From e5e1d4b53ed60d26c90e87441243dfb39b7ceb57 Mon Sep 17 00:00:00 2001
From: Martijn Dekker <martijn@inlv.org>
Date: Wed, 19 May 2021 00:02:49 +0200
Subject: [PATCH] Decrease SHLVL before doing 'exec' from main shell

Problem:

$ exec ksh
$ echo $SHLVL
2
$ exec ksh
$ echo $SHLVL
3
$ exec ksh
$ echo $SHLVL
4

...etc. SHLVL is supposed to acount the number of shell processes
that you need to exit before you get logged out. Since ksh was
replacing itself with a new shell in the same process using 'exec',
SHLVL should not increase.

src/cmd/ksh93/bltins/misc.c: b_exec():
- When about to replace the shell and we're not in a subshell,
  decrease SHLVL to cancel out a subsequent increase by the
  replacing shell. Bash and zsh also do this.
---
 NEWS                            | 4 ++++
 src/cmd/ksh93/bltins/misc.c     | 3 +++
 src/cmd/ksh93/include/version.h | 2 +-
 src/cmd/ksh93/sh.1              | 9 +++++++--
 4 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/NEWS b/NEWS
index 87e19b1cb..e0d06810e 100644
--- a/NEWS
+++ b/NEWS
@@ -3,6 +3,10 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2021-05-18:
+
+- Fixed SHLVL so that replacing ksh by itself (exec ksh) will not increase it.
+
 2021-05-13:
 
 - Fixed a bug with 'test -t 1' that was introduced on 2021-04-26:
diff --git a/src/cmd/ksh93/bltins/misc.c b/src/cmd/ksh93/bltins/misc.c
index 852ff7da6..a517100b2 100644
--- a/src/cmd/ksh93/bltins/misc.c
+++ b/src/cmd/ksh93/bltins/misc.c
@@ -161,6 +161,9 @@ int    b_exec(int argc,char *argv[], Shbltin_t *context)
 		if(job_close(logdata.sh) < 0)
 			return(1);
 #endif /* JOBS */
+		/* if the main shell is about to be replaced, decrease SHLVL to cancel out a subsequent increase */
+		if(!shgd->realsubshell)
+			(*SHLVL->nvalue.ip)--;
 		/* force bad exec to terminate shell */
 		pp = (struct checkpt*)logdata.sh->jmplist;
 		pp->mode = SH_JMPEXIT;
diff --git a/src/cmd/ksh93/include/version.h b/src/cmd/ksh93/include/version.h
index fa0e53090..420bc1910 100644
--- a/src/cmd/ksh93/include/version.h
+++ b/src/cmd/ksh93/include/version.h
@@ -21,7 +21,7 @@
 
 #define SH_RELEASE_FORK	"93u+m"		/* only change if you develop a new ksh93 fork */
 #define SH_RELEASE_SVER	"1.0.0-beta.2"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2021-05-13"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2021-05-18"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2021 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */
diff --git a/src/cmd/ksh93/sh.1 b/src/cmd/ksh93/sh.1
index c07a014b9..3c5ece6e2 100644
--- a/src/cmd/ksh93/sh.1
+++ b/src/cmd/ksh93/sh.1
@@ -1802,8 +1802,8 @@ be the value that was assigned plus the number of seconds since the assignment.
 .TP
 .SM
 .B SHLVL
-An integer variable the is incremented each time the shell
-is invoked and is exported.
+An integer variable that is incremented and exported
+each time the shell is invoked.
 If
 .SM
 .B SHLVL
@@ -6028,6 +6028,11 @@ is given,
 the command specified by
 the arguments is executed in place of this shell
 without creating a new process.
+The value of the
+.SM
+.B SHLVL
+environment variable is decreased by one,
+unless the shell replaced is a subshell.
 The
 .B \-c
 option causes the environment to be cleared before applying