Add set --no-event

This allows running `set` without triggering any event handlers.

That is useful, for example, if you want to set a variable in an event
handler for that variable - we could do it, for example, in the
fish_user_path or fish_key_bindings handlers.

This is something the `block` builtin was supposed to be for, but it
never really worked because it only allows suppressing the event for
the duration, they would fire later. See #9030.

Because it is possible to abuse this, we only have a long-option so
that people see what is up.

doc_src/cmds/set.rst

@@ -9,7 +9,7 @@ Synopsis
 .. synopsis::
 
     set
-    set (-f | --function) (-l | --local) (-g | --global) (-U | --universal)
+    set (-f | --function) (-l | --local) (-g | --global) (-U | --universal) [--no-event]
     set [-Uflg] NAME [VALUE ...]
     set [-Uflg] NAME[[INDEX ...]] [VALUE ...]
     set (-a | --append) [-flgU] NAME VALUE ...
@@ -102,6 +102,11 @@ Further options:
     It shows the scopes the given variables are set in, along with the values in each and whether or not it is exported.
     No other flags can be used with this option.
 
+**--no-event**
+    Don't generate a variable change event when setting or erasing a variable.
+    We recommend using this carefully because the event handlers are usually set up for a reason.
+    Possible uses include modifying the variable inside a variable handler.
+
 **-L** or **--long**
     Do not abbreviate long values when printing set variables.
 

src/builtins/set.rs

@@ -43,6 +43,7 @@ struct Options {
     append: bool,
     prepend: bool,
     preserve_failure_exit_status: bool,
+    no_event: bool,
 }
 
 impl Default for Options {
@@ -65,6 +66,7 @@ impl Default for Options {
             append: false,
             prepend: false,
             preserve_failure_exit_status: true,
+            no_event: false,
         }
     }
 }
@@ -98,6 +100,7 @@ impl Options {
         /// Values used for long-only options.
         const PATH_ARG: char = 1 as char;
         const UNPATH_ARG: char = 2 as char;
+        const NO_EVENT_ARG: char = 3 as char;
         // Variables used for parsing the argument list. This command is atypical in using the "+"
         // (REQUIRE_ORDER) option for flag parsing. This is not typical of most fish commands. It means
         // we stop scanning for flags when the first non-flag argument is seen.
@@ -118,6 +121,7 @@ impl Options {
             wopt(L!("prepend"), NoArgument, 'p'),
             wopt(L!("path"), NoArgument, PATH_ARG),
             wopt(L!("unpath"), NoArgument, UNPATH_ARG),
+            wopt(L!("no-event"), NoArgument, NO_EVENT_ARG),
             wopt(L!("help"), NoArgument, 'h'),
         ];
 
@@ -148,6 +152,7 @@ impl Options {
                 'u' => opts.unexport = true,
                 PATH_ARG => opts.pathvar = true,
                 UNPATH_ARG => opts.unpathvar = true,
+                NO_EVENT_ARG => opts.no_event = true,
                 'U' => opts.universal = true,
                 'L' => opts.shorten_ok = false,
                 'S' => {
@@ -341,13 +346,18 @@ fn handle_env_return(retval: EnvStackSetResult, cmd: &wstr, key: &wstr, streams:
 /// description of the problem to stderr.
 fn env_set_reporting_errors(
     cmd: &wstr,
+    opts: &Options,
     key: &wstr,
     scope: EnvMode,
     list: Vec<WString>,
     streams: &mut IoStreams,
     parser: &Parser,
 ) -> EnvStackSetResult {
-    let retval = parser.set_var_and_fire(key, scope | EnvMode::USER, list);
+    let retval = if opts.no_event {
+        parser.set_var(key, scope | EnvMode::USER, list)
+    } else {
+        parser.set_var_and_fire(key, scope | EnvMode::USER, list)
+    };
     // If this returned OK, the parser already fired the event.
     handle_env_return(retval, cmd, key, streams);
     retval
@@ -776,7 +786,7 @@ fn erase(
                 if retval != EnvStackSetResult::ENV_NOT_FOUND {
                     handle_env_return(retval, cmd, split.varname, streams);
                 }
-                if retval == EnvStackSetResult::ENV_OK {
+                if retval == EnvStackSetResult::ENV_OK && !opts.no_event {
                     event::fire(parser, Event::variable_erase(split.varname.to_owned()));
                 }
             } else {
@@ -785,8 +795,15 @@ fn erase(
                     return STATUS_CMD_ERROR;
                 };
                 let result = erased_at_indexes(var.as_list().to_owned(), split.indexes);
-                retval =
-                    env_set_reporting_errors(cmd, split.varname, scope, result, streams, parser);
+                retval = env_set_reporting_errors(
+                    cmd,
+                    opts,
+                    split.varname,
+                    scope,
+                    result,
+                    streams,
+                    parser,
+                );
             }
 
             // Set $status to the last error value.
@@ -951,7 +968,8 @@ fn set_internal(
     };
 
     // Set the value back in the variable stack and fire any events.
-    let retval = env_set_reporting_errors(cmd, split.varname, scope, new_values, streams, parser);
+    let retval =
+        env_set_reporting_errors(cmd, opts, split.varname, scope, new_values, streams, parser);
 
     if retval == EnvStackSetResult::ENV_OK {
         warn_if_uvar_shadows_global(cmd, opts, split.varname, streams, parser);

src/parser.rs

@@ -805,6 +805,11 @@ impl Parser {
         res
     }
 
+    /// Cover of vars().set(), without firing events
+    pub fn set_var(&self, key: &wstr, mode: EnvMode, vals: Vec<WString>) -> EnvStackSetResult {
+        self.vars().set(key, mode, vals)
+    }
+
     /// Update any universal variables and send event handlers.
     /// If `always` is set, then do it even if we have no pending changes (that is, look for
     /// changes from other fish instances); otherwise only sync if this instance has changed uvars.

tests/checks/set.fish

@@ -965,4 +965,33 @@ set -e undefined[..1]
 set -l negative_oob 1 2 3
 set -q negative_oob[-10..1]
 
+# --no-event
+
+function onevent --on-variable nonevent
+    echo ONEVENT $argv $nonevent
+end
+
+set -g nonevent bar
+set -e nonevent
+
+# CHECK: ONEVENT VARIABLE SET nonevent bar
+# CHECK: ONEVENT VARIABLE ERASE nonevent
+
+set -g --no-event nonevent 2
+set -e --no-event nonevent
+set -S nonevent
+
+set -g --no-event nonevent 3
+set -e nonevent
+# CHECK: ONEVENT VARIABLE ERASE nonevent
+
+set -g nonevent 4
+# CHECK: ONEVENT VARIABLE SET nonevent 4
+set -e --no-event nonevent
+
+set -l nonevent 4
+set -e nonevent
+# CHECK: ONEVENT VARIABLE SET nonevent
+# CHECK: ONEVENT VARIABLE ERASE nonevent
+
 exit 0