Improve support of make autocompletion for huge Makefiles

completions/make

@@ -153,10 +153,72 @@ _make()
         fi
 
         local reset=$( shopt -po posix ); set +o posix # <(...)
-        COMPREPLY=( $( LC_ALL=C \
-            $1 -npq __BASH_MAKE_COMPLETION__=1 \
-                "${makef[@]}" "${makef_dir[@]}" .DEFAULT 2>/dev/null | \
-            command sed -nf <(_make_target_extract_script $mode "$cur") ) )
+
+        # there are two caches:
+        local cache_file=""         # for the output of make
+        local prefix_cache_file=""  # for the output of sed
+
+        # caching settings:
+        local cache_dir="$HOME/.cache_make_bash_completion"
+        local sed_threshold_in_millis="150" # otherwise, do not cache
+        local make_threshold_in_millis="50" # otherwise, do not cache
+
+        # Note:
+        # Caching is currently not implemented if "-C" or "-f" is used.
+        # In principle, there is no reason why it should not work,
+        # but as I do not use these features, I just skip it, here.
+        if [[ -z "${makef[@]}" && -z ${make_dir[@]} && -r "Makefile" ]] ; then
+            local cache_key=$( ( pwd && cat Makefile ) | md5sum | cut -f 1 -d ' ' )
+
+            # Currently, there is no cleanup mechanism, and there might
+            # be a smarter hashing strategy, too.
+            mkdir -p -- "$cache_dir"
+            cache_file="$cache_dir/make-bash-completion-${cache_key}.cache"
+            prefix_cache_file="$cache_dir/make-bash-completion_${cur}_${mode}_${cache_key}.cache"
+        fi
+
+        local prefix_filtered_result
+        if [[ -n "$prefix_cache_file" && -r "$prefix_cache_file" ]] ; then
+            prefix_filtered_result=$(cat -- "$prefix_cache_file")
+        else
+            local make_output
+            if [[ -n "$cache_file" && -r "$cache_file" ]] ; then
+                make_output=$(cat -- "$cache_file")
+            else
+                local before_make_nanos="$(date +%s%N)"
+                make_output="$( LC_ALL=C \
+                                make -npq __BASH_MAKE_COMPLETION__=1 \
+                                "${makef[@]}" "${makef_dir[@]}" .DEFAULT 2>/dev/null )"
+                local after_make_nanos="$(date +%s%N)"
+                if [[ -n "$cache_file" ]] && (( (($after_make_nanos - $before_make_nanos) / 1000000) > $make_threshold_in_millis )) ; then
+                    echo "$make_output" > "$cache_file"
+                fi
+            fi
+
+            local before_sed_nanos="$(date +%s%N)"
+            prefix_filtered_result=$( echo "$make_output" | \
+                                            command sed -nf <(_make_target_extract_script $mode "$cur") )
+            local after_sed_nanos="$(date +%s%N)"
+
+            if [[ -n "$prefix_cache_file" ]] && (( (( ${after_sed_nanos} - ${before_sed_nanos}) / 1000000) > ${sed_threshold_in_millis} )) ; then
+                echo "$prefix_filtered_result" > "$prefix_cache_file"
+            fi
+        fi
+
+        # Filter away all non-binaries and the source files, as
+        # otherwise, it can result in thousands of results,
+        # which are mostly uninteresting.
+        #
+        # Note:
+        # Filtering here with grep is almost certainly a hack.
+        # A better approach could be to change the sed expression
+        # in _make_target_extract_script. Maybe that would simplify
+        # the work that sed has to do and make it run faster
+        # (in my system, sed is the bottleneck).
+        #
+        COMPREPLY=( $( echo "$prefix_filtered_result" | \
+                             egrep -v '\.(o|obj|h|c|cpp)$') )
+
         $reset
 
         if [[ $mode != -d ]]; then