问题
之前一直使用evil-collection包以完善evil-mode绑定在各个地方的一致性及覆盖率，特别的，evil-collection会为pdf-tools创建对应的evil-mode绑定，比如 / 和 ? 会绑定到 isearch-forward/isearch-backward 上，
n/N 则会绑定到 isearch-repeat-forward/isearch-repeat-backward 上，问题在于pdf-tools的整个搜索机制是基于isearch上实现的，故很多行为和isearch一致，但是和evil-mode用户的期望却不匹配，比如：
- 按
C-s 开始isearch搜索，然后输入关键字，此时默认匹配项会渐进高亮，这个没问题，问题是按回车后，isearch认为搜索结束，会直接清除高亮，这个行为可以通过 lazy-highlight-cleanup
来控制，问题是，pdf-tools直接禁用了isearch的lazy-highlight机制，导致 lazy-highlight-cleanup 无法控制该行为。由于按 / 也是调用
isearch-forward 进行搜索，因此在输入关键字后按回车，高亮一样会消失，这和平常evil-mode的行为是不一致的。
- 按
/ 开始搜索，输入关键字，之后按回车后， isearch-mode 会被禁用，这之后按 n/N 调用 isearch-repeat-forward/isearch-repeat-backward
会进一步跳转到下一个匹配项，这点和预期一样，但是当搜索到PDF文件的下一页时，高亮会消失，出现该问题是因为，在搜索当前页时，pdf-tools不会redisplay
该页的内容，但是当搜索进行到PDF文件的下一页后，pdf-tools会进行redisplay，此时检测到 isearch-mode 没有启用，便不会进行高亮了。
- 绑定到
n/N 的命令 isearch-repeat-forward/isearch-repeat-backward
不会记住上一次的搜索方向。
思路及解决方案
我在Emacs China中发过完整的解决方案，这里主要讲下思路。
先解决在 / 搜索后，按回车，高亮会消失的问题，回答一个问题：为什么按回车后高亮会被清除？答案在于 pdf-isearch-mode-cleanup 函数，代码如下：
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(defun pdf-isearch-mode-cleanup ()
"Cleanup after exiting Isearch.
This is a Isearch interface function."
(pdf-isearch-active-mode -1)
(pdf-view-redisplay))
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该函数调用 pdf-view-redisplay 以redisplay当前页面，这时候高亮就没了。该函数会在 isearch-mode-end-hook 的时候被执行，如下：
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(add-hook 'isearch-mode-end-hook 'pdf-isearch-mode-cleanup nil t)
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而 isearch-mode-end-hook 会在isearch搜索结束后被触发，也就是按回车后的时候触发，这就是为什么按回车后，高亮会消失。我们期望的行为是：搜索如果匹配失败了，则回车后清除高亮，否则，回车后保持高亮，最简单、但是比较hack的方式就是覆盖 pdf-isearch-mode-cleanup 的实现，为此，我们先定义一个函数来判断isearch是否搜索匹配失败，如下：
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(defun osfva-isearch-failed? ()
(or (not isearch-success) isearch-error))
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接着，我们用advice覆盖 pdf-isearch-mode-cleanup 的实现，仅在搜索失败的时候，清除高亮，如下：
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(defun osfva-pdf-isearch-mode-cleanup ()
"Don't cleanup highlight if search successfully."
(pdf-isearch-active-mode -1)
(when (osfva-isearch-failed?) (pdf-view-redisplay)))
(advice-add #'pdf-isearch-mode-cleanup
:override #'osfva-pdf-isearch-mode-cleanup)
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解决完回车后清除高亮的问题后，我们继续解决第二个问题，即按 n/N 在搜索进行到下一页后，高亮会消失的问题，造成这个问题的原因是
pdf-isearch-hl-matches ，它的实现如下：
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(defun pdf-isearch-hl-matches (current matches &optional occur-hack-p)
"Highlighting edges CURRENT and MATCHES."
