feat(fish): Enable left and right transience (#4204)

* feat(fish): Enable left and right transience

* Update README.md

* Mention limitation

1 files changed, 35 insertions, 0 deletions

diff --git a/docs/advanced-config/README.md b/docs/advanced-config/README.md
index e030cadf3..9718e94d9 100644
--- a/docs/advanced-config/README.md
+++ b/docs/advanced-config/README.md
@@ -71,6 +71,41 @@ end
 load(io.popen('starship init cmd'):read("*a"))()
 ```
 
+## TransientPrompt and TransientRightPrompt in Fish
+
+It is possible to replace the previous-printed prompt with a custom string. This
+is useful in cases where all the prompt information is not always needed. To enable
+this, run `enable_transience` in the shell session. To make it permanent, put
+this statement in your `~/.config/fish/config.fish`. Transience can be disabled on-the-fly with
+`disable_transience`.
+
+Note that in case of Fish, the transient prompt is only printed if the commandline is non-empty,
+and syntactically correct.
+
+- By default, the left side of input gets replaced with a bold-green `❯`. To customize this,
+  define a new function called `starship_transient_prompt_func`. For example, to
+  display Starship's `character` module here, you would do
+
+```fish
+function starship_transient_prompt_func
+  starship module character
+end
+starship init fish | source
+enable_transience
+```
+
+- By default, the right side of input is empty. To customize this, define a new
+  function called `starship_transient_rprompt_func`. For example, to display
+  the time at which the last command was started here, you would do
+
+```fish
+function starship_transient_rprompt_func
+  starship module time
+end
+starship init fish | source
+enable_transience
+```
+
 ## Custom pre-prompt and pre-execution Commands in Cmd
 
 Clink provides extremely flexible APIs to run pre-prompt and pre-exec commands