Xic/WRspice/Mozy: fixes to avoid seg faults from gcc-8.2 (Fedora 29).

This compiler seg faults when a method is called on a null object.
Once upon a time this was perfectly fine, and one could test the
'this' pointer in the called function for a null object.  Xic and
WRspice used this "feature" a lot, and have had to be updated as a
consequence.  Somehow two instances of un-updated code didn't fault
until this compiler.

mozy/include/help/help_topic.h

@@ -51,7 +51,7 @@ struct HLPtopList
 {
     HLPtopList(const char *d, const char *kw, HLPtopic *t, HLPtopList *n)
         {
-            next = n;
+            tl_next = n;
             tl_keyword = lstring::copy(kw);
             tl_description = lstring::copy(d);
             tl_buttontext = 0;
@@ -66,18 +66,26 @@ struct HLPtopList
             delete [] tl_description;
         }
 
+    HLPtopList *next()          { return (tl_next); }
+    const char *keyword()       const { return (tl_keyword); }
+    const char *description()   const { return (tl_description); }
+    const char *buttontext()    const { return (tl_buttontext); }
+
+    void set_buttontext(const char *t)  { tl_buttontext = t; }
+
     static void destroy(HLPtopList *tl)
         {
             while (tl) {
                 HLPtopList *tx = tl;
-                tl = tl->next;
+                tl = tl->tl_next;
                 delete tx;
             }
         }
 
-    HLPtopList *sort();
+    static HLPtopList *sort(HLPtopList*);
 
-    HLPtopList *next;
+private:
+    HLPtopList *tl_next;
     char *tl_keyword;
     char *tl_description;
     const char *tl_buttontext;
@@ -196,12 +204,14 @@ struct HLPtopic
     HLPtopList *subtopics()     { return (tp_subtopics); }
     void add_subtopic(const char *t, const char *w)
         { tp_subtopics = new HLPtopList(t, w, this, tp_subtopics); }
-    void sort_subtopics()       { tp_subtopics = tp_subtopics->sort(); }
+    void sort_subtopics()
+        { tp_subtopics = HLPtopList::sort(tp_subtopics); }
 
     HLPtopList *seealso()       { return (tp_seealso); }
     void add_seealso(const char *t, const char *w)
         { tp_seealso = new HLPtopList(t, w, this, tp_seealso); }
-    void sort_seealso()         { tp_seealso = tp_seealso->sort(); }
+    void sort_seealso()
+        { tp_seealso = HLPtopList::sort(tp_seealso); }
 
     GRwbag *context()           { return (tp_context); }
     void set_context(GRwbag *c) { tp_context = c; }

mozy/src/help/help_read.cc

@@ -555,7 +555,7 @@ cHelp::search(const char *target)
     top->sort_seealso();
     int i;
     HLPtopList *tl;
-    for (i = 0, tl = top->seealso(); tl; i++, tl = tl->next) ;
+    for (i = 0, tl = top->seealso(); tl; i++, tl = tl->next()) ;
     sprintf(buf, "Keyword search for %s : %d entries found.", target, i);
     top->set_words(new HLPwords(buf, 0));
     top->register_word(buf);

mozy/src/help/help_topic.cc

@@ -492,23 +492,23 @@ HLPtopic::load_text()
     if (!tp_show_plain) {
         if (tp_subtopics) {
             lstr.add("<H3>Subtopics</H3>\n");
-            for (HLPtopList *tl = tp_subtopics; tl; tl = tl->next) {
-                tl->tl_buttontext = tl->tl_description;
-                if (!tl->tl_buttontext)
-                    tl->tl_buttontext = "<unknown>";
+            for (HLPtopList *tl = tp_subtopics; tl; tl = tl->next()) {
+                tl->set_buttontext(tl->description());
+                if (!tl->buttontext())
+                    tl->set_buttontext("<unknown>");
                 sprintf(tbuf, "<A HREF=\"%s\">%s</A><BR>\n",
-                    tl->tl_keyword, tl->tl_buttontext);
+                    tl->keyword(), tl->buttontext());
                 lstr.add(tbuf);
             }
         }
         if (tp_seealso) {
             lstr.add("<H3>References</H3>\n");
-            for (HLPtopList *tl = tp_seealso; tl; tl = tl->next) {
-                tl->tl_buttontext = tl->tl_description;
-                if (!tl->tl_buttontext)
-                    tl->tl_buttontext = "<unknown>";
+            for (HLPtopList *tl = tp_seealso; tl; tl = tl->next()) {
+                tl->set_buttontext(tl->description());
+                if (!tl->buttontext())
+                    tl->set_buttontext("<unknown>");
                 sprintf(tbuf, "<A HREF=\"%s\">%s</A><BR>\n",
-                    tl->tl_keyword, tl->tl_buttontext);
+                    tl->keyword(), tl->buttontext());
                 lstr.add(tbuf);
             }
         }
@@ -558,11 +558,11 @@ namespace {
     // Strip HTML tags from the beginning of the string, return the first
     // text.
     //
-    inline char *
-    striptag(char *s)
+    inline const char *
+    striptag(const char *s)
     {
         while (*s == '<') {
-            char *t = s + 1;
+            const char *t = s + 1;
             while (*t && *t != '>')
                 t++;
             if (!*t)
@@ -575,8 +575,8 @@ namespace {
     inline bool
     sortcmp(const HLPtopList *tlp1, const HLPtopList *tlp2)
     {
-        char *s1 = tlp1->tl_description;
-        char *s2 = tlp2->tl_description;
+        const char *s1 = tlp1->description();
+        const char *s2 = tlp2->description();
         s1 = striptag(s1);
         s2 = striptag(s2);
         while (*s1 && *s2) {
@@ -606,23 +606,23 @@ namespace {
 
