Add empty-body warning for when, unless etc

Warn about code like (when SOME-CONDITION) because these may indicate
bugs.  Warnings currently apply to `when`, `unless`, `ignore-error`,
`with-suppressed-warnings` and (as before) `let` and `let*`.

* lisp/emacs-lisp/byte-run.el (with-suppressed-warnings):
Update doc string.
* lisp/emacs-lisp/bytecomp.el: (byte-compile-warning-types)
(byte-compile-warnings): Add empty-body.
(byte-compile-initial-macro-environment):
Add empty-body warning for with-suppressed-warnings.
* lisp/emacs-lisp/macroexp.el (macroexp--expand-all):
Use the empty-body category for let and let*.
* lisp/subr.el (when, unless, ignore-error): Add empty-body warning.
* test/lisp/emacs-lisp/bytecomp-tests.el
(bytecomp-test--with-suppressed-warnings): Add test cases.

1 files changed, 44 insertions, 1 deletions

diff --git a/test/lisp/emacs-lisp/bytecomp-tests.el b/test/lisp/emacs-lisp/bytecomp-tests.el
index 61f4998f6ba..eec66c9585a 100644
--- a/test/lisp/emacs-lisp/bytecomp-tests.el
+++ b/test/lisp/emacs-lisp/bytecomp-tests.el
@@ -1433,7 +1433,50 @@ literals (Bug#20852)."
         (set-buffer (get-buffer-create "foo"))
         nil))
    '((suspicious set-buffer))
-   "Warning: Use .with-current-buffer. rather than"))
+   "Warning: Use .with-current-buffer. rather than")
+
+  (test-suppression
+   '(defun zot ()
+      (let ((_ 1))
+        ))
+   '((empty-body let))
+   "Warning: Empty let body")
+
+  (test-suppression
+   '(defun zot ()
+      (let* ((_ 1))
+        ))
+   '((empty-body let*))
+   "Warning: Empty let\\* body")
+
+  (test-suppression
+   '(defun zot (x)
+      (when x
+        ))
+   '((empty-body when))
+   "Warning: `when' with empty body")
+
+  (test-suppression
+   '(defun zot (x)
+      (unless x
+        ))
+   '((empty-body unless))
+   "Warning: `unless' with empty body")
+
+  (test-suppression
+   '(defun zot (x)
+      (ignore-error arith-error
+        ))
+   '((empty-body ignore-error))
+   "Warning: `ignore-error' with empty body")
+
+  (test-suppression
+   '(defun zot (x)
+      (with-suppressed-warnings ((suspicious eq))
+        ))
+   '((empty-body with-suppressed-warnings))
+   "Warning: `with-suppressed-warnings' with empty body")
+  )
 
 (ert-deftest bytecomp-tests--not-writable-directory ()
   "Test that byte compilation works if the output directory isn't