Merge branch 'zandra/stdlib/optional-callbacks/OTP-13801'

* zandra/stdlib/optional-callbacks/OTP-13801:
  wx: make wx_object callbacks optional
  stdlib: Make gen_fsm callbacks optional
  stdlib: Make gen_event callbacks optional
  stdlib: Make gen_server callbacks optional

3 files changed, 55 insertions, 0 deletions

diff --git a/lib/stdlib/doc/src/gen_event.xml b/lib/stdlib/doc/src/gen_event.xml
index 42e952fd46..56cb7974a2 100644
--- a/lib/stdlib/doc/src/gen_event.xml
+++ b/lib/stdlib/doc/src/gen_event.xml
@@ -579,6 +579,13 @@ gen_event:stop             ----->  Module:terminate/2
         <v>Extra = term()</v>
       </type>
       <desc>
+        <note>
+          <p>This callback is optional, so callback modules need not export it.
+            If a release upgrade/downgrade with <c>Change={advanced,Extra}</c>
+            specified in the <c>.appup</c> file is made when <c>code_change/3</c>
+            isn't implemented the event handler will crash with an <c>undef</c> error
+            reason.</p>
+        </note>
         <p>This function is called for an installed event handler that
           is to update its internal state during a release
           upgrade/downgrade, that is, when the instruction
@@ -759,6 +766,12 @@ gen_event:stop             ----->  Module:terminate/2
         <v>&nbsp;&nbsp;Id = term()</v>
       </type>
       <desc>
+        <note>
+          <p>This callback is optional, so callback modules need not
+            export it. The <c>gen_event</c> module provides a default
+            implementation of this function that logs about the unexpected
+            <c>Info</c> message, drops it and returns <c>{noreply, State}</c>.</p>
+        </note>
         <p>This function is called for each installed event handler when
           an event manager receives any other message than an event or
           a synchronous request (or a system message).</p>
@@ -815,6 +828,11 @@ gen_event:stop             ----->  Module:terminate/2
         <v>&nbsp;Args = Reason = Term = term()</v>
       </type>
       <desc>
+        <note>
+          <p>This callback is optional, so callback modules need not
+            export it. The <c>gen_event</c> module provides a default
+            implementation without cleanup.</p>
+        </note>
         <p>Whenever an event handler is deleted from an event manager,
           this function is called. It is to be the opposite of
           <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>
diff --git a/lib/stdlib/doc/src/gen_fsm.xml b/lib/stdlib/doc/src/gen_fsm.xml
index 719ab2b558..691a039e34 100644
--- a/lib/stdlib/doc/src/gen_fsm.xml
+++ b/lib/stdlib/doc/src/gen_fsm.xml
@@ -562,6 +562,13 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
         <v>Extra = term()</v>
       </type>
       <desc>
+        <note>
+          <p>This callback is optional, so callback modules need not export it.
+            If a release upgrade/downgrade with <c>Change={advanced,Extra}</c>
+            specified in the <c>appup</c> file is made when <c>code_change/4</c>
+            isn't implemented the process will crash with an <c>undef</c> exit
+            reason.</p>
+        </note>
         <p>This function is called by a <c>gen_fsm</c> process when it is to
           update its internal state data during a release upgrade/downgrade,
           that is, when instruction <c>{update,Module,Change,...}</c>,
@@ -686,6 +693,13 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
         <v>&nbsp;Reason = normal | term()</v>
       </type>
       <desc>
+        <note>
+          <p>This callback is optional, so callback modules need not
+            export it. The <c>gen_fsm</c> module provides a default
+            implementation of this function that logs about the unexpected
+            <c>Info</c> message, drops it and returns
+            <c>{next_state, StateName, StateData}</c>.</p>
+        </note>
         <p>This function is called by a <c>gen_fsm</c> process when it receives
           any other message than a synchronous or asynchronous event (or a
           system message).</p>
@@ -899,6 +913,11 @@ gen_fsm:sync_send_all_state_event -----> Module:handle_sync_event/4
         <v>StateData = term()</v>
       </type>
       <desc>
+        <note>
+          <p>This callback is optional, so callback modules need not
+            export it. The <c>gen_fsm</c> module provides a default
+            implementation without cleanup.</p>
+        </note>
         <p>This function is called by a <c>gen_fsm</c> process when it is about
           to terminate. It is to be the opposite of
           <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>
diff --git a/lib/stdlib/doc/src/gen_server.xml b/lib/stdlib/doc/src/gen_server.xml
index 662076b5f0..4540449792 100644
--- a/lib/stdlib/doc/src/gen_server.xml
+++ b/lib/stdlib/doc/src/gen_server.xml
@@ -504,6 +504,13 @@ gen_server:abcast     -----> Module:handle_cast/2
         <v>Reason = term()</v>
       </type>
       <desc>
+        <note>
+          <p>This callback is optional, so callback modules need not export it.
+            If a release upgrade/downgrade with <c>Change={advanced,Extra}</c>
+            specified in the <c>appup</c> file is made when <c>code_change/3</c>
+            isn't implemented the process will crash with an <c>undef</c> exit
+            reason.</p>
+        </note>
         <p>This function is called by a <c>gen_server</c> process when it is
           to update its internal state during a release upgrade/downgrade,
           that is, when the instruction <c>{update,Module,Change,...}</c>,
@@ -690,6 +697,12 @@ gen_server:abcast     -----> Module:handle_cast/2
         <v>&nbsp;Reason = normal | term()</v>
       </type>
       <desc>
+        <note>
+          <p>This callback is optional, so callback modules need not
+            export it. The <c>gen_server</c> module provides a default
+            implementation of this function that logs about the unexpected
+            <c>Info</c> message, drops it and returns <c>{noreply, State}</c>.</p>
+        </note>
         <p>This function is called by a <c>gen_server</c> process when a
           time-out occurs or when it receives any other message than a
           synchronous or asynchronous request (or a system message).</p>
@@ -750,6 +763,11 @@ gen_server:abcast     -----> Module:handle_cast/2
         <v>State = term()</v>
       </type>
       <desc>
+        <note>
+          <p>This callback is optional, so callback modules need not
+            export it. The <c>gen_server</c> module provides a default
+            implementation without cleanup.</p>
+        </note>
         <p>This function is called by a <c>gen_server</c> process when it is
           about to terminate. It is to be the opposite of
           <seealso marker="#Module:init/1"><c>Module:init/1</c></seealso>