Ignore unrepresentable characters when typing

In 94ad6da, we changed it so typing
characters outside of CC's codepage were replaced with '?' rather than
ignored. This can be quite annoying for non-European users (where latin1
isn't very helpful!), so it makes sense to revert this change.

See discussion in #860 for more context.

projects/common/src/client/java/dan200/computercraft/client/gui/widgets/TerminalWidget.java

@@ -72,7 +72,7 @@ public TerminalWidget(Terminal terminal, InputHandler computer, int x, int y) {
     @Override
     public boolean charTyped(char ch, int modifiers) {
         var terminalChar = StringUtil.unicodeToTerminal(ch);
-        if (StringUtil.isTypableChar(terminalChar)) computer.charTyped(terminalChar);
+        if (StringUtil.isTypableChar(terminalChar)) computer.charTyped((byte) terminalChar);
         return true;
     }
 

projects/core/src/main/java/dan200/computercraft/core/util/StringUtil.java

@@ -18,24 +18,25 @@ private StringUtil() {
      * Convert a Unicode character to a terminal one.
      *
      * @param chr The Unicode character.
-     * @return The terminal character.
+     * @return The terminal character. This is either in the range [0, 255] (if a valid character) or {@code -1} if
+     * it cannot be mapped to CC's charset.
      */
-    public static byte unicodeToTerminal(int chr) {
+    public static int unicodeToTerminal(int chr) {
         // ASCII and latin1 map to themselves
         if (chr == 0 || chr == '\t' || chr == '\n' || chr == '\r' || (chr >= ' ' && chr <= '~') || (chr >= 160 && chr <= 255)) {
-            return (byte) chr;
+            return chr;
         }
 
         // Teletext block mosaics are *fairly* contiguous.
-        if (chr >= 0x1FB00 && chr <= 0x1FB13) return (byte) (chr + (129 - 0x1fb00));
-        if (chr >= 0x1FB14 && chr <= 0x1FB1D) return (byte) (chr + (150 - 0x1fb14));
+        if (chr >= 0x1FB00 && chr <= 0x1FB13) return chr + (129 - 0x1fb00);
+        if (chr >= 0x1FB14 && chr <= 0x1FB1D) return chr + (150 - 0x1fb14);
 
         // Everything else is just a manual lookup. For now, we just use a big switch statement, which we spin into a
         // separate function to hopefully avoid inlining it here.
         return unicodeToCraftOsFallback(chr);
     }
 
-    private static byte unicodeToCraftOsFallback(int c) {
+    private static int unicodeToCraftOsFallback(int c) {
         return switch (c) {
             case 0x263A -> 1;
             case 0x263B -> 2;
@@ -64,8 +65,8 @@ private static byte unicodeToCraftOsFallback(int c) {
             case 0x25B2 -> 30;
             case 0x25BC -> 31;
             case 0x1FB99 -> 127;
-            case 0x258C -> (byte) 149;
-            default -> '?';
+            case 0x258C -> 149;
+            default -> -1;
         };
     }
 
@@ -76,8 +77,8 @@ private static byte unicodeToCraftOsFallback(int c) {
      * @param chr The character to check.
      * @return Whether this character can be typed.
      */
-    public static boolean isTypableChar(byte chr) {
-        return chr != 0 && chr != '\r' && chr != '\n';
+    public static boolean isTypableChar(int chr) {
+        return chr >= 0 && chr <= 255 && chr != 0 && chr != '\r' && chr != '\n';
     }
 
     private static boolean isAllowedInLabel(char c) {
@@ -110,8 +111,9 @@ public static ByteBuffer getClipboardString(String clipboard) {
         var iterator = clipboard.codePoints().iterator();
         while (iterator.hasNext() && idx <= output.length) {
             var chr = unicodeToTerminal(iterator.next());
-            if (!isTypableChar(chr)) break;
-            output[idx++] = chr;
+            if (chr < 0) continue; // Strip out unconvertible characters
+            if (!isTypableChar(chr)) break; // Stop at untypable ones.
+            output[idx++] = (byte) chr;
         }
 
         return ByteBuffer.wrap(output, 0, idx).asReadOnlyBuffer();

projects/standalone/src/main/java/cc/tweaked/standalone/InputState.java

@@ -51,7 +51,7 @@ public InputState(Computer computer) {
 
     public void onCharEvent(int codepoint) {
         var terminalChar = StringUtil.unicodeToTerminal(codepoint);
-        if (StringUtil.isTypableChar(terminalChar)) ComputerEvents.charTyped(computer, terminalChar);
+        if (StringUtil.isTypableChar(terminalChar)) ComputerEvents.charTyped(computer, (byte) terminalChar);
     }
 
     public void onKeyEvent(long window, int key, int action, int modifiers) {