Fix glfwGetKeyName incorrectly emitting error

glfwGetKeyName emitted GLFW_INVALID_VALUE when passed GLFW_KEY_UNKNOWN
and any scancode not associated with a key token on that platform.

This causes physical keys with no associated key token to emit
GLFW_INVALID_VALUE when the key and scancode are passed directly from
the key event to glfwGetKeyName.  This breaks the promise made in the
reference documentation for glfwGetKeyName.

This commit removes that error for the whole range of valid scancodes.

Fixes #1785
Fixes #2214

This was adapted to 3.3-stable from
86bf5698ec.

CONTRIBUTORS.md

@@ -255,6 +255,7 @@ video tutorials.
  - Jay Weisskopf
  - Frank Wille
  - Richard A. Wilkes
+ - Andy Williams
  - Tatsuya Yatagawa
  - Ryogo Yoshimura
  - Rácz Zalán

README.md

@@ -123,6 +123,8 @@ information on what to include when reporting a bug.
 
 ## Changelog
 
+ - Bugfix: `glfwGetKeyName` emitted `GLFW_INVALID_VALUE` for scancodes with no
+   key token (#1785,#2214)
  - [Wayland] Bugfix: Terminating the library before showing a window could segfault
  - [Linux] Bugfix: `regfree´ was called on invalid data (#2464)
 

src/cocoa_window.m

@@ -1635,14 +1635,15 @@ const char* _glfwPlatformGetScancodeName(int scancode)
 {
     @autoreleasepool {
 
-    if (scancode < 0 || scancode > 0xff ||
-        _glfw.ns.keycodes[scancode] == GLFW_KEY_UNKNOWN)
+    if (scancode < 0 || scancode > 0xff)
     {
         _glfwInputError(GLFW_INVALID_VALUE, "Invalid scancode %i", scancode);
         return NULL;
     }
 
     const int key = _glfw.ns.keycodes[scancode];
+    if (key == GLFW_KEY_UNKNOWN)
+        return NULL;
 
     UInt32 deadKeyState = 0;
     UniChar characters[4];

src/win32_window.c

@@ -2191,14 +2191,19 @@ void _glfwPlatformSetCursorMode(_GLFWwindow* window, int mode)
 
 const char* _glfwPlatformGetScancodeName(int scancode)
 {
-    if (scancode < 0 || scancode > (KF_EXTENDED | 0xff) ||
-        _glfw.win32.keycodes[scancode] == GLFW_KEY_UNKNOWN)
+    int key;
+
+    if (scancode < 0 || scancode > (KF_EXTENDED | 0xff))
     {
         _glfwInputError(GLFW_INVALID_VALUE, "Invalid scancode %i", scancode);
         return NULL;
     }
 
-    return _glfw.win32.keynames[_glfw.win32.keycodes[scancode]];
+    key = _glfw.win32.keycodes[scancode];
+    if (key == GLFW_KEY_UNKNOWN)
+        return NULL;
+
+    return _glfw.win32.keynames[key];
 }
 
 int _glfwPlatformGetKeyScancode(int key)

src/wl_window.c

@@ -2575,8 +2575,7 @@ void _glfwPlatformSetCursorMode(_GLFWwindow* window, int mode)
 
 const char* _glfwPlatformGetScancodeName(int scancode)
 {
-    if (scancode < 0 || scancode > 255 ||
-        _glfw.wl.keycodes[scancode] == GLFW_KEY_UNKNOWN)
+    if (scancode < 0 || scancode > 255)
     {
         _glfwInputError(GLFW_INVALID_VALUE,
                         "Wayland: Invalid scancode %i",
@@ -2585,6 +2584,9 @@ const char* _glfwPlatformGetScancodeName(int scancode)
     }
 
     const int key = _glfw.wl.keycodes[scancode];
+    if (key == GLFW_KEY_UNKNOWN)
+        return NULL;
+
     const xkb_keycode_t keycode = scancode + 8;
     const xkb_layout_index_t layout =
         xkb_state_key_get_layout(_glfw.wl.xkb.state, keycode);

src/x11_window.c

@@ -2930,14 +2930,16 @@ const char* _glfwPlatformGetScancodeName(int scancode)
     if (!_glfw.x11.xkb.available)
         return NULL;
 
-    if (scancode < 0 || scancode > 0xff ||
-        _glfw.x11.keycodes[scancode] == GLFW_KEY_UNKNOWN)
+    if (scancode < 0 || scancode > 0xff)
     {
         _glfwInputError(GLFW_INVALID_VALUE, "Invalid scancode %i", scancode);
         return NULL;
     }
 
     const int key = _glfw.x11.keycodes[scancode];
+    if (key == GLFW_KEY_UNKNOWN)
+        return NULL;
+
     const KeySym keysym = XkbKeycodeToKeysym(_glfw.x11.display,
                                              scancode, _glfw.x11.xkb.group, 0);
     if (keysym == NoSymbol)