Remove flex version checks

Remove the flex version checks from configure and meson.  The cutoff
versions are all so ancient that this is no longer relevant, and what
the actual cutoff should be is a bit fuzzy.

This also removes the ancient behavior that configure would also
accept a "lex" program if it is actuall flex.  This aligns the check
with meson in this respect.

For future reference, as of this commit, these are relevant flex
versions:

- The hard required minimum is flex 2.5.34 as of commit b1ef48980dd,
  but this has not actually been tested.

- Prior to this, the minimum enforced by configure/meson was flex
  2.5.35, which is the oldest present in the buildfarm right now.

- As of commit 6fdd5d95634, the oldest version that will compile
  without warnings due to flex-generated code is flex 2.5.36.

- The oldest version that probably still has some practical relevance
  is flex 2.5.37, which ships with CentOS/RHEL 7.

Discussion: https://www.postgresql.org/message-id/1a204ccd-7ae6-478c-a431-407b5c48ccc6@eisentraut.org

5 files changed, 66 insertions, 100 deletions

diff --git a/config/programs.m4 b/config/programs.m4
index 490ec9fe9f5..7b55c2664a6 100644
--- a/config/programs.m4
+++ b/config/programs.m4
@@ -59,57 +59,16 @@ AC_SUBST(BISONFLAGS)
 # PGAC_PATH_FLEX
 # --------------
 # Look for Flex, set the output variable FLEX to its path if found.
-# Reject versions before 2.5.35 (the earliest version in the buildfarm
-# as of 2022). Also find Flex if its installed under `lex', but do not
-# accept other Lex programs.
 
 AC_DEFUN([PGAC_PATH_FLEX],
-[AC_CACHE_CHECK([for flex], pgac_cv_path_flex,
-[# Let the user override the test
-if test -n "$FLEX"; then
-  pgac_cv_path_flex=$FLEX
-else
-  pgac_save_IFS=$IFS
-  IFS=$PATH_SEPARATOR
-  for pgac_dir in $PATH; do
-    IFS=$pgac_save_IFS
-    if test -z "$pgac_dir" || test x"$pgac_dir" = x"."; then
-      pgac_dir=`pwd`
-    fi
-    for pgac_prog in flex lex; do
-      pgac_candidate="$pgac_dir/$pgac_prog"
-      if test -f "$pgac_candidate" \
-        && $pgac_candidate --version </dev/null >/dev/null 2>&1
-      then
-        echo '%%'  > conftest.l
-        if $pgac_candidate -t conftest.l 2>/dev/null | grep FLEX_SCANNER >/dev/null 2>&1; then
-          pgac_flex_version=`$pgac_candidate --version 2>/dev/null`
-          if echo "$pgac_flex_version" | sed ['s/[.a-z]/ /g'] | $AWK '{ if ([$]1 == 2 && ([$]2 > 5 || ([$]2 == 5 && [$]3 >= 35))) exit 0; else exit 1;}'
-          then
-            pgac_cv_path_flex=$pgac_candidate
-            break 2
-          else
-            AC_MSG_ERROR([
-*** The installed version of Flex, $pgac_candidate, is too old to use with PostgreSQL.
-*** Flex version 2.5.35 or later is required, but this is $pgac_flex_version.])
-          fi
-        fi
-      fi
-    done
-  done
-  rm -f conftest.l lex.yy.c
-  : ${pgac_cv_path_flex=no}
-fi
-])[]dnl AC_CACHE_CHECK
-
-if test x"$pgac_cv_path_flex" = x"no"; then
+[PGAC_PATH_PROGS(FLEX, flex)
+if test -z "$FLEX"; then
   AC_MSG_ERROR([flex not found])
-else
-  FLEX=$pgac_cv_path_flex
-  pgac_flex_version=`$FLEX --version 2>/dev/null`
-  AC_MSG_NOTICE([using $pgac_flex_version])
 fi
 
