[PATCH] Re: regexp-replace and ^, word boundary or look-behind operators

[Stephane Chazelas <stephane.chazelas@gmail.com>]

2019-12-17 07:38:46 +0000, Stephane Chazelas:
> 2019-12-16 21:27:06 +0000, Stephane Chazelas:
> [...]
> > PCRE should be OK, so it could be just a matter of
> > exposing it via the pcre_match builtin
> [...]
> 
> D'oh, it's there already with the -b, -n options.
> 
> I'll try and suggest a regexp-replace improvement using that.
[...]

There's another issue in that the zero-width matches cause
infinite loops. Here's my first attempt at fixing those issues
(also fixing a few issues in the zpgrep example functions while
I'm at it):

diff --git a/Doc/Zsh/contrib.yo b/Doc/Zsh/contrib.yo
index d32ba018d..61e6a434f 100644
--- a/Doc/Zsh/contrib.yo
+++ b/Doc/Zsh/contrib.yo
@@ -4301,6 +4301,9 @@ and arithmetic expressions which will be replaced:  in particular, a
 reference to tt($MATCH) will be replaced by the text matched by the pattern.
 
 The return status is 0 if at least one match was performed, else 1.
+
+Note that if not using PCRE, using the tt(^) or word boundary operators
+(where available) may not work properly.
 )
 findex(run-help)
 item(tt(run-help) var(cmd))(
diff --git a/Functions/Example/zpgrep b/Functions/Example/zpgrep
index 8b1edaa1c..556e58cd6 100644
--- a/Functions/Example/zpgrep
+++ b/Functions/Example/zpgrep
@@ -2,24 +2,31 @@
 #
 
 zpgrep() {
-local file pattern
+local file pattern ret
 
 pattern=$1
 shift
+ret=1
 
 if ((! ARGC)) then
 	set -- -
 fi
 
-pcre_compile $pattern
+zmodload zsh/pcre || return
+pcre_compile -- "$pattern"
 pcre_study
 
 for file
 do
 	if [[ "$file" == - ]] then
-		while read -u0 buf; do pcre_match $buf && print $buf; done
+		while IFS= read -ru0 buf; do
+			pcre_match -- "$buf" && ret=0 && print -r -- "$buf"
+		done
 	else
-		while read -u0 buf; do pcre_match $buf && print $buf; done < "$file"
+		while IFS= read -ru0 buf; do
+			pcre_match -- "$buf" && ret=0 && print -r -- "$buf"
+		done < "$file"
 	fi
 done
+return "$ret"
 }
diff --git a/Functions/Misc/regexp-replace b/Functions/Misc/regexp-replace
index dec105524..41ea9d79e 100644
--- a/Functions/Misc/regexp-replace
+++ b/Functions/Misc/regexp-replace
@@ -8,36 +8,79 @@
 # $ and backtick substitutions; in particular, $MATCH will be replaced
 # by the portion of the string matched by the regular expression.
 
-integer pcre
+# we use positional parameters instead of variables to avoid
+# clashing with the user's variable. Make sure we start with 3 and only
+# 3 elements:
+argv=("$1" "$2" "$3")
 
-[[ -o re_match_pcre ]] && pcre=1
+# $4 records whether pcre is enabled as that information would otherwise
+# be lost after emulate -L zsh
+4=0
+[[ -o re_match_pcre ]] && 4=1
 
 emulate -L zsh
-(( pcre )) && setopt re_match_pcre
-
-# $4 is the string to be matched
-4=${(P)1}
-# $5 is the final string
-5=
-# 6 indicates if we made a change
-6=
+
+
 local MATCH MBEGIN MEND
 local -a match mbegin mend
 
-while [[ -n $4 ]]; do
-  if [[ $4 =~ $2 ]]; then
-    # append initial part and subsituted match
-    5+=${4[1,MBEGIN-1]}${(e)3}
-    # truncate remaining string
-    4=${4[MEND+1,-1]}
-    # indicate we did something
-    6=1
-  else
-    break
-  fi
-done
-5+=$4
-
-eval ${1}=${(q)5}
-# status 0 if we did something, else 1.
-[[ -n $6 ]]
+if (( $4 )); then
+  # if using pcre, we're using pcre_match and a running offset
+  # That's needed for ^, \A, \b, and look-behind operators to work
+  # properly.
+
+  zmodload zsh/pcre || return 2
+  pcre_compile -- "$2" && pcre_study || return 2
+
+  # $4 is the current *byte* offset, $5, $6 reserved for later
+  4=0 5= 6=1
+
+  local ZPCRE_OP IFS=' '
+  while pcre_match -b -n $4 -- "${(P)1}"; do
+    # append offsets and computed replacement to the array
+    argv+=($=ZPCRE_OP ${(e)3})
+
+    # for 0-width matches, increase offset by 1 to avoid
+    # infinite loop
+    4=$((argv[-2] + (argv[-3] == argv[-2])))
+  done
+
+  (($# > 6)) || return # no match
+
+  set +o multibyte
+
+  # $5 contains the result, $6 the current offset
+  for 2 3 4 in "$@[7,-1]"; do
+    5+=${(P)1[$6,$2]}$4
+    6=$(($3 + 1))
+  done
+  5+=${(P)1[$6,-1]}
+else
+  # in ERE, we can't use an offset so ^, (and \<, \b, \B, [[:<:]] where
+  # available) won't work properly.
+
+  # $4 is the string to be matched
+  4=${(P)1}
+
+  while [[ -n $4 ]]; do
+    if [[ $4 =~ $2 ]]; then
+      # append initial part and substituted match
+      5+=${4[1,MBEGIN-1]}${(e)3}
+      # truncate remaining string
+      if ((MEND < MBEGIN)); then
+        # zero-width match, skip one character for the next match
+        ((MEND++))
+	5+=${4[1]}
+      fi
+      4=${4[MEND+1,-1]}
+      # indicate we did something
+      6=1
+    else
+      break
+    fi
+  done
+  [[ -n $6 ]] || return # no match
+  5+=$4
+fi
+
+eval $1=\$5