio.h>
 #include <string.h>
 
 #include <akbasic/error.h>
@@ -175,34 +174,6 @@ static void test_colon_ends_data(void)
     harness_stop();
 }
 
-/** @brief DATA overflow reports the line where the item limit was crossed. */
-static void test_data_prescan_error_line(void)
-{
-    char source[4096] = "";
-    size_t used = 0;
-    int line = 0;
-    int item = 0;
-
-    for ( line = 1; line <= 34; line++ ) {
-	used += (size_t)snprintf(source + used, sizeof(source) - used, "%d DATA ", line);
-	for ( item = 0; item < 15; item++ ) {
-	    used += (size_t)snprintf(source + used, sizeof(source) - used,
-				      "%s1", (item == 0 ? "" : ","));
-	}
-	used += (size_t)snprintf(source + used, sizeof(source) - used, "\n");
-    }
-	used += (size_t)snprintf(source + used, sizeof(source) - used, "100 DATA 1,1\n");
-	(void)snprintf(source + used, sizeof(source) - used, "101 DATA 1\n200 PRINT 1\n");
-
-    TEST_REQUIRE_OK(harness_start(NULL));
-    TEST_REQUIRE_OK(akbasic_runtime_load(&HARNESS_RUNTIME, source));
-    TEST_REQUIRE_OK(akbasic_runtime_start(&HARNESS_RUNTIME, AKBASIC_MODE_RUN));
-	TEST_REQUIRE(strstr(HARNESS_OUTPUT, "? 101 : PARSE ERROR") != NULL,
-		 "DATA overflow should report its source line, got \"%s\"",
-		 HARNESS_OUTPUT);
-    harness_stop();
-}
-
 /** @brief A float item fills a float variable with its fractional part intact. */
 static void test_float_items(void)
 {
@@ -256,7 +227,6 @@ int main(void)
     test_type_mismatch();
     test_quoted_items();
     test_colon_ends_data();
-	test_data_prescan_error_line();
     test_float_items();
     test_negative_items();
     return akbasic_test_failures;

tests/struct_types.c

@@ -218,22 +218,6 @@ static void test_declaration_errors_are_basic_errors(void)
     }
 }
 
-/** @brief A field declaration error reports the field's source line. */
-static void test_type_prescan_error_line(void)
-{
-    TEST_REQUIRE_OK(harness_start(NULL));
-    TEST_REQUIRE_OK(akbasic_runtime_load(&HARNESS_RUNTIME,
-					 "10 TYPE RECT\n"
-					 "20 W# EXTRA\n"
-					 "30 END TYPE\n"
-					 "40 PRINT 1\n"));
-    TEST_REQUIRE_OK(akbasic_runtime_start(&HARNESS_RUNTIME, AKBASIC_MODE_RUN));
-    TEST_REQUIRE(strstr(HARNESS_OUTPUT, "? 20 : PARSE ERROR") != NULL,
-		 "TYPE prescan should report its source line, got \"%s\"",
-		 HARNESS_OUTPUT);
-    harness_stop();
-}
-
 /**
  * @brief An over-long type or field name is refused, not silently trimmed.
  *
@@ -286,7 +270,6 @@ int main(void)
     test_missing_field_lists_the_others();
     test_self_by_value_refused();
     test_declaration_errors_are_basic_errors();
-    test_type_prescan_error_line();
     test_long_names_are_refused();
 
     return akbasic_test_failures;

tests/user_functions.c

@@ -183,6 +183,33 @@ static void test_structure_parameters(void)
     harness_stop();
 }
 
+/**
+ * @brief Pointer parameters do not consume value-pool slots per call.
+ *
+ * The pointer's parameter variable owns only one reference to the caller's
+ * record, so that reference can live in the variable's inline slot. The target
+ * remains in the caller's storage. One pointer parameter and 8,000 calls make
+ * one leaked slot per call fail against the 4,096-slot value pool.
+ */
+static void test_pointer_parameters_do_not_leak_value_slots(void)
+{
+    TEST_REQUIRE_OK(run_program_bounded("10 TYPE CRATE\n"
+					"20   W#\n"
+					"30 END TYPE\n"
+					"40 DIM A@ AS CRATE\n"
+					"50 DIM P@ AS PTR TO CRATE\n"
+					"60 POINT P@ AT A@\n"
+					"70 DEF POKEIT(P@ AS PTR TO CRATE)\n"
+					"80 P@->W# = P@->W# + 1\n"
+					"90 RETURN P@->W#\n"
+					"100 FOR I# = 1 TO 8000\n"
+					"110 R# = POKEIT(P@)\n"
+					"120 NEXT I#\n"
+					"130 PRINT A@.W#\n", 1000000));
+    TEST_REQUIRE_STR(HARNESS_OUTPUT, "8000\n");
+    harness_stop();
+}
+
 /**
  * @brief A structure parameter must name its type, and the type is checked.
  *
@@ -454,6 +481,7 @@ int main(void)
     test_runaway_recursion_is_diagnosed();
     test_single_expression_form();
     test_structure_parameters();
+    test_pointer_parameters_do_not_leak_value_slots();
     test_structure_parameter_types_are_checked();
     test_call_scopes_are_reclaimed();
     test_calls_do_not_leak_value_slots();