helpful

commit b97947b2033e33eb5fddb71ec840a3221b27e87c
parent c87f865c7a3c15ed0c049099694ee6cc4643b684
Author: Wilfred Hughes <me@wilfred.me.uk>
Date:   Thu, 10 May 2018 08:42:18 +0100

Don't highlight very large code snippets

This stops big code excerpts hanging Emacs when using helpful.
Fixes #107.

Diffstat:
M
CHANGELOG.md
 | 
4
++++
M
helpful.el
 | 
47
++++++++++++++++++++++++++++-------------------

2 files changed, 32 insertions(+), 19 deletions(-)
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -14,6 +14,10 @@ Function signatures are now correct when a function uses
 Fixed an issue where escaped backticks were confused with unescaped
 backticks in docstrings.
 
+Fixed an issue with very large code snippets making helpful hang due
+to slow syntax highlighting. This was particularly problematic for C
+functions and variables.
+
 # v0.9
 
 Much better handling of aliases: show aliases differently to their
diff --git a/helpful.el b/helpful.el
@@ -82,6 +82,14 @@ To disable cleanup entirely, set this variable to nil. See also
   :type 'function
   :group 'helpful)
 
+;; TODO: explore whether more basic highlighting is fast enough to
+;; handle larger functions. See `c-font-lock-init' and its use of
+;; font-lock-keywords-1.
+(defconst helpful-max-highlight 5000
+  "Don't highlight code with more than this many characters.
+This is particularly important for large pieces of C code, such
+as describing `this-command'.")
+
 (defun helpful--kind-name (symbol callable-p)
   "Describe what kind of symbol this is."
   (cond
@@ -905,25 +913,26 @@ hooks.")
   (with-temp-buffer
     (insert source)
 
-    ;; Switch to major-mode MODE, but don't run any hooks.
-    (delay-mode-hooks (funcall mode))
-
-    ;; `delayed-mode-hooks' contains mode hooks like
-    ;; `emacs-lisp-mode-hook'. Build a list of functions that are run
-    ;; when the mode hooks run.
-    (let (hook-funcs)
-      (dolist (hook delayed-mode-hooks)
-        (let ((funcs (symbol-value hook)))
-          (setq hook-funcs (append hook-funcs funcs))))
-
-      ;; Filter hooks to those that relate to highlighting, and run them.
-      (setq hook-funcs (-intersection hook-funcs helpful--highlighting-funcs))
-      (-map #'funcall hook-funcs))
-
-    (if (fboundp 'font-lock-ensure)
-        (font-lock-ensure)
-      (with-no-warnings
-        (font-lock-fontify-buffer)))
+    (when (< (length source) helpful-max-highlight)
+      ;; Switch to major-mode MODE, but don't run any hooks.
+      (delay-mode-hooks (funcall mode))
+
+      ;; `delayed-mode-hooks' contains mode hooks like
+      ;; `emacs-lisp-mode-hook'. Build a list of functions that are run
+      ;; when the mode hooks run.
+      (let (hook-funcs)
+        (dolist (hook delayed-mode-hooks)
+          (let ((funcs (symbol-value hook)))
+            (setq hook-funcs (append hook-funcs funcs))))
+
+        ;; Filter hooks to those that relate to highlighting, and run them.
+        (setq hook-funcs (-intersection hook-funcs helpful--highlighting-funcs))
+        (-map #'funcall hook-funcs))
+
+      (if (fboundp 'font-lock-ensure)
+          (font-lock-ensure)
+        (with-no-warnings
+          (font-lock-fontify-buffer))))
     (buffer-string)))
 
 (defun helpful--source (sym callable-p)