Add a python virtualenv style prompt prefix.

If the user sets the env variable `BUILDWITH_SHOW_PROMPT`,
the shell prompt is prefixed by the currently activated mozconfig:

```sh
cd ~/gecko
buildwith release
(release) ./mach build
```
This prefix is only shown if the shell is inside a gecko repository.

Author: jnjaeschke

README.md

@@ -72,6 +72,22 @@ For example, if you put this in your ~/.bashrc file (or equivalent):
 buildwith will also set the MOZCONFIG environment variable in launchctl (useful when running Android Studio).
 All occurences of ``#1`` will be replaced by the path to the mozconfig file.
 
+#### prompt prefix
+
+Similar to Python virtualenvs, you can display the active mozconfig name as a prefix in your shell prompt.
+This prefix only appears when you are inside a gecko repository. To enable this feature, add to your ~/.bashrc file (or equivalent):
+
+    export BUILDWITH_SHOW_PROMPT=1
+
+The default format is `(mozconfig_name) ` but you can customize it with:
+
+    export BUILDWITH_PROMPT_FORMAT="[%s] "
+
+The `%s` will be replaced with the mozconfig name. For example, if you activate a config named "debug" while inside a gecko repository, your prompt will show `(debug) ` or `[debug] ` depending on your format setting.
+
+The prompt automatically appears when you `cd` into a gecko repository and disappears when you leave it.
+Gecko repositories are detected by the presence of `mach` or `moz.configure` files.
+
 #### mozconfig template
 
 When you make a new mozconfig, it will be populated with some basic build commands and the name of the mozconfig

src/scripts/mozconfigwrapper.sh

@@ -9,6 +9,36 @@ function mozconfigwrapper_buildwith_home {
     fi
 }
 
+# Detect if current directory is inside a gecko repository
+function mozconfigwrapper_is_in_gecko {
+    # Search up the directory tree for gecko markers
+    typeset current="$PWD"
+    while [ "$current" != "/" ]; do
+        if [ -f "$current/mach" ] || [ -f "$current/moz.configure" ]; then
+            return 0
+        fi
+        current=$(dirname "$current")
+    done
+
+    return 1
+}
+
+# Generate prompt prefix if BUILDWITH_SHOW_PROMPT is enabled
+function mozconfigwrapper_prompt {
+    # Only show prompt if explicitly enabled
+    if [ -z "$BUILDWITH_SHOW_PROMPT" ]; then
+        return
+    fi
+
+    # Only show if we have an active mozconfig and we're in a gecko repo
+    if [ -n "$MOZCONFIG" ] && mozconfigwrapper_is_in_gecko; then
+        typeset mozconfig_name=$(basename "$MOZCONFIG")
+        typeset format="${BUILDWITH_PROMPT_FORMAT:-(%s) }"
+        # Replace %s with mozconfig name
+        printf "$format" "$mozconfig_name"
+    fi
+}
+
 function buildwith {
     mozconfigwrapper_buildwith_home
     typeset name="$1"
@@ -75,7 +105,15 @@ function rmmozconfig {
     fi
 
     mozconfig="$BUILDWITH_HOME/$name"
-    rm $mozconfig
+
+    # If we're removing the active mozconfig, unset it
+    if [ "$MOZCONFIG" = "$mozconfig" ]
+    then
+        unset MOZCONFIG
+        rm -f "$BUILDWITH_HOME/.active"
+    fi
+
+    rm "$mozconfig"
     echo "Removed: $mozconfig"
 }
 
@@ -108,8 +146,46 @@ function mozconfigwrapper_list_mozconfigs {
         | (unset GREP_OPTIONS; command \egrep -v '^\*$') 2>/dev/null
 }
 
+# Store original PS1 for zsh
+_MOZCONFIGWRAPPER_ORIGINAL_PS1=""
+
+# Set up prompt integration if BUILDWITH_SHOW_PROMPT is enabled
+function mozconfigwrapper_setup_prompt {
+    if [ -z "$BUILDWITH_SHOW_PROMPT" ]; then
+        return
+    fi
+
+    if [ -n "$BASH" ]; then
+        # For bash, we modify PS1 to include our prompt function
+        # Only modify if not already present
+        if [[ "$PS1" != *'$(mozconfigwrapper_prompt)'* ]]; then
+            export PS1="\$(mozconfigwrapper_prompt)$PS1"
+        fi
+    elif [ -n "$ZSH_VERSION" ]; then
+        # For zsh, save the original PS1 and add to precmd_functions array
+        if [ -z "$_MOZCONFIGWRAPPER_ORIGINAL_PS1" ]; then
+            _MOZCONFIGWRAPPER_ORIGINAL_PS1="$PS1"
+        fi
+        if [[ ! " ${precmd_functions[@]} " =~ " mozconfigwrapper_precmd " ]]; then
+            precmd_functions+=(mozconfigwrapper_precmd)
+        fi
+    fi
+}
+
+# Zsh precmd hook to update PS1
+function mozconfigwrapper_precmd {
+    # Reconstruct PS1 from the original, preserving prompt expansions
+    typeset prefix=$(mozconfigwrapper_prompt)
+    if [ -n "$prefix" ]; then
+        PS1="${prefix}${_MOZCONFIGWRAPPER_ORIGINAL_PS1}"
+    else
+        PS1="$_MOZCONFIGWRAPPER_ORIGINAL_PS1"
+    fi
+}
+
 mozconfigwrapper_buildwith_home
 mozconfigwrapper_setup_tab_completion
+mozconfigwrapper_setup_prompt
 
 if [ -f "$BUILDWITH_HOME/.active" ]
 then