Rewrite the line splitting logic to avoid stack buffers

The new logic reads the source buffer exactly once and
moves the accumulated buffer in the dedicated buffer.

This implementation avoids VLAs and instead uses
a dedicated buffer allocated with xCalloc. The buffer is
guaranteed to be at least 40 characters wide, meaning on narrow
displays horizontal scrolling will be necessary. Doing so ensures
a half-decent chance for arguments to fit fully in one line.

Author: BenBE

CommandScreen.c

@@ -25,23 +25,33 @@ static void CommandScreen_scan(InfoScreen* this) {
    Panel_prune(panel);
 
    const char* p = Process_getCommand(this->process);
-   char line[COLS + 1];
-   int line_offset = 0, last_spc = -1;
-   for (; *p != '\0'; p++, line_offset++) {
-      assert(line_offset >= 0 && (size_t)line_offset < sizeof(line));
-      line[line_offset] = *p;
-      if (*p == ' ') {
-         last_spc = line_offset;
-      }
 
-      if (line_offset == COLS) {
-         int len = last_spc <= 0 ? line_offset : last_spc;
-         line[len] = '\0';
+   size_t line_maxlen = COLS < 40 ? 40 : COLS;
+   size_t line_offset = 0;
+   size_t last_space = 0;
+   char* line = xCalloc(line_maxlen + 1, sizeof(char));
+
+   for (; *p != '\0'; p++) {
+      if (line_offset >= line_maxlen) {
+         assert(line_offset <= line_maxlen);
+         assert(last_space <= line_maxlen);
+
+         size_t line_len = last_space <= 0 ? line_offset : last_space;
+         char tmp = line[line_len];
+         line[line_len] = '\0';
          InfoScreen_addLine(this, line);
+         line[line_len] = tmp;
+
+         assert(line_len <= line_offset);
+         line_offset -= line_len;
+         memmove(line, line + line_len, line_offset);
 
-         line_offset -= len;
-         last_spc = -1;
-         memcpy(line, p - line_offset, line_offset + 1);
+         last_space = 0;
+      }
+
+      line[line_offset++] = *p;
+      if (*p == ' ') {
+         last_space = line_offset;
       }
    }
 
@@ -50,6 +60,8 @@ static void CommandScreen_scan(InfoScreen* this) {
       InfoScreen_addLine(this, line);
    }
 
+   free(line);
+
    Panel_setSelected(panel, idx);
 }