(cl-check-type current pdf-isearch-match)
(cl-check-type matches (list-of pdf-isearch-match))
(cl-destructuring-bind (fg1 bg1 fg2 bg2)
(pdf-isearch-current-colors)
(let* ((width (car (pdf-view-image-size)))
(page (pdf-view-current-page))
(window (selected-window))
(buffer (current-buffer))
(tick (cl-incf pdf-isearch--hl-matches-tick))
(pdf-info-asynchronous
(lambda (status data)
(when (and (null status)
(eq tick pdf-isearch--hl-matches-tick)
(buffer-live-p buffer)
(window-live-p window)
(eq (window-buffer window)
buffer))
(with-selected-window window
(when (and (derived-mode-p 'pdf-view-mode)
(or isearch-mode
occur-hack-p)
(eq page (pdf-view-current-page)))
(pdf-view-display-image
(pdf-view-create-image data :width width))))))))
(pdf-info-renderpage-text-regions
page width t nil
`(,fg1 ,bg1 ,@(pdf-util-scale-pixel-to-relative
current))
`(,fg2 ,bg2 ,@(pdf-util-scale-pixel-to-relative
(apply 'append
(remove current matches))))))))
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重点看那个lambda里面的内容，这个lambda会在 pdf-info-renderpage-text-regions 渲染完成后，异步执行，由于渲染是异步做的，因此渲染完成后，我们的PDF缓冲区、窗口可能已经被kill或者
delete掉了，甚至major-mode等被改变了，故它在lambda中做了一系列检查，比如 (buffer-live-p buffer) 、 (window-live-p window) 、
(derived-mode-p 'pdf-view-mode) 等等，检查通过才进行高亮，特别重要的一个就是，它检查了 isearch-mode 是否处于启用状态，然而前面说了，回车后， isearch-mode 会被禁用，故该判断会失败，不过注意到它还判断参数
occur-hack-p 是否为真，如果为真，则即使 isearch-mode 处于禁用状态时也进行高亮，那这个 occur-hack-p 是做什么的？这个参数实际上是供
pdf-isearch-occur 命令使用的，该命令可以在 C-s 或者 / 开始搜索后，输入关键字，然后不要按回车，按 M-s o 触发，它用 occur 以进行搜索和显示，会有一个专门的缓冲区列出PDF文件中所有匹配关键字的位置（整个文件，不止当前页），你可以在该缓冲区对应项按回车以跳转到对应页的对应位置，不仅如此，整个过程中当前页面的匹配项都是处于高亮状态的，这个
pdf-isearch-occur 会间接传递 occur-hack-p 为 t 给
pdf-isearch-hl-matches ，从而实现即使 isearch-mode 处于禁用状态时也显示高亮，那我们可以模仿它，注入一个变量以控制高亮的显示，如下：
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(defvar-local osfva-pdf-isearch-highlight-matches nil)
(defun osfva-pdf-isearch-hl-matches-controllable-highlight (orig-fun current matches &optional occur-hack-p)
(funcall orig-fun current matches (or osfva-pdf-isearch-highlight-matches occur-hack-p)))
(advice-add #'pdf-isearch-hl-matches
:around #'osfva-pdf-isearch-hl-matches-controllable-highlight)
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接着，我们创建自己的 isearch-repeat-forward/isearch-repeat-backward ，不同于原函数，我们的函数会设置 osfva-pdf-isearch-hl-matches-controllable-highlight 为non-nil以保证 isearch-mode 处于禁用状态时也显示高亮，如下：
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(defun osfva-pdf-isearch-repeat-forward (&optional arg)
(interactive "P")
(setq osfva-pdf-isearch-highlight-matches t)
(isearch-repeat-forward arg))
(defun osfva-pdf-isearch-repeat-backward (&optional arg)
(interactive "P")
(setq osfva-pdf-isearch-highlight-matches t)
(isearch-repeat-backward arg))
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最后，我们绑定这两个函数到 n/N 键，如下：
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(evil-define-key* 'normal pdf-view-mode-map
(kbd "n") #'osfva-pdf-isearch-repeat-forward
(kbd "N") #'osfva-pdf-isearch-repeat-backward)
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至此，就实现了按 n/N 保持高亮了，但是在搜索过程中，我们会发现一个问题，正常搜索超过PDF结尾时，isearch会暂停，再按一下搜索才会wrap到PDF开头重新开始搜索，这里的问题是，暂停的时候，结尾的高亮会不见，要再按一下搜索，使其wrap到PDF开头高亮才会再次正常显示，一个简单的修复方法就是改成搜索超过PDF结尾时，直接wrap到PDF开头开始搜索，不要暂停，如下：
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(add-hook 'pdf-view-mode-hook
(lambda () (setq-local isearch-wrap-pause 'no)))
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为了避免 osfva-pdf-isearch-hl-matches-controllable-highlight 对正常使用isearch进行搜索产生影响，我们要在pdf-tools正常使用isearch进行搜索时，重置该变量，如下：
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(advice-add #'pdf-isearch-mode-initialize
:before
(lambda (&rest args)
"Reset `osfva-pdf-isearch-highlight-matches'."
