don't allow problematic string and array assignments anymore, improve error messages.

In certain cases you will need to use string.copy() explicitly to overwrite strings with new strings.

compiler/res/prog8lib/compression.p8

@@ -2,6 +2,8 @@
 
 compression {
 
+    %option no_symbol_prefixing, ignore_unused
+
     sub encode_rle_outfunc(uword data, uword size, uword output_function, bool is_last_block) {
         ; -- Compress the given data block using ByteRun1 aka PackBits RLE encoding.
         ;    output_function = address of a routine that gets a byte arg in A,

compiler/src/prog8/compiler/astprocessing/AstChecker.kt

@@ -550,10 +550,8 @@ internal class AstChecker(private val program: Program,
         fun checkType(target: AssignTarget, value: Expression, augmentable: Boolean) {
             val targetDt = target.inferType(program)
             val valueDt = value.inferType(program)
-            if(valueDt.isKnown && !(valueDt isAssignableTo targetDt)) {
+            if(valueDt.isKnown && !(valueDt isAssignableTo targetDt) && !targetDt.isIterable) {
-                if(targetDt.isIterable)
+                if(!(valueDt istype DataType.STR && targetDt istype DataType.UWORD)) {
-                    errors.err("cannot assign value to string or array", value.position)
-                else if(!(valueDt istype DataType.STR && targetDt istype DataType.UWORD)) {
                     if(targetDt.isUnknown) {
                         if(target.identifier?.targetStatement(program)!=null)
                             errors.err("target datatype is unknown", target.position)
@@ -1844,6 +1842,12 @@ internal class AstChecker(private val program: Program,
         else if(targetDatatype==DataType.BOOL && sourceDatatype!=DataType.BOOL) {
             errors.err("type of value $sourceDatatype doesn't match target $targetDatatype", position)
         }
+        else if(targetDatatype==DataType.STR) {
+            if(sourceDatatype==DataType.UWORD)
+                errors.err("can't assign UWORD to STR. If the source is a string and you actually want to overwrite the target string, use an explicit string.copy(src,tgt) instead.", position)
+            else
+                errors.err("type of value $sourceDatatype doesn't match target $targetDatatype", position)
+        }
         else {
             errors.err("type of value $sourceDatatype doesn't match target $targetDatatype", position)
         }

compiler/src/prog8/compiler/astprocessing/StatementReorderer.kt

@@ -210,15 +210,11 @@ internal class StatementReorderer(
         val targetType = assignment.target.inferType(program)
 
         if(targetType.isArray && valueType.isArray) {
-            if (assignment.value is ArrayLiteral) {
+            checkCopyArrayValue(assignment)
-                errors.err("cannot assign array literal here, use separate assignment per element", assignment.position)
-            } else {
-                return copyArrayValue(assignment)
-            }
         }
 
         if(!assignment.isAugmentable) {
-            if (valueType.isString && (targetType istype DataType.STR || targetType istype DataType.ARRAY_B || targetType istype DataType.ARRAY_UB)) {
+            if (valueType istype DataType.STR && targetType istype DataType.STR) {
                 // replace string assignment by a call to stringcopy
                 return copyStringValue(assignment)
             }
@@ -247,18 +243,22 @@ internal class StatementReorderer(
         return noModifications
     }
 
-    private fun copyArrayValue(assign: Assignment): List<IAstModification> {
+    private fun checkCopyArrayValue(assign: Assignment) {
         val identifier = assign.target.identifier!!
         val targetVar = identifier.targetVarDecl(program)!!
 
         if(targetVar.arraysize==null) {
             errors.err("array has no defined size", assign.position)
-            return noModifications
+            return
+        }
+
+        if(assign.value is ArrayLiteral) {
+            return  // invalid assignment of literals will be reported elsewhere
         }
 
         if(assign.value !is IdentifierReference) {
             errors.err("invalid array value to assign to other array", assign.value.position)
-            return noModifications
+            return
         }
         val sourceIdent = assign.value as IdentifierReference
         val sourceVar = sourceIdent.targetVarDecl(program)!!
@@ -273,7 +273,6 @@ internal class StatementReorderer(
                 errors.err("element size mismatch", assign.position)
             }
         }
-        return noModifications
     }
 
     private fun copyStringValue(assign: Assignment): List<IAstModification> {

docs/source/programming.rst

@@ -286,8 +286,7 @@ Arrays
 ^^^^^^
 Array types are also supported. They can be formed from a list of booleans, bytes, words, floats, or addresses of other variables
 (such as explicit address-of expressions, strings, or other array variables) - values in an array literal
-always have to be constants. Putting variables inside an array has to be done on a value-by-value basis.
+always have to be constants. Here are some examples of arrays::
-Here are some examples of arrays::
 
     byte[10]  array                   ; array of 10 bytes, initially set to 0
     byte[]  array = [1, 2, 3, 4]      ; initialize the array, size taken from value
@@ -300,6 +299,7 @@ Here are some examples of arrays::
     value = array[3]            ; the fourth value in the array (index is 0-based)
     char = string[4]            ; the fifth character (=byte) in the string
     char = string[-2]           ; the second-to-last character in the string (Python-style indexing from the end)
+    flags = [false, true]       ; reset all flags in the array
 
 .. note::
     Right now, the array should be small enough to be indexable by a single byte index.
@@ -312,9 +312,8 @@ Note that the various keywords for the data type and variable type (``byte``, ``
 can't be used as *identifiers* elsewhere. You can't make a variable, block or subroutine with the name ``byte``
 for instance.
 
