Set $status after while depending on whether loop was entered

Closes #4982.

CHANGELOG.md

@@ -69,6 +69,7 @@ fish 3.0 is a major release which brings with it both improvements in functional
 - Autosuggestions try to avoid arguments that are already present in the command line.
 - Variables may be used inside commands (#154).
 - A `hash` function has been added for compatibiility with `sh` and `bash`
+- `while` sets `$status` to a more useful value (#4982)
 
 ## Other significant changes
 - Command substitution output is now limited to 10 MB by default (#3822).

src/parse_execution.cpp

@@ -528,6 +528,7 @@ parse_execution_result_t parse_execution_context_t::run_while_statement(
     tnode_t<g::andor_job_list> condition_boolean_tail = header.child<3>();
 
     // Run while the condition is true.
+    bool loop_executed = false;
     for (;;) {
         // Check the condition.
         parse_execution_result_t cond_ret =
@@ -547,6 +548,8 @@ parse_execution_result_t parse_execution_context_t::run_while_statement(
             break;
         }
 
+        loop_executed = true;
+
         // Push a while block and then check its cancellation reason.
         while_block_t *wb = parser->push_block<while_block_t>();
         this->run_job_list(contents, wb);
@@ -569,6 +572,11 @@ parse_execution_result_t parse_execution_context_t::run_while_statement(
             break;
         }
     }
+
+    if (loop_executed) {
+        proc_set_last_status(STATUS_CMD_OK);
+    }
+
     return ret;
 }