tcsh/tcsh-6.24.10-history-merge.dif

---
 sh.hist.c |   22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

--- sh.hist.c
+++ sh.hist.c	2023-07-13 09:18:13.149624778 +0000
@@ -105,7 +105,7 @@ hremove(struct Hist *hp)
 
 /* Prune length of history list to specified size by history variable. */
 PG_STATIC void
-discardExcess(int hlen)
+discardExcess(int hlen, int mflg)
 {
     struct Hist *hp, *np;
     if (histTail == NULL) {
@@ -116,13 +116,13 @@ discardExcess(int hlen)
      * the list is still too long scan the whole list as before.  But only do a
      * full scan if the list is more than 6% (1/16th) too long. */
     while (histCount > (unsigned)hlen && (np = Histlist.Hnext)) {
-        if (eventno - np->Href >= hlen || hlen == 0)
+        if ((eventno - np->Href >= hlen || hlen == 0) && !mflg)
             hremove(np), hfree(np);
         else
             break;
     }
     while (histCount > (unsigned)hlen && (np = histTail) != &Histlist) {
-        if (eventno - np->Href >= hlen || hlen == 0)
+        if (eventno - np->Href >= hlen || hlen == 0 || mflg)
             hremove(np), hfree(np);
         else
             break;
@@ -148,7 +148,7 @@ savehist(
 	return;
     if (sp)
         (void) enthist(++eventno, sp, 1, mflg, histlen);
-    discardExcess(histlen);
+    discardExcess(histlen, mflg);
 }
 
 #define USE_JENKINS_HASH 1
@@ -1404,6 +1404,18 @@ loadhist(Char *fname, int mflg)
 void
 sethistory(int n)
 {
+    int mflg = 0;
+    struct varent *shist;
+
+    if ((shist = adrof(STRsavehist)) != NULL && shist->vec != NULL) {
+	size_t i;
+	for (i = 1; shist->vec[i]; i++) {
+	    if (eq(shist->vec[i], STRmerge)) {
+		mflg++;
+		break;
+	    }
+	}
+    }
     histlen = n;
-    discardExcess(histlen);
+    discardExcess(histlen, mflg);
 }