+pgac_flex_version=`$FLEX --version 2>/dev/null`
+AC_MSG_NOTICE([using $pgac_flex_version])
+
 AC_SUBST(FLEX)
 AC_SUBST(FLEXFLAGS)
 ])# PGAC_PATH_FLEX
diff --git a/configure b/configure
index a0b5e10ca39..ceeef9b0915 100755
--- a/configure
+++ b/configure
@@ -9931,59 +9931,68 @@ if test -z "$BISON"; then
 fi
 
 
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for flex" >&5
-$as_echo_n "checking for flex... " >&6; }
-if ${pgac_cv_path_flex+:} false; then :
+if test -z "$FLEX"; then
+  for ac_prog in flex
+do
+  # Extract the first word of "$ac_prog", so it can be a program name with args.
+set dummy $ac_prog; ac_word=$2
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for $ac_word" >&5
+$as_echo_n "checking for $ac_word... " >&6; }
+if ${ac_cv_path_FLEX+:} false; then :
   $as_echo_n "(cached) " >&6
 else
-  # Let the user override the test
-if test -n "$FLEX"; then
-  pgac_cv_path_flex=$FLEX
-else
-  pgac_save_IFS=$IFS
-  IFS=$PATH_SEPARATOR
-  for pgac_dir in $PATH; do
-    IFS=$pgac_save_IFS
-    if test -z "$pgac_dir" || test x"$pgac_dir" = x"."; then
-      pgac_dir=`pwd`
-    fi
-    for pgac_prog in flex lex; do
-      pgac_candidate="$pgac_dir/$pgac_prog"
-      if test -f "$pgac_candidate" \
-        && $pgac_candidate --version </dev/null >/dev/null 2>&1
-      then
-        echo '%%'  > conftest.l
-        if $pgac_candidate -t conftest.l 2>/dev/null | grep FLEX_SCANNER >/dev/null 2>&1; then
-          pgac_flex_version=`$pgac_candidate --version 2>/dev/null`
-          if echo "$pgac_flex_version" | sed 's/[.a-z]/ /g' | $AWK '{ if ($1 == 2 && ($2 > 5 || ($2 == 5 && $3 >= 35))) exit 0; else exit 1;}'
-          then
-            pgac_cv_path_flex=$pgac_candidate
-            break 2
-          else
-            as_fn_error $? "
-*** The installed version of Flex, $pgac_candidate, is too old to use with PostgreSQL.
-*** Flex version 2.5.35 or later is required, but this is $pgac_flex_version." "$LINENO" 5
-          fi
-        fi
-      fi
-    done
+  case $FLEX in
+  [\\/]* | ?:[\\/]*)
+  ac_cv_path_FLEX="$FLEX" # Let the user override the test with a path.
+  ;;
+  *)
+  as_save_IFS=$IFS; IFS=$PATH_SEPARATOR
+for as_dir in $PATH
+do
+  IFS=$as_save_IFS
+  test -z "$as_dir" && as_dir=.
+    for ac_exec_ext in '' $ac_executable_extensions; do
+  if as_fn_executable_p "$as_dir/$ac_word$ac_exec_ext"; then
+    ac_cv_path_FLEX="$as_dir/$ac_word$ac_exec_ext"
+    $as_echo "$as_me:${as_lineno-$LINENO}: found $as_dir/$ac_word$ac_exec_ext" >&5
+    break 2
+  fi
+done
   done
-  rm -f conftest.l lex.yy.c
-  : ${pgac_cv_path_flex=no}
+IFS=$as_save_IFS
+
+  ;;
+esac
+fi
+FLEX=$ac_cv_path_FLEX
+if test -n "$FLEX"; then
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $FLEX" >&5
+$as_echo "$FLEX" >&6; }
+else
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
+$as_echo "no" >&6; }
 fi
 
