[PATCHv2] [bug] $SHLVL decremented for the last command of a subshell

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

2016-08-29 18:55:05 -0700, Bart Schaefer:
> On Aug 29,  4:51pm, Stephane Chazelas wrote:
> }
> } I think the change below should be enough (also condensed the 2
> } "if"s below (unrelated)):
> 
> This looks fine, although I think we generally keep the braces on the
> "if" body whenever there is more than one line following -- even if
> some of those lines are comments.
> 
> Either that or move the comment above the "if".

How about this (factorised the !subsh some more comments and
added some test cases):

diff --git a/Src/exec.c b/Src/exec.c
index 9b24d38..2e251b9 100644
--- a/Src/exec.c
+++ b/Src/exec.c
@@ -3694,12 +3694,15 @@ execcmd(Estate state, int input, int output, int how, int last1)
 		restore_params(restorelist, removelist);
 
 	} else {
-	    if (!forked)
-		setiparam("SHLVL", --shlvl);
-	    if (do_exec) {
+	    if (!subsh) {
+	        /* for either implicit or explicit "exec", decrease $SHLVL
+		 * as we're now done as a shell */
+		if (!forked)
+		    setiparam("SHLVL", --shlvl);
+
 		/* If we are exec'ing a command, and we are not *
 		 * in a subshell, then save the history file.   */
-		if (!subsh && isset(RCS) && interact && !nohistsave)
+		if (do_exec && isset(RCS) && interact && !nohistsave)
 		    savehistfile(NULL, 1, HFILE_USE_OPTIONS);
 	    }
 	    if (type == WC_SIMPLE || type == WC_TYPESET) {
diff --git a/Test/D04parameter.ztst b/Test/D04parameter.ztst
index 0630079..75ace5a 100644
--- a/Test/D04parameter.ztst
+++ b/Test/D04parameter.ztst
@@ -1718,6 +1718,24 @@
 >2
 >2
 
+  SHLVL=1
+  $ZTST_testdir/../Src/zsh -fc 'sh -c "echo \$SHLVL"'
+  $ZTST_testdir/../Src/zsh -fc '(sh -c "echo \$SHLVL")'
+  $ZTST_testdir/../Src/zsh -fc '( (sh -c "echo \$SHLVL"))'
+0:SHLVL decremented upon implicit exec optimisation
+>1
+>1
+>1
+
+  SHLVL=1
+  $ZTST_testdir/../Src/zsh -fc '(sh -c "echo \$SHLVL"); exit'
+  $ZTST_testdir/../Src/zsh -fc '(exec sh -c "echo \$SHLVL"); exit'
+  $ZTST_testdir/../Src/zsh -fc '( (sh -c "echo \$SHLVL"); exit)'
+0:SHLVL not decremented upon exec in subshells
+>2
+>2
+>2
+
 # The following tests the return behaviour of parsestr/parsestrnoerr
   alias param-test-alias='print $'\''\x45xpanded in substitution'\' 
   param='$(param-test-alias)'