Reclaim BASIC strings on restart

src/bassy.nim

@@ -272,6 +272,7 @@ type
     program: Program
     strings: TextStorage
     stringLiterals: seq[int32]
+    stringRoots: seq[Value]
     limits: Limits
     globals: seq[Value]
     memory: seq[Value]
@@ -3188,7 +3189,9 @@ proc initRuntimeState(
     allocatedBytes += cells * LogicalValueBytes
   if program.usesStrings:
     allocatedBytes += storageBytes(limits.maxStrings, limits.maxStringBytes) +
-      int64(program.literals.len) * 4
+      int64(program.literals.len) * 4 +
+      (globalCells + arrayCells + hostDataCells +
+        int64(program.literals.len)) * LogicalValueBytes
   if allocatedBytes > limits.maxMemoryBytes:
     fail("BASIC runtime exceeds the configured memory limit")
   for cells in [
@@ -3233,6 +3236,11 @@ proc initRuntimeState(
     result.strings = initTextStorage(
       limits.maxStrings, limits.maxStringBytes, limits.maxStringLength
     )
+    result.stringRoots = newSeq[Value](portableCells(
+      globalCells + arrayCells + hostDataCells +
+        int64(program.literals.len),
+      "too many BASIC string roots for this target"
+    ))
     result.stringLiterals = newSeq[int32](program.literals.len)
     for handle in result.stringLiterals.mitems:
       handle = -1
@@ -3301,7 +3309,35 @@ proc reset*(runtime: var Runtime) =
   runtime.finished = false
 
 proc restart*(runtime: var Runtime) =
-  ## Restarts execution and budgets while preserving globals and arrays.
+  ## Restarts execution and reclaims strings, preserving globals and arrays.
+  ## Host-held string Values must be fetched again after restarting.
+  if runtime.program.usesStrings:
+    let
+      globals = runtime.globals.len
+      cells = runtime.memory.len
+      literals = globals + cells + runtime.hostData.len
+    for i, value in runtime.globals:
+      runtime.stringRoots[i] = value
+    for i, value in runtime.memory:
+      runtime.stringRoots[globals + i] = value
+    for i, value in runtime.hostData:
+      runtime.stringRoots[globals + cells + i] = value
+    for i, handle in runtime.stringLiterals:
+      runtime.stringRoots[literals + i] =
+        if handle >= 0:
+          stringValue(runtime.strings.empty.stringOwner, handle)
+        else:
+          Value()
+    runtime.strings.reset(runtime.stringRoots)
+    for i in 0 ..< globals:
+      runtime.globals[i] = runtime.stringRoots[i]
+    for i in 0 ..< cells:
+      runtime.memory[i] = runtime.stringRoots[globals + i]
+    for i in 0 ..< runtime.hostData.len:
+      runtime.hostData[i] = runtime.stringRoots[globals + cells + i]
+    for i, handle in runtime.stringLiterals.mpairs:
+      let value = runtime.stringRoots[literals + i]
+      handle = if value.kind == StringValue: value.stringHandle else: -1
   runtime.registers.clear
   runtime.arguments.clear
   runtime.pc = runtime.program.routines[0].entry
@@ -3527,6 +3563,13 @@ proc getString*(runtime: Runtime, value: Value): string =
   ## Reads owned text without exposing raw arena handles.
   runtime.strings.get(value)
 
+template withString*(runtime: Runtime, value: Value, text, body: untyped) =
+  ## Borrows string bytes for a block that must not modify or restart the VM.
+  block:
+    let source = runtime
+    source.strings.withText(value, text):
+      body
+
 proc putString*(runtime: var Runtime, value: string): Value =
   ## Copies host text into bounded storage for a string-valued callback.
   runtime.strings.put(value)

src/bassy/texts.nim

@@ -114,6 +114,20 @@ proc get*(storage: TextStorage, value: Value): string =
   if view.length > 0:
     result = storage.arena[int(view.start) ..< int(view.start + view.length)]
 
+template withText*(
+  storage: var TextStorage, value: Value, text, body: untyped
+) =
+  ## Borrows validated bytes until the storage is next modified.
+  block:
+    let
+      source = addr storage
+      view = source[].span(value)
+    template text: untyped =
+      source[].arena.toOpenArray(
+        int(view.start), int(view.start + view.length) - 1
+      )
+    body
+
 proc count*(storage: TextStorage): int {.raises: [].} =
   ## Returns the number of occupied string slots including the empty string.
   storage.spans.len

tests/test_strings.nim

@@ -187,7 +187,8 @@ saved$(1) = answer$
   doAssert runtime.getStringGlobal("message$") == "host global"
   runtime.setData("mail$", "new mail")
   runtime.restart
-  doAssert runtime.getString(value) == "ok"
+  doAssert runtime.getStringGlobal("answer$") == "ok"
+  doAssert errorContains(proc() = discard runtime.getString(value), "stale")
   var other = initRuntime(program, host)
   doAssert errorContains(proc() = other.setGlobal("answer$", value), "stale")
   doAssert errorContains(proc() = runtime.setGlobal("answer$", 1), "type")
@@ -312,4 +313,47 @@ c$ = right$(a$, 4)
   doAssert runtime.stringBytes == 6
   doAssert runtime.getStringData("second$") == "cdef"
 
+echo "Testing repeated string restarts and borrowed host access"
+block:
+  var host = initHost()
+  discard host.addData("incoming$", "host value")
+  var runtime: Runtime
+  let inspect: NumericHostProc = proc(args: openArray[Value]): Value =
+    ## Borrows a substring without constructing a Nim string.
+    runtime.withString(args[0], text):
+      doAssert text.len == 4 and text[0] == 'e' and text[3] == 'i'
+    toValue(1)
+  discard host.addFunction("inspect", 1, inspect)
+  let program = compile("""
+dim saved$(2)
+if turns = 0 then
+  saved$(0) = "persistent text"
+  saved$(1) = mid$(saved$(0), 2, 4)
+end if
+turns = turns + 1
+message$ = "turn " + str$(turns) + incoming$
+saved$(2) = message$
+ok = inspect(saved$(1))
+""", host)
+  runtime = initRuntime(program, host)
+  for i in 1 .. 1000:
+    runtime.restart()
+    discard runtime.run()
+    doAssert runtime.getGlobal("turns") == i
+    doAssert runtime.getStringArray("saved$", 0) == "persistent text"
+    doAssert runtime.getStringArray("saved$", 1) == "ersi"
+    doAssert runtime.getStringArray("saved$", 2) ==
+      "turn  " & $i & "host value"
+    doAssert runtime.getStringData("incoming$") == "host value"
+    doAssert runtime.stringCount < 32
+    doAssert runtime.stringBytes < 256
+  let empty = runtime.putString("")
+  runtime.withString(empty, text):
+    doAssert text.len == 0
+  runtime.reset()
+  doAssert errorContains(proc() =
+    runtime.withString(empty, text):
+      discard text.len
+  , "stale")
+
 echo "Native string tests passed"