Fix issue #7352

The string assignment function (really in reinitString) wasn't setting the null
terminator at the end of a string in certain cases.

The included new test demonstrates the previous bug and now passes.

Author: mppf

modules/internal/String.chpl

@@ -262,19 +262,20 @@ module String {
             const allocSize = chpl_here_good_alloc_size(s_len+1);
             this.buff = chpl_here_alloc(allocSize,
                                        CHPL_RT_MD_STR_COPY_DATA):bufferType;
-            this.buff[s_len] = 0;
             this._size = allocSize;
             // We just allocated a buffer, make sure to free it later
             this.owned = true;
           }
           c_memmove(this.buff, buf, s_len);
+          this.buff[s_len] = 0;
         } else {
           if this.owned && !this.isEmptyString() then
             chpl_here_free(this.buff);
           this.buff = buf;
           this._size = size;
         }
       } else {
+        // s_len == 0 so the source string is empty
         // free the old buffer
         if this.owned && !this.isEmptyString() then chpl_here_free(this.buff);
         this.buff = nil;

test/types/string/ferguson/null-terminate-assign.chpl

@@ -0,0 +1,9 @@
+extern proc printf(fmt:c_string, arg:c_string);
+
+var s1 = "0" * 10;
+var s2 = "1" * 3;
+
+var test = s1;
+test = s2;
+
+printf("%s\n", test.c_str());

test/types/string/ferguson/null-terminate-assign.good

@@ -0,0 +1 @@
+111