From c2392d0ca30b8982185a3821be5b327d5edaa712 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Pawe=C5=82=20Sacawa?= <pawelsacawa@gmail.com>
Date: Thu, 10 Jun 2021 17:16:39 -0400
Subject: [PATCH] Fix: Patterns matching the empty string rejected

As observed in #86, fingers accepts a pattern accepting an empty string, such as `(token)?`, and this leads the `gawk` subprocess to loop indefinitely, allocated memory until it's eventually killed by the kernel.
This pr rejects such patterns, printing an error message.
---
 README.md         |  3 ++-
 scripts/config.sh | 17 ++++++++++++++++-
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index d6612b6..639e52a 100644
--- a/README.md
+++ b/README.md
@@ -128,7 +128,8 @@ set -g @fingers-pattern-1 'yolo'
 set -g @fingers-pattern-50 'whatever'
 ```
 
-Patterns are case insensitive, and grep's extended syntax ( ERE ) should be used.
+Patterns are case insensitive, and grep's extended syntax ( ERE ) should be used. Patterns
+matching the empty string are disallowed.
 `man grep` for more info.
 
 If the introduced regexp contains an error, an error will be shown when
diff --git a/scripts/config.sh b/scripts/config.sh
index b90df94..1939fcf 100755
--- a/scripts/config.sh
+++ b/scripts/config.sh
@@ -7,7 +7,6 @@ TMUX_PRINTER="$CONF_CURRENT_DIR/../vendor/tmux-printer/tmux-printer"
 
 declare -A fingers_defaults
 
-# TODO empty patterns are invalid
 function check_pattern() {
   echo "beep beep" | grep -e "$1" 2> /dev/null
 
@@ -18,6 +17,14 @@ function check_pattern() {
   fi
 }
 
+function check_matches_empty_string() {
+  if ! grep -e "$1" <<< "" >/dev/null; then
+    echo 0
+  else
+    echo 1
+  fi
+}
+
 function envify() {
   echo $1 | tr '[:lower:]' '[:upper:]' | sed "s/-/_/g"
 }
@@ -109,6 +116,14 @@ for pattern in "${PATTERNS_LIST[@]}" ; do
     PATTERNS_LIST[$i]="nope{4000}"
   fi
 
+  pattern_matches_empty=$(check_matches_empty_string "$pattern")
+
+  if [[ $pattern_matches_empty == 0 ]]; then
+    display_message "fingers-error: user defined pattern $pattern matched the empty string" 5000
+    PATTERNS_LIST[$i]="nope{4000}"
+  fi
+
+
   i=$((i + 1))
 done