(setq osfva-pdf-isearch-highlight-matches nil)))
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针对 pdf-isearch-occur 也可以进行类似的处理，不过读者思考下，会发现
osfva-pdf-isearch-hl-matches-controllable-highlight 的具体值和 pdf-isearch-occur 间接传递 occur-hack-p 为 t
给 pdf-isearch-hl-matches 并不冲突，所以可以不处理。
除此之外，我们还得考虑清除高亮的问题，因为高亮一直都在，我们希望按某个键可以清除高亮，比如 ESC 就是一个合适的选择，先定义清除高亮的函数，如下：
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(defun osfva-pdf-isearch-cleanup-highlight ()
(setq osfva-pdf-isearch-highlight-matches nil)
(pdf-view-redisplay))
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就是调用 pdf-view-redisplay redisplay下，高亮就清除了，还得把 osfva-pdf-isearch-highlight-matches 重置了。
接下来定义另外一个函数，该函数用于替代原始 ESC 的功能，原始 ESC 是进入evil normal state，现在我们替换成进入evil normal state的同时，清除高亮，如下：
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(evil-define-command osfva-pdf-view-force-normal-state ()
:repeat abort
:suppress-operator t
(evil-normal-state)
(osfva-pdf-isearch-cleanup-highlight))
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将该函数绑定到 ESC 上，和之前的绑定一起写，如下：
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(evil-define-key* 'normal pdf-view-mode-map
(kbd "n") #'osfva-pdf-isearch-repeat-forward
(kbd "N") #'osfva-pdf-isearch-repeat-backward
(kbd "<escape>") #'osfva-pdf-view-force-normal-state)
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继续解决下一个问题，即绑定到 n/N 的命令 isearch-repeat-forward/isearch-repeat-backward
不会记住上一次的搜索方向，定义我们自己的搜索函数，让它们记住上一次的搜索方向，如下：
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(defvar-local osfva-pdf-isearch-forward? t)
(defun osfva-pdf-isearch-forward (&optional regexp-p no-recursive-edit)
"Like `isearch-forward', but remember the previous search direction."
(interactive "P\np")
(setq osfva-pdf-isearch-forward? t)
(isearch-forward regexp-p no-recursive-edit))
(defun osfva-pdf-isearch-backward (&optional regexp-p no-recursive-edit)
"Like `isearch-backward', but remember the previous search direction."
(interactive "P\np")
(setq osfva-pdf-isearch-forward? nil)
(isearch-backward regexp-p no-recursive-edit))
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接下来，修改之前定义的 osfva-pdf-isearch-repeat-forward 以及 osfva-pdf-isearch-repeat-backward ，让它们根据记住的搜索方向，自己选择合适方向的搜索函数，如下：
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(defun osfva-pdf-isearch-repeat-forward (&optional arg)
(interactive "P")
(setq osfva-pdf-isearch-highlight-matches t)
(if osfva-pdf-isearch-forward?
(isearch-repeat-forward arg)
(isearch-repeat-backward arg)))
(defun osfva-pdf-isearch-repeat-backward (&optional arg)
(interactive "P")
(setq osfva-pdf-isearch-highlight-matches t)
(if osfva-pdf-isearch-forward?
(isearch-repeat-backward arg)
(isearch-repeat-forward arg)))
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将新的搜索函数绑定到 / 和 ? 上，和之前的绑定一起写，如下：
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(evil-define-key* 'normal pdf-view-mode-map
(kbd "/") #'osfva-pdf-isearch-forward
(kbd "?") #'osfva-pdf-isearch-backward
(kbd "n") #'osfva-pdf-isearch-repeat-forward
(kbd "N") #'osfva-pdf-isearch-repeat-backward
(kbd "<escape>") #'osfva-pdf-view-force-normal-state)
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至此，所有想要的功能都完成了，完整代码如下（外层得用
with-eval-after-load 包裹住，否则一些函数可能未定义，也可以放
use-package的 :config 区域）：
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(with-eval-after-load 'pdf-tools
(defun osfva-isearch-failed? ()
(or (not isearch-success) isearch-error))
(defvar-local osfva-pdf-isearch-highlight-matches nil)
(defun osfva-pdf-isearch-cleanup-highlight ()
(setq osfva-pdf-isearch-highlight-matches nil)
(pdf-view-redisplay))
(defun osfva-pdf-isearch-hl-matches-controllable-highlight (orig-fun current matches &optional occur-hack-p)
(funcall orig-fun current matches (or osfva-pdf-isearch-highlight-matches occur-hack-p)))
(advice-add #'pdf-isearch-hl-matches
:around #'osfva-pdf-isearch-hl-matches-controllable-highlight)
(defvar-local osfva-pdf-isearch-forward? t)
(defun osfva-pdf-isearch-forward (&optional regexp-p no-recursive-edit)
"Like `isearch-forward', but remember the previous search direction."
