Allow deciding if a command should be saved to history (fish-shell#10302)

 Call fish_should_add_to_history to see if a command should be saved

If it returns 0, it will be saved, if it returns anything else, it
will be ephemeral.

It gets the right-trimmed text as the argument.

If it doesn't exist, we do the historical behavior of checking for a
leading space.

That means you can now turn that off by defining a
`fish_should_add_to_history` that just doesn't check it.

documentation based on fish-shell#9298

Author: faho

doc_src/cmds/fish_should_add_to_history.rst

@@ -0,0 +1,57 @@
+.. _cmd-fish_should_add_to_history:
+
+fish_should_add_to_history - decide whether a command should be added to the history
+=================================================================================
+
+Synopsis
+--------
+
+.. synopsis::
+
+    fish_should_add_to_history
+
+::
+
+  function fish_should_add_to_history
+      ...
+  end
+
+
+Description
+-----------
+
+The ``fish_should_add_to_history`` function is executed before fish adds a command to history, and its return status decides whether that is done.
+
+If it returns 0, the command is stored in history, when it returns anything else, it is not. In the latter case the command can still be recalled for one command.
+
+The first argument to ``fish_should_add_to_history`` is the commandline. History is added *before* a command is run, so e.g. :envvar:`status` can't be checked. This is so commands that don't finish like :doc:`exec` and long-running commands are available in new sessions immediately.
+
+If ``fish_should_add_to_history`` doesn't exist, fish will save a command to history unless it starts with a space. If it does exist, this function takes over all of the duties, so commands starting with space are saved unless ``fish_should_add_to_history`` says otherwise.
+
+Example
+-------
+
+A simple example:
+
+::
+
+    function fish_should_add_to_history
+        for cmd in vault mysql ls
+             string match -qr "^$cmd" -- $argv; and return 1
+        end
+        return 0
+    end
+
+This refuses to store any immediate "vault", "mysql" or "ls" calls. Commands starting with space would be stored.
+
+::
+
+    function fish_should_add_to_history
+        # I don't want `git pull`s in my history when I'm in a specific repository
+        if string match -qr '^git pull'
+        and string match -qr "^/home/me/my-secret-project/" -- (pwd -P)
+            return 1
+        end
+   
+        return 0
+    end

src/reader.rs

@@ -4674,6 +4674,25 @@ impl ReaderData {
         }
     }
 
+    fn should_add_to_history(&mut self, text: &wstr) -> bool {
+        let parser = self.parser();
+        if !function::exists(L!("fish_should_add_to_history"), parser) {
+            // Historical behavior, if the command starts with a space we don't save it.
+            return text.as_char_slice()[0] != ' ';
+        }
+
+        let mut cmd: WString = L!("fish_should_add_to_history ").into();
+        cmd.push_utfstr(&escape(text));
+        let _not_interactive = scoped_push_replacer(
+            |new_value| std::mem::replace(&mut parser.libdata_mut().pods.is_interactive, new_value),
+            false,
+        );
+
+        let ret = exec_subshell(&cmd, parser, None, /*apply_exit_status=*/ false);
+
+        ret == STATUS_CMD_OK.unwrap()
+    }
+
     // Add the current command line contents to history.
     fn add_to_history(&mut self) {
         if self.conf.in_silent_mode {
@@ -4692,9 +4711,8 @@ impl ReaderData {
         self.history.remove_ephemeral_items();
 
         if !text.is_empty() {
-            // Mark this item as ephemeral if there is a leading space (#615).
-            let mode = if text.as_char_slice()[0] == ' ' {
-                // Leading spaces are ephemeral (#615).
+            // Mark this item as ephemeral if should_add_to_history says no (#615).
+            let mode = if !self.should_add_to_history(&text) {
                 PersistenceMode::Ephemeral
             } else if in_private_mode(self.vars()) {
                 PersistenceMode::Memory

tests/pexpects/history.py

@@ -178,3 +178,27 @@
 expect_prompt()
 sendline("history search --exact 'echo after' | cat")
 expect_prompt("\r\n")
+
+# Check history filtering
+# We store anything that starts with "echo ephemeral".
+sendline("function fish_should_add_to_history; string match -q 'echo ephemeral*' -- $argv; and return 2; return 0; end")
+expect_prompt("")
+# Check that matching the line works
+# (fish_should_add_to_history is itself stored in history so we match "ephemeral!" to avoid it)
+sendline("echo ephemeral! line")
+expect_prompt("ephemeral! line")
+sendline("echo nonephemeral! line")
+expect_prompt("nonephemeral! line")
+sendline("true")
+expect_prompt()
+sendline("echo a; history search '*ephemeral!*' | cat; echo b")
+expect_prompt("a\r\necho nonephemeral! line\r\nb\r\n")
+
+# If fish_should_add_to_history exists, it will completely take over,
+# so even lines with spaces are stored
+sendline(" echo spaced")
+expect_prompt("spaced")
+sendline("true")
+expect_prompt()
+sendline("echo a; history search '*spaced*' | cat; echo b")
+expect_prompt("a\r\n echo spaced\r\nb\r\n")