feat: implement `cmd_duration` for bash (#144)

2 files changed, 72 insertions, 13 deletions

diff --git a/docs/config/README.md b/docs/config/README.md
index 0c92e9361..e3d759fff 100644
--- a/docs/config/README.md
+++ b/docs/config/README.md
@@ -119,11 +119,16 @@ The `cmd_duration` module shows how long the last command took to execute.
 The module will be shown only if the command took longer than two seconds, or
 the `min_time` config value, if it exists.
 
-::: warning NOTE
-Command duration is currently not supported in `bash`. See
-[this issue](https://github.com/starship/starship/issues/124) for more details.
+::: warning Do Not Hook the DEBUG trap in Bash
+If you are running Starship in `bash`, do not hook the `DEBUG` trap after running
+`eval $(starship init $0)`, or this module **will** break.
 :::
 
+Bash users who need preexec-like functionality can use
+[rcaloras's bash_preexec framework](https://github.com/rcaloras/bash-preexec).
+Simply define the arrays `preexec_functions` and `precmd_functions` before 
+running `eval $(starship init $0)`, and then proceed as normal.
+
 ### Options
 
 | Variable   | Default | Description                         |
diff --git a/src/init.rs b/src/init.rs
index 16d466df2..d366bc1b8 100644
--- a/src/init.rs
+++ b/src/init.rs
@@ -52,23 +52,74 @@ pub fn init(shell_name: &str) {
     }
 }
 
-/* Bash does not currently support command durations (see issue #124) for details
-https://github.com/starship/starship/issues/124
+/*
+ For bash: we need to manually hook functions ourself: PROMPT_COMMAND will exec
+   right before the prompt is drawn, and any function trapped by DEBUG will exec
+   before a command is run.
 
-We need to quote the output of `$(jobs -p | wc -l)` since MacOS `wc` leaves
-giant spaces in front of the number (e.g. "    3"), which messes up the
-word-splitting. Instead, quote the whole thing, then let Rust do the whitespace
-trimming within the jobs module.
+   There is a preexec/precmd framework for bash out there: if we find the
+   appropriate variables set, assume we are using that framework:
+   https://github.com/rcaloras/bash-preexec
+
+   Bash quirk: DEBUG is triggered whenever a command is executed, even if that
+   command is part of a pipeline. To avoid only timing the last part of a pipeline,
+   we only start the timer if no timer has been started since the last prompt draw,
+   tracked by the variable PREEXEC_READY. Similarly, only draw timing info if
+   STARSHIP_START_TIME is defined, in case preexec was interrupted.
+
+   Finally, to work around existing DEBUG traps in the absence of a preexec-like,
+   we parse out the name of the old DEBUG hook, then make a new function which
+   calls both that function and our starship hooks. We don't do this for
+   PROMPT_COMMAND because that would probably result in two prompts.
+
+   We need to quote the output of `$(jobs -p | wc -l)` since MacOS `wc` leaves
+   giant spaces in front of the number (e.g. "    3"), which messes up the
+   word-splitting. Instead, quote the whole thing, then let Rust do the whitespace
+   trimming within the jobs module
 */
 
+/*
+Note to programmers: this and the zsh init will be evaluated on a single line.
+Use semicolons, avoid comments, and generally think like all newlines will be
+deleted.
+*/
 const BASH_INIT: &str = r##"
+starship_preexec() {
+    if [ "$PREEXEC_READY" = "true" ]; then
+        PREEXEC_READY=false;
+        STARSHIP_START_TIME=$(date +%s);
+    fi
+};
 starship_precmd() {
-        PS1="$(starship prompt --status=$? --jobs="$(jobs -p | wc -l)")";
+    STATUS=$?;
+    if [[ $STARSHIP_START_TIME ]]; then
+        STARSHIP_END_TIME=$(date +%s);
+        STARSHIP_DURATION=$((STARSHIP_END_TIME - STARSHIP_START_TIME));
+        PS1="$(starship prompt --status=$STATUS --jobs="$(jobs -p | wc -l)" --cmd-duration=$STARSHIP_DURATION)";
+        unset STARSHIP_START_TIME;
+    else
+        PS1="$(starship prompt --status=$STATUS --jobs="$(jobs -p | wc -l)")";
+    fi;
+    PREEXEC_READY=true;
 };
-PROMPT_COMMAND=starship_precmd;
+if [[ $preexec_functions ]]; then
+    preexec_functions+=(starship_preexec);
+    precmd_functions+=(starship_precmd);
+    STARSHIP_START_TIME=$(date +%s);
+else
+    dbg_trap="$(trap -p DEBUG | cut -d' ' -f3 | tr -d \')";
+    if [[ -z "$dbg_trap" ]]; then
+        trap starship_preexec DEBUG;
+    elif [[ "$dbg_trap" != "starship_preexec" && "$dbg_trap" != "starship_preexec_all" ]]; then
+        function starship_preexec_all(){
+            $dbg_trap; starship_preexec;
+        };
+        trap starship_preexec_all DEBUG;
+    fi;
+    PROMPT_COMMAND=starship_precmd;
+    STARSHIP_START_TIME=$(date +%s);
+fi;
 "##;
-/* TODO: Once warning/error system is implemented in starship, print a warning
-if starship will not be printing timing due to DEBUG clobber error */
 
 /* For zsh: preexec_functions and precmd_functions provide preexec/precmd in a
    way that lets us avoid clobbering them.
@@ -80,6 +131,9 @@ if starship will not be printing timing due to DEBUG clobber error */
 
    To fix this, only pass the time if STARSHIP_START_TIME is defined, and unset
    it after passing the time, so that we only measure actual commands.
+
+   We need to quote the output of the jobs command for the same reason as
+   bash.
 */
 
 const ZSH_INIT: &str = r##"