(interactive "P\np")
(setq osfva-pdf-isearch-forward? t)
(isearch-forward regexp-p no-recursive-edit))
(defun osfva-pdf-isearch-backward (&optional regexp-p no-recursive-edit)
"Like `isearch-backward', but remember the previous search direction."
(interactive "P\np")
(setq osfva-pdf-isearch-forward? nil)
(isearch-backward regexp-p no-recursive-edit))
(defun osfva-pdf-isearch-repeat-forward (&optional arg)
(interactive "P")
(setq osfva-pdf-isearch-highlight-matches t)
(if osfva-pdf-isearch-forward?
(isearch-repeat-forward arg)
(isearch-repeat-backward arg)))
(defun osfva-pdf-isearch-repeat-backward (&optional arg)
(interactive "P")
(setq osfva-pdf-isearch-highlight-matches t)
(if osfva-pdf-isearch-forward?
(isearch-repeat-backward arg)
(isearch-repeat-forward arg)))
(add-hook 'pdf-view-mode-hook
(lambda () (setq-local isearch-wrap-pause 'no)))
(evil-define-command osfva-pdf-view-force-normal-state ()
:repeat abort
:suppress-operator t
(evil-normal-state)
(osfva-pdf-isearch-cleanup-highlight))
(advice-add #'pdf-isearch-mode-initialize
:before
(lambda (&rest args)
"Reset `osfva-pdf-isearch-highlight-matches'."
(setq osfva-pdf-isearch-highlight-matches nil)))
(defun osfva-pdf-isearch-mode-cleanup ()
"Don't cleanup highlight if search successfully."
(pdf-isearch-active-mode -1)
(when (osfva-isearch-failed?) (pdf-view-redisplay)))
(advice-add #'pdf-isearch-mode-cleanup
:override #'osfva-pdf-isearch-mode-cleanup)
(evil-define-key* 'normal pdf-view-mode-map
(kbd "/") #'osfva-pdf-isearch-forward
(kbd "?") #'osfva-pdf-isearch-backward
(kbd "n") #'osfva-pdf-isearch-repeat-forward
(kbd "N") #'osfva-pdf-isearch-repeat-backward
(kbd "<escape>") #'osfva-pdf-view-force-normal-state))
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还有一个问题，上面的代码仅适用于没有使用evil-collection包的情况，如果使用evil-collection，还得考虑按键绑定被evil-collection覆盖的情况，我们定义一个宏来处理，如下：
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(defmacro osfva-with-eval-after-evil-collection-mode (mode &rest body)
(declare (indent defun))
(let ((feature-name-var (gensym "feature-name"))
(mode-var (gensym "mode"))
(mode-str-var (gensym "mode-str"))
(hook-fun-name-var (gensym "hook-fun-name-var")))
`(let* ((,mode-var ,mode)
(,mode-str-var (symbol-name ,mode-var))
(,feature-name-var (intern (concat "evil-collection-" ,mode-str-var))))
(if (featurep ,feature-name-var)
;; In current implmentation of evil-collection, when the
;; file is already loaded, the setup function has also
;; called, so we can evaluate the body directly in this
;; case.
(progn ,@body)
(let ((,hook-fun-name-var
;; Intern the generated symbol, otherwise,
;; evil-collection cannot find the definition of the
;; hook function (this generally won't cause
;; conflicts because `gensym' will append a global
;; counter to the generated symbol).
(intern
(symbol-name
(gensym (concat "osfva-with-eval-after-evil-collection-mode-"
,mode-str-var))))))
(defalias ,hook-fun-name-var
(lambda (mode keymaps)
(when (eq mode ,mode-var)
,@body))
(concat "Override the things set up by the evil-collection mode " ,mode-str-var "."))
