Re: [PATCH] Support the mksh's ${|func;} substitution

[Sebastian Gniazdowski <sgniazdowski@gmail.com>]

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Hi,
I was looking at some of my old patches and stumbled upon this one
which implements mksh' ${|func;} substitution. The old thread went
over a complex (x) flag choice as a expected candidate for such use
case, however I've now thought that something is better than nothing
and that implementing simpler ${!func;} doesn't block us from adding a
more advanced x-flag in the future. Also, the simplicity of this
substitution is a plus for it, opposed to x-flag complexity (think of
existing e flag, whose's use is fairly complex).

So I thought that I send the patch again upon cleaning conflicts, for
consideration. Or should we revive the advanced x-flag?

To recall - the ${|func;} substitution runs function "func" and
substitutes (returned string in…) $REPLY after it has completed,
without (!) doing forks, which is a performance and functionality
benefit over currently available equivalent: $(func;print -rn --
$REPLY). Original thread:
https://zsh.org/mla/workers/2019/msg00768.html

-- 
Best regards,
Sebastian Gniazdowski

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From 5129820336782902f0dc43d7f196bb66c4579fb9 Mon Sep 17 00:00:00 2001
From: Sebastian Gniazdowski <sgniazdowski@gmail.com>
Date: Wed, 3 May 2023 14:47:01 +0059
Subject: Support the mksh's ${|func;} substitution

---
 Src/subst.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 50 insertions(+), 1 deletion(-)

diff --git a/Src/subst.c b/Src/subst.c
index 974d6171e..abb458195 100644
--- a/Src/subst.c
+++ b/Src/subst.c
@@ -29,6 +29,7 @@
 
 #include "zsh.mdh"
 #include "subst.pro"
+#include "exec.pro"
 
 #define LF_ARRAY	1
 
@@ -1860,8 +1861,17 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags,
      * joining the array into a string (for compatibility with ksh/bash).
      */
     int quoted_array_with_offset = 0;
+    /* Indicates ${|func;} */
+    int rplyfunc = 0;
+    /* The name of the function to be ran by ${|...;} */
+    char *cmdarg = NULL;
+    /* The length of the input string */
+    int slen = 0;
+    /* The closing brace pointer */
+    char *outbracep;
 
     *s++ = '\0';
+    slen = strlen(s);
     /*
      * Nothing to do unless the character following the $ is
      * something we recognise.
@@ -1889,6 +1899,41 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags,
     if (c == Inbrace) {
 	inbrace = 1;
 	s++;
+
+        /* Short-path for the function-running substitution ${|func;}
+         * The function name is extracted and called, and the
+         * substitution assigned. There's no (...)-flags processing,
+         * i.e. no ${|(U)func;}, because it looks quite awful and
+         * also requires a change to the manual, part about the
+         * substitution order. Use ${(U)${|func;}} instead, it looks
+         * cleaner. */
+        if ( ((outbracep=strchr(s,Outbrace)) ||
+             (outbracep=strchr(s,'}'))) &&
+                (s[0] == Bar || s[0] == '|') &&
+                    outbracep[-1] == ';' )
+        {
+            rplyfunc = 1;
+            cmdarg = dupstrpfx(s+1, outbracep-s-2);
+            s=outbracep;
+
+            HashNode hn = NULL;
+            if( (hn = shfunctab->getnode(shfunctab, cmdarg)) ) {
+                /* Execute the shell function */
+                doshfunc((Shfunc) hn, NULL, 1);
+                val = getsparam("REPLY");
+                if (val)
+                    vunset = 0;
+                else {
+                    vunset = 1;
+                    val = dupstring("");
+            }
+        } else {
+                zerr("no such function: %s", cmdarg);
+                return NULL;
+        }
+            fetch_needed = 0;
+    }
+
 	/*
 	 * In ksh emulation a leading `!' is a special flag working
 	 * sort of like our (k).  This is true only for arrays or
@@ -2589,7 +2634,11 @@ paramsubst(LinkList l, LinkNode n, char **str, int qt, int pf_flags,
 			     scanflags)) ||
 	    (v->pm && (v->pm->node.flags & PM_UNSET)) ||
 	    (v->flags & VALFLAG_EMPTY))
-	    vunset = 1;
+        {
+            if (!rplyfunc) {
+                vunset = 1;
+        }
+    }
 
 	if (wantt) {
 	    /*
-- 
2.28.0