+
+  test -n "$FLEX" && break
+done
+
+else
+  # Report the value of FLEX in configure's output in all cases.
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for FLEX" >&5
+$as_echo_n "checking for FLEX... " >&6; }
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $FLEX" >&5
+$as_echo "$FLEX" >&6; }
 fi
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv_path_flex" >&5
-$as_echo "$pgac_cv_path_flex" >&6; }
-if test x"$pgac_cv_path_flex" = x"no"; then
+
+if test -z "$FLEX"; then
   as_fn_error $? "flex not found" "$LINENO" 5
-else
-  FLEX=$pgac_cv_path_flex
-  pgac_flex_version=`$FLEX --version 2>/dev/null`
-  { $as_echo "$as_me:${as_lineno-$LINENO}: using $pgac_flex_version" >&5
-$as_echo "$as_me: using $pgac_flex_version" >&6;}
 fi
 
+pgac_flex_version=`$FLEX --version 2>/dev/null`
+{ $as_echo "$as_me:${as_lineno-$LINENO}: using $pgac_flex_version" >&5
+$as_echo "$as_me: using $pgac_flex_version" >&6;}
+
 
 
 
diff --git a/doc/src/sgml/installation.sgml b/doc/src/sgml/installation.sgml
index ebdb5b3bc2d..271615e4a65 100644
--- a/doc/src/sgml/installation.sgml
+++ b/doc/src/sgml/installation.sgml
@@ -100,10 +100,10 @@
        <primary>yacc</primary>
       </indexterm>
 
-      <application>Flex</application> 2.5.35 or later and
-      <application>Bison</application> 2.3 or later are required.  Other
-      <application>lex</application> and <application>yacc</application>
-      programs cannot be used.
+      <application>Flex</application> and <application>Bison</application> are
+      required.  Other <application>lex</application> and
+      <application>yacc</application> programs cannot be used.
+      <application>Bison</application> needs to be at least version 2.3.
      </para>
     </listitem>
 
@@ -3811,10 +3811,8 @@ make: *** [postgres] Error 1
         <productname>Flex</productname></term>
        <listitem>
        <para>
-        <productname>Bison</productname> and <productname>Flex</productname> are
-        required.  Only <productname>Bison</productname> versions 2.3 and later
-        will work. <productname>Flex</productname> must be version 2.5.35 or later.
-        Binaries can be downloaded from <ulink
+        Binaries for <productname>Bison</productname> and
+        <productname>Flex</productname> can be downloaded from <ulink
         url="https://github.com/lexxmark/winflexbison"></ulink>.
        </para>
        </listitem>
diff --git a/meson.build b/meson.build
index cfd654d2916..32fc89f3a4b 100644
--- a/meson.build
+++ b/meson.build
@@ -334,7 +334,7 @@ endif
 # External programs
 perl = find_program(get_option('PERL'), required: true, native: true)
 python = find_program(get_option('PYTHON'), required: true, native: true)
-flex = find_program(get_option('FLEX'), native: true, version: '>= 2.5.35')
+flex = find_program(get_option('FLEX'), native: true)
 bison = find_program(get_option('BISON'), native: true, version: '>= 2.3')
 sed = find_program(get_option('SED'), 'sed', native: true, required: false)
 prove = find_program(get_option('PROVE'), native: true, required: false)
diff --git a/src/backend/utils/misc/guc-file.l b/src/backend/utils/misc/guc-file.l
index c0ecb8b2ce2..11a1e2a3f9f 100644
--- a/src/backend/utils/misc/guc-file.l
+++ b/src/backend/utils/misc/guc-file.l
@@ -302,7 +302,7 @@ record_config_file_error(const char *errmsg,
 /*
  * Flex fatal errors bring us here.  Stash the error message and jump back to
  * ParseConfigFp().  Assume all msg arguments point to string constants; this
- * holds for flex 2.5.35 (earliest we support). Otherwise, we would need to
+ * holds for all currently known flex versions. Otherwise, we would need to
  * copy the message.
  *
  * We return "int" since this takes the place of calls to fprintf().