 
 HLPtopList *
-HLPtopList::sort()
+HLPtopList::sort(HLPtopList *list)
 {
-    int num;
     HLPtopList *tl;
-    for (num = 0, tl = this; tl; num++, tl = tl->next) ;
+    int num;
+    for (tl = list, num = 0; tl; num++, tl = tl->tl_next) ;
     if (num < 2)
-        return (this);
+        return (list);
 
     HLPtopList **vec = new HLPtopList*[num];
     int i;
-    for (tl = this, i = 0; tl; tl = tl->next, i++)
+    for (tl = list, i = 0; tl; tl = tl->tl_next, i++)
         vec[i] = tl;
     std::sort(vec, vec + num, sortcmp);
     tl = vec[0];
     for (i = 0; i < num - 1; i++)
-        vec[i]->next = vec[i + 1];
-    vec[i]->next = 0;
+        vec[i]->tl_next = vec[i + 1];
+    vec[i]->tl_next = 0;
     delete [] vec;
     return (tl);
 }

xic/include/pushpop.h

@@ -84,7 +84,7 @@ struct ContextDesc
 
     void purge(const CDs*, const CDl*);
     ContextDesc *purge(const CDs*, const CDo*);
-    void clear();
+    static void clear(ContextDesc*);
 
     int level()
         {
@@ -119,8 +119,8 @@ struct CXstate
 
     ~CXstate()
         {
-            context->clear();
-            context_history->clear();
+            ContextDesc::clear(context);
+            ContextDesc::clear(context_history);
         }
 
     CDcellName cellname;

xic/src/main/pushpop.cc

@@ -113,7 +113,7 @@ ContextDesc::purge(const CDs *sd, const CDo *od)
                 cp->cNext = 0;
             else
                 c0 = 0;
-            cx->clear();
+            ContextDesc::clear(cx);
             return (c0);
         }
         if (cx->cState)
@@ -124,10 +124,10 @@ ContextDesc::purge(const CDs *sd, const CDo *od)
 }
 
 
+// Static function.
 void
-ContextDesc::clear()
+ContextDesc::clear(ContextDesc *c)
 {
-    ContextDesc *c = this;
     while (c) {
         ContextDesc *cn = c->cNext;
         delete c;
@@ -280,7 +280,7 @@ cPushPop::PushContext(const CDc *cdesc, unsigned int xind, unsigned int yind)
         msdesc = cdesc->masterCell();
         if (!msdesc)
             return;
-        context_history->clear();  // clear history
+        ContextDesc::clear(context_history);  // clear history
         context_history = 0;
         context = new ContextDesc(cdesc, xind, yind);
 
@@ -434,7 +434,7 @@ cPushPop::ClearContext(bool skip_commit)
     while (context)
         PopContext();
     no_display = false;
-    context_history->clear();
+    ContextDesc::clear(context_history);
     context_history = 0;
     if (!skip_commit)
         XM()->CommitCell();
@@ -452,9 +452,9 @@ cPushPop::ClearContext(bool skip_commit)
 void
 cPushPop::ClearLists()
 {
-    context->clear();
+    ContextDesc::clear(context);
     context = 0;
-    context_history->clear();
+    ContextDesc::clear(context_history);
     context_history = 0;
 }
 
@@ -490,9 +490,9 @@ cPushPop::PopState()
 void
 cPushPop::PushState(CXstate *ecx)
 {
-    context->clear();
+    ContextDesc::clear(context);
     context = 0;
-    context_history->clear();
+    ContextDesc::clear(context_history);
     context_history = 0;
 
     if (ecx) {