Unref gpio.trig callbacks when type=INTR_DISABLE (#3072)

Fixes #2880

Author: tomsci

components/modules/gpio.c

@@ -139,7 +139,7 @@ static int lgpio_read (lua_State *L)
 static int lgpio_trig (lua_State *L)
 {
   int gpio = luaL_checkint (L, 1);
-  int intr_type = luaL_checkint (L, 2);
+  int intr_type = luaL_optint (L, 2, GPIO_INTR_DISABLE);
   if (!lua_isnoneornil (L, 3))
     luaL_checkanyfunction (L, 3);
 
@@ -156,7 +156,15 @@ static int lgpio_trig (lua_State *L)
   }
 
   // Set/update interrupt callback
-  if (!lua_isnoneornil (L, 3))
+
+  // For compatibility with esp8266 API, passing in a non-zero intr_type and a
+  // nil callback preserves any existing callback that has been set.
+  if (intr_type == GPIO_INTR_DISABLE)
+  {
+    luaL_unref (L, LUA_REGISTRYINDEX, gpio_cb_refs[gpio]);
+    gpio_cb_refs[gpio] = LUA_NOREF;
+  }
+  else if (!lua_isnoneornil (L, 3))
   {
     luaL_unref (L, LUA_REGISTRYINDEX, gpio_cb_refs[gpio]);
     gpio_cb_refs[gpio] = luaL_ref (L, LUA_REGISTRYINDEX);
@@ -165,7 +173,7 @@ static int lgpio_trig (lua_State *L)
   // Disable interrupt while reconfiguring
   check_err (L, gpio_intr_disable (gpio));
 
-  if (gpio_cb_refs[gpio] == LUA_NOREF)
+  if (intr_type == GPIO_INTR_DISABLE)
   {
     check_err (L, gpio_set_intr_type (gpio, GPIO_INTR_DISABLE));
     check_err (L, gpio_isr_handler_remove (gpio));

docs/modules/gpio.md

@@ -67,17 +67,18 @@ Read digital GPIO pin value.
 Establish or clear a callback function to run on interrupt for a GPIO.
 
 #### Syntax
-`gpio.trig(pin, type [, callback])`
+`gpio.trig(pin [, type [, callback]])`
 
 #### Parameters
 - `pin`, see [GPIO Overview](#gpio-overview)
 - `type` trigger type, one of
+    - `gpio.INTR_DISABLE` or `nil` to disable interrupts on this pin (in which case `callback` is ignored and should be `nil` or omitted)
     - `gpio.INTR_UP` for trigger on rising edge
     - `gpio.INTR_DOWN` for trigger on falling edge
     - `gpio.INTR_UP_DOWN` for trigger on both edges
     - `gpio.INTR_LOW` for trigger on low level
     - `gpio.INTR_HIGH` for trigger on high level
-- `callback` optional function to be called when trigger fires, trigger is disabled when omitted. Parameters are:
+- `callback` optional function to be called when trigger fires. If `nil` or omitted (and `type` is not `gpio.INTR_DISABLE`) then any previously-set callback will continue to be used. Parameters are:
     - `pin`
     - `level`