Fix syntax error assertion failure (fix #3348) (#3350)

src/locfile.c

@@ -78,8 +78,7 @@ void locfile_locate(struct locfile* l, location loc, const char* fmt, ...) {
 
   int startline = locfile_get_line(l, loc.start);
   int offset = l->linemap[startline];
-  int end = MIN(loc.end, l->linemap[startline+1] - 1);
-  assert(end > loc.start);
+  int end = MIN(loc.end, MAX(l->linemap[startline+1] - 1, loc.start + 1));
   jv underline = jv_string_repeat(jv_string("^"), end - loc.start);
   jv m2 = jv_string_fmt("%s at %s, line %d, column %d:\n    %.*s\n    %*s",
                         jv_string_value(m1), jv_string_value(l->fname),

tests/shtest

@@ -711,6 +711,20 @@ jq: 3 compile errors
 EOF
 diff $d/out $d/expected
 
+# Test syntax error messages when error happens at the end.
+if $VALGRIND $Q $JQ -n 'if
+' > $d/out 2>&1; then
+  echo 'syntax error not detected'
+  exit 1
+fi
+cat > $d/expected <<EOF
+jq: error: syntax error, unexpected end of file at <top-level>, line 1, column 3:
+    if
+      ^
+jq: 1 compile error
+EOF
+diff $d/out $d/expected
+
 # Comments!
 if ! x=$($JQ -n '123 # comment') || [ "$x" != 123 ]; then
   echo 'comment did not work'