-
+It's possible to assign an array to another array; this will overwrite all elements in the target
-It's possible to assign a new array to another array, this will overwrite all elements in the original
+array with those in the source array. The number and types of elements have to match for this to work!
-array with those in the value array. The number and types of elements have to match.
 For large arrays this is a slow operation because every element is copied over. It should probably be avoided.
 
 Using the ``in`` operator you can easily check if a value is present in an array,
@@ -650,10 +649,6 @@ Assignment statements assign a single value to a target variable or memory locat
 Augmented assignments (such as ``aa += xx``) are also available, but these are just shorthands
 for normal assignments (``aa = aa + xx``).
 
-Only variables of type byte, word and float can be assigned a new value.
-It's not possible to set a new value to string or array variables etc, because they get allocated
-a fixed amount of memory which will not change.  (You *can* change the value of elements in a string or array though).
-
 It is possible to "chain" assignments: ``x = y = z = 42``, this is just a shorthand
 for the three individual assignments with the same value 42.
 

docs/source/todo.rst

@@ -1,6 +1,12 @@
 TODO
 ====
 
+Don't allow assigning str to array!
+Don't allow assigning array to str!
+Don't allow assigning a word to an array or string!
+
+Put palette fade to white / black in.
+
 Regenerate skeleton doc files.
 
 Improve register load order in subroutine call args assignments:
@@ -12,6 +18,7 @@ Maybe this routine can be made more intelligent.  See usesOtherRegistersWhileEva
 Future Things and Ideas
 ^^^^^^^^^^^^^^^^^^^^^^^
 
+- The string assignment footgun should be removed in favor of just calling string.copy explicitly.   Get rid of sys.internal_stringcopy asm routine.  Fix docs too.
 - Improve the SublimeText syntax file for prog8, you can also install this for 'bat': https://github.com/sharkdp/bat?tab=readme-ov-file#adding-new-syntaxes--language-definitions
 - Can we support signed % (remainder) somehow?
 - Don't add "random" rts to %asm blocks but instead give a warning about it? (but this breaks existing behavior that others already depend on... command line switch? block directive?)

examples/test.p8

@@ -1,46 +1,30 @@
 %import textio
+%import string
 %zeropage basicsafe
 
 main {
     sub start() {
-        routine(11,22,33)
+        str name1 = "irmen"
-        txt.nl()
+        str name2 = "other"
-        cx16.r0 = callfar2(0, &routine, 11, 22, 33, true)
+        bool[2] flags = [true, false]
-        txt.nl()
-        txt.print_uwhex(cx16.r0, true)
-        txt.nl()
-        cx16.r0 = callfar(0, &routine, 11*256 + 22)
-        txt.nl()
-        txt.print_uwhex(cx16.r0, true)
-        txt.nl()
-    }
 
-    asmsub routine(ubyte v1 @A, ubyte v2 @X, ubyte v3 @Y) -> uword @AY {
+        txt.print(name1)
-        %asm {{
+        txt.nl()
-            sta  cx16.r8L
+        name1 = name2
-            stx  cx16.r9L
+        txt.print(name1)
-            sty  cx16.r10L
+        txt.nl()
-            lda  #0
+        flags = [false, true]
-            rol  a
-            sta  cx16.r11L
 
-            lda  cx16.r8L
+        ubyte[10] array
-            jsr  txt.print_ub
+        ubyte[10] array2
-            lda  #' '
+
-            jsr  txt.chrout
+        void string.copy(name2, name1)
-            lda  cx16.r9L
+        array = array2
-            jsr  txt.print_ub
+        name2 = "zzz"
-            lda  #' '
+        array = [1,2,3,4,5,6,7,8,9,10]
-            jsr  txt.chrout
+        ;; array = cx16.r0
-            lda  cx16.r10L
+        ;; array = name1
-            jsr  txt.print_ub
+        ;; name1 = array
-            lda  #' '
+        ;; name1 = cx16.r0
-            jsr  txt.chrout
-            lda  cx16.r11L
-            jsr  txt.print_ub
-            lda  #$31
-            ldy  #$ea
-            rts
-        }}
     }
 }