[PATCH?] Nofork and removing newlines

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

On Tue, Feb 27, 2024 at 12:53 PM Bart Schaefer
<schaefer@xxxxxxxxxxxxxxxx> wrote:
>
> The intent was to have ${ ... } act more like parameter substitution.
> It might be possible/reasonable to have ${ ... } strip newlines and
> "${ ... }" keep them, if that feels better.

The attached patch implements this, for purposes of discussion.  The
doc updates are much larger than the actual code change.

diff --git a/Doc/Zsh/expn.yo b/Doc/Zsh/expn.yo
index 183ca6e03..b77942697 100644
--- a/Doc/Zsh/expn.yo
+++ b/Doc/Zsh/expn.yo
@@ -1950,6 +1950,9 @@ the braces by whitespace, like `tt(${ )...tt( })', is replaced by its
 standard output.  Like `tt(${|)...tt(})' and unlike
 `tt($LPAR())...tt(RPAR())', the command executes in the current shell
 context with function local behaviors and does not create a subshell.
+Word splitting does not apply unless tt(SH_WORD_SPLIT) is set, but
+trailing newlines em(are) stripped unless the substitution is enclosed
+in double quotes.
 
 Note that because the `tt(${|)...tt(})' and `tt(${ )...tt( })' forms
 must be parsed at once as both string tokens and commands, all other
diff --git a/Etc/FAQ.yo b/Etc/FAQ.yo
index 4a86050e6..0515d2fca 100644
--- a/Etc/FAQ.yo
+++ b/Etc/FAQ.yo
@@ -1092,10 +1092,11 @@ sect(Comparisons of forking and non-forking command substitution)
   affects the caller.
 
   mytt($(command)) removes trailing newlines from the output of mytt(command)
-  when substituting, whereas mytt(${ command }) and its variants do not.
-  The latter is consistent with mytt(${|...}) from mksh but differs from
-  bash and ksh, so in emulation modes, newlines are stripped from command
-  output (not from tt(REPLY) assignments).
+  when substituting, as does mytt(${ command }) when not quoted.  Placing
+  double quotes around mytt("${ command }"), or using either mytt(${|...})
+  format, retains newlines.  The latter is consistent with mytt(${|...})
+  from mksh, but mytt("${ command }") differs from bash and ksh, so in
+  emulation modes, newlines stripped even from quoted command output.
 
   When not enclosed in double quotes, the expansion of mytt($(command)) is
   split on tt(IFS) into an array of words.  In contrast, and unlike both
diff --git a/Src/subst.c b/Src/subst.c
index 49f7336bb..785137357 100644
--- a/Src/subst.c
+++ b/Src/subst.c
@@ -2005,7 +2005,7 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags,
 		int onoerrs = noerrs, rplylen;
 		noerrs = 2;
 		rplylen = zstuff(&cmdarg, rplytmp);
-		if (! EMULATION(EMULATE_ZSH)) {
+		if (! EMULATION(EMULATE_ZSH) || !qt) {
 		    /* bash and ksh strip trailing newlines here */
 		    while (rplylen > 0 && cmdarg[rplylen-1] == '\n')
 			rplylen--;
diff --git a/Test/D10nofork.ztst b/Test/D10nofork.ztst
index d6a5588df..1c6a30cb0 100644
--- a/Test/D10nofork.ztst
+++ b/Test/D10nofork.ztst
@@ -159,7 +159,7 @@ F:Why not use this error in the previous case as well?
 1:unbalanced braces, part 4+
 ?(eval):1: closing brace expected
 
-  purr ${ purr STDOUT }
+  purr "${ purr STDOUT }"
 0:capture stdout
 >STDOUT
 >
@@ -322,7 +322,7 @@ F:Fiddly here to get EOF past the test syntax
 0:here-string behavior
 >in a here string
 
-  <<<${ purr $'stdout as a here string' }
+  <<<"${ purr $'stdout as a here string' }"
 0:another capture stdout
 >stdout as a here string
 >
@@ -331,7 +331,7 @@ F:Fiddly here to get EOF past the test syntax
   wrap=${ purr "capture in environment assignment" } typeset -p wrap
 0:assignment context
 >typeset -g wrap='REPLY in environment assignment'
->typeset -g wrap=$'capture in environment assignment\n'
+>typeset -g wrap='capture in environment assignment'
 
 # Repeat return and exit tests with stdout capture
 
@@ -410,7 +410,7 @@ F:must do this before evaluating the next test block
 0:ignored braces, part 1
 >buried}
 
-  purr ${ purr ${REPLY:-buried}}}
+  purr "${ purr ${REPLY:-buried}}}"
 0:ignored braces, part 2
 >buried
 >}
@@ -418,7 +418,6 @@ F:must do this before evaluating the next test block
   purr ${ { echo nested ;} }
 0:ignored braces, part 3
 >nested
->
 
   purr ${ { echo nested } } DONE
 1:ignored braces, part 4