(add-hook 'evil-collection-setup-hook ,hook-fun-name-var))))))
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它做的就是判断evil-collection在对应mode的按键绑定设置完没，如果还没有，那就安排在它设置完之后再执行body设置我们的按键绑定，如果已经设置完了，那就直接执行body设置我们的按键绑定。这里使用gensym生成hook函数名，由于生成的符号是未intern的，这会导致evil-collection无法调用我们的hook函数，于是我们需要提前intern下，同时由于gensym会在符号名后面附加一个全局计数器，加上我们的函数有前缀 osfva- ，因此一般不会产生名称冲突。
hook函数则是用 defalias 定义的，因为我们的函数名是在运行时动态生成的，而 defun 不会eval函数名参数。
使用evil-collection包对应的完整代码如下：
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(with-eval-after-load 'pdf-tools
(defun osfva-isearch-failed? ()
(or (not isearch-success) isearch-error))
(defvar-local osfva-pdf-isearch-highlight-matches nil)
(defun osfva-pdf-isearch-cleanup-highlight ()
(setq osfva-pdf-isearch-highlight-matches nil)
(pdf-view-redisplay))
(defun osfva-pdf-isearch-hl-matches-controllable-highlight (orig-fun current matches &optional occur-hack-p)
(funcall orig-fun current matches (or osfva-pdf-isearch-highlight-matches occur-hack-p)))
(advice-add #'pdf-isearch-hl-matches
:around #'osfva-pdf-isearch-hl-matches-controllable-highlight)
(defvar-local osfva-pdf-isearch-forward? t)
(defun osfva-pdf-isearch-forward (&optional regexp-p no-recursive-edit)
"Like `isearch-forward', but remember the previous search direction."
(interactive "P\np")
(setq osfva-pdf-isearch-forward? t)
(isearch-forward regexp-p no-recursive-edit))
(defun osfva-pdf-isearch-backward (&optional regexp-p no-recursive-edit)
"Like `isearch-backward', but remember the previous search direction."
(interactive "P\np")
(setq osfva-pdf-isearch-forward? nil)
(isearch-backward regexp-p no-recursive-edit))
(defun osfva-pdf-isearch-repeat-forward (&optional arg)
(interactive "P")
(setq osfva-pdf-isearch-highlight-matches t)
(if osfva-pdf-isearch-forward?
(isearch-repeat-forward arg)
(isearch-repeat-backward arg)))
(defun osfva-pdf-isearch-repeat-backward (&optional arg)
(interactive "P")
(setq osfva-pdf-isearch-highlight-matches t)
(if osfva-pdf-isearch-forward?
(isearch-repeat-backward arg)
(isearch-repeat-forward arg)))
(add-hook 'pdf-view-mode-hook
(lambda () (setq-local isearch-wrap-pause 'no)))
(evil-define-command osfva-pdf-view-force-normal-state ()
:repeat abort
:suppress-operator t
(evil-normal-state)
(osfva-pdf-isearch-cleanup-highlight))
(advice-add #'pdf-isearch-mode-initialize
:before
(lambda (&rest args)
"Reset `osfva-pdf-isearch-highlight-matches'."
(setq osfva-pdf-isearch-highlight-matches nil)))
(defun osfva-pdf-isearch-mode-cleanup ()
"Don't cleanup highlight if search successfully."
(pdf-isearch-active-mode -1)
(when (osfva-isearch-failed?) (pdf-view-redisplay)))
(advice-add #'pdf-isearch-mode-cleanup
:override #'osfva-pdf-isearch-mode-cleanup)
(defmacro osfva-with-eval-after-evil-collection-mode (mode &rest body)
(declare (indent defun))
(let ((feature-name-var (gensym "feature-name"))
(mode-var (gensym "mode"))
(mode-str-var (gensym "mode-str"))
(hook-fun-name-var (gensym "hook-fun-name-var")))
`(let* ((,mode-var ,mode)
(,mode-str-var (symbol-name ,mode-var))
(,feature-name-var (intern (concat "evil-collection-" ,mode-str-var))))
(if (featurep ,feature-name-var)
;; In current implmentation of evil-collection, when the
;; file is already loaded, the setup function has also
;; called, so we can evaluate the body directly in this
;; case.
(progn ,@body)
(let ((,hook-fun-name-var
;; Intern the generated symbol, otherwise,
;; evil-collection cannot find the definition of the
;; hook function (this generally won't cause
;; conflicts because `gensym' will append a global
;; counter to the generated symbol).
(intern
(symbol-name
(gensym (concat "osfva-with-eval-after-evil-collection-mode-"
,mode-str-var))))))
(defalias ,hook-fun-name-var
(lambda (mode keymaps)
(when (eq mode ,mode-var)
,@body))
(concat "Override the things set up by the evil-collection mode " ,mode-str-var "."))
(add-hook 'evil-collection-setup-hook ,hook-fun-name-var))))))
(osfva-with-eval-after-evil-collection-mode 'pdf
(evil-define-key* 'normal pdf-view-mode-map
(kbd "/") #'osfva-pdf-isearch-forward
(kbd "?") #'osfva-pdf-isearch-backward
(kbd "n") #'osfva-pdf-isearch-repeat-forward
(kbd "N") #'osfva-pdf-isearch-repeat-backward
(kbd "<escape>") #'osfva-pdf-view-force-normal-state)))
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