zsh: make sure entries in PATH and MANPATH are in a consistent order

config/zsh/.zprofile

@@ -1,4 +1,26 @@
-# General environment settings.
+have() {
+  command -v "$1" >/dev/null 2>&1
+}
+
+# Prepend $2 to variable $1 using $3 as separator, but only if $2 is not already
+# contained in $1. This is useful for prepending to PATH while avoiding
+# duplicates.
+prepend_unique() {
+  local var="$1" new="$2" sep="${3-:}"  # Default separator is colon.
+  local old="${(P)var}"
+
+  case "${sep}${old}${sep}" in
+    *"${sep}${new}${sep}"*)  # Skip duplicate.
+      ;;
+    "${sep}${sep}")  # Variable was empty, set without separator.
+      typeset -g $var="${new}"
+      ;;
+    *) # Prepend with separator.
+      typeset -g $var="${new}${sep}${old}"
+      ;;
+  esac
+}
+
 setup_environment() {
   export XDG_CACHE_HOME="${XDG_CACHE_HOME:-$HOME/.cache}"
   export XDG_CONFIG_HOME="${XDG_CONFIG_HOME:-$HOME/.config}"
@@ -14,15 +36,11 @@ setup_environment() {
   export LESS="-i -j.49 -M -R -z-2"
   export LESSHISTFILE="$XDG_DATA_HOME/less/history"
   export LESSHISTSIZE=1000
-  export LOCAL_PREFIX="/usr/local"
   export PAGER=less
   export PYTHONSTARTUP="$XDG_CONFIG_HOME/python/startup.py"
 }
 
-have() {
+setup_path_and_manpath() {
-  command -v "$1" >/dev/null 2>&1
-}
-
   # Prevent path_helper from messing with the PATH when starting tmux.
   #
   # Clearing PATH before path_helper executes (from /etc/profile) will prevent it
@@ -31,74 +49,59 @@ have() {
   #
   #   For details see: https://superuser.com/a/583502
   #
-setup_macos_path_helper() {
   [ "$(uname -s)" = "Darwin" ] && { PATH=""; source /etc/profile; }
+
+  local prefix="/usr/local"
+  have brew && prefix="$(brew --prefix)"
+
+  local custom_paths=(
+    "$prefix/opt/curl/bin"
+    "$prefix/bin"
+    "$HOME/.local/bin"
+    "$HOME/.bin"
+  )
+
+  local bindir=""
+  for bindir in $custom_paths; do
+    [ -d "$bindir" ] && prepend_unique PATH "$bindir"
+  done
+  export PATH
+
+  # Now that PATH is set, we should pick up all relevant man page locations, as
+  # for all directories ending in `<pathname>/bin` found in PATH, `manpath` will
+  # print the first existing directory of:
+  #   - `<pathname>/man`
+  #   - `<pathname>/../share/man`
+  #   - `<pathname>/../man`
+  have manpath && { MANPATH="$(unset MANPATH; manpath)"; export MANPATH; }
 }
 
-# Prepend $2 to variable $1 using $3 as separator, but only if $2 is not already
+# Some packages are installed by Homebrew in non-standard locations, in order to
-# contained in $1. This is useful for prepending to PATH while avoiding
+# prevent conflicts with their system versions.
-# duplicates.
+setup_brew_keg_only_packages() {
-prepend_unique() {
+  have brew || return
-  local var="$1"
-  local new="$2"
-  local sep="${3-:}"  # Default separator is colon.
-  local old="${(P)var}"
 
-  case "${sep}${old}${sep}" in
+  local packages=(
-    *"${sep}${new}${sep}"*)  # Skip duplicate.
+    make
-      ;;
+    grep
-    "${sep}${sep}")  # Variable was empty, set without separator.
+    gnu-tar
-      typeset -g $var="${new}"
+    gnu-sed
-      ;;
+    findutils
-    *) # Prepend with separator.
+    coreutils
-      typeset -g $var="${new}${sep}${old}"
+  )
-      ;;
+
-  esac
+  local prefix="$(brew --prefix)"
+  local pkg="" bindir="" mandir=""
+
+  for pkg in $packages; do
+    bindir="$prefix/opt/$pkg/libexec/gnubin"
+    [ -d "$bindir" ] && prepend_unique PATH "$bindir"
+
+    mandir="$prefix/opt/$pkg/libexec/gnuman"
+    [ -d "$mandir" ] && prepend_unique MANPATH "$mandir"
+  done
 }
 
-# Add custom bin dirs to PATH if they exist and are not already in PATH.
-setup_path() {
-  local dir=""
-  while read -r dir; do
-    [ -d "$dir" ] && prepend_unique PATH "${dir}"
-  done <<EOL
-    $LOCAL_PREFIX/bin
-    $LOCAL_PREFIX/opt/curl/bin
-    $LOCAL_PREFIX/opt/make/libexec/gnubin
-    $LOCAL_PREFIX/opt/findutils/libexec/gnubin
-    $LOCAL_PREFIX/opt/gnu-sed/libexec/gnubin
-    $LOCAL_PREFIX/opt/gnu-tar/libexec/gnubin
-    $LOCAL_PREFIX/opt/grep/libexec/gnubin
-    $LOCAL_PREFIX/opt/coreutils/libexec/gnubin
-    $HOME/.local/bin
-    $HOME/.bin
-EOL
-}
-
-# Prepend custom man directories to MANPATH if they exist, so that we get
-# correct man page entries when multiple versions of a command are
-# available.
-setup_manpath() {
-  local dir=""
-  # TODO: check if I really need the next line, `manpath` add ~600ms to startup
-  # have manpath && MANPATH="$(unset MANPATH; manpath)"
-  while read -r dir; do
-    [ -d "$dir" ] && prepend_unique MANPATH "${dir}"
-  done <<-EOL
-    $LOCAL_PREFIX/share/man
-    $LOCAL_PREFIX/opt/curl/share/man
-    $LOCAL_PREFIX/opt/make/libexec/gnuman
-    $LOCAL_PREFIX/opt/findutils/libexec/gnuman
-    $LOCAL_PREFIX/opt/gnu-sed/libexec/gnuman
-    $LOCAL_PREFIX/opt/gnu-tar/libexec/gnuman
-    $LOCAL_PREFIX/opt/grep/libexec/gnuman
-    $LOCAL_PREFIX/opt/coreutils/libexec/gnuman
-    $HOME/.local/share/man
-EOL
-}
-
-# These checks have to be done after PATH manipulation above so we can find
-# installed programs if they are in the added paths.
 setup_tools() {
   have nvim && EDITOR="nvim"
   [ -z $EDITOR ] && have vim && EDITOR="vim"
@@ -138,10 +141,9 @@ setup_local_profile() {
 
 # zmodload zsh/zprof
 setup_environment
-setup_macos_path_helper
+setup_path_and_manpath
-setup_path && export PATH
+setup_brew_keg_only_packages
-setup_manpath && export MANPATH
+setup_tools  # NOTE: this must be done _after_ `setup_environment`.
-setup_tools
 setup_wsl_display
 setup_local_profile
 # zprof