Introduce g:clang_format#praise and avoid changes

Avoid add unnecessary items to the change-list if the code is already
formatted according to clang-format.

Add a cheerful echo to praise the user (positive nudging?). However,
some users might not be pleased by that, so introduce a way to disable
the joyful echo.

Author: Kypert

README.md

@@ -116,6 +116,12 @@ When the value is 0, `-fallback-style=none` option is added on executing clang-f
 It means that vim-clang-format does nothing when `.clang-format` is not found.
 The default value is 1.
 
+- `g:clang_format#praise`
+
+When the value is 1, you will be praised for already having well-formatted code.
+Some users might not want/need praise, thus providing this variable.
+The default value is 1.
+
 ## Vimrc Example
 
 ```vim

autoload/clang_format.vim

@@ -191,6 +191,7 @@ let g:clang_format#filetype_style_options = s:getg('clang_format#filetype_style_
 
 let g:clang_format#detect_style_file = s:getg('clang_format#detect_style_file', 1)
 let g:clang_format#enable_fallback_style = s:getg('clang_format#enable_fallback_style', 1)
+let g:clang_format#praise = s:getg('clang_format#praise', 1)
 
 let g:clang_format#auto_format = s:getg('clang_format#auto_format', 0)
 let g:clang_format#auto_format_on_insert_leave = s:getg('clang_format#auto_format_on_insert_leave', 0)
@@ -238,6 +239,13 @@ function! clang_format#replace(line1, line2, ...) abort
 
     let winview = winsaveview()
     let splitted = split(formatted, '\n', 1)
+    if getline(a:line1, a:line2) ==# splitted[a:line1-1:a:line2-1]
+        if g:clang_format#praise
+            echo "No formatting needed, looking fabulous already!"
+        endif
+        " Early out, no need to introduce a change
+        return
+    endif
 
     silent! undojoin
     if line('$') > len(splitted)

doc/clang-format.txt

@@ -206,6 +206,13 @@ g:clang_format#enable_fallback_style	  *g:clang_format#enable_fallback_style*
     ".clang-format" is not found.
     The default value is 1.
 
+g:clang_format#praise                                    *g:clang_format#praise*
+
+    When the value is 1, |vim-clang-format| will praise you for already having
+    well-formatted code.  Some users might not want/need praise, thus
+    providing this variable.
+    The default value is 1.
+
 
 
 ==============================================================================

test/t/clang_format_spec.vim

@@ -99,6 +99,7 @@ describe 'default settings'
         Expect exists('g:clang_format#filetype_style_options') to_be_true
         Expect exists('g:clang_format#command') to_be_true
         Expect exists('g:clang_format#detect_style_file') to_be_true
+        Expect exists('g:clang_format#praise') to_be_true
         Expect exists('g:clang_format#auto_format') to_be_true
         Expect exists('g:clang_format#auto_format_on_insert_leave') to_be_true
         Expect g:clang_format#extra_args to_be_empty
@@ -107,6 +108,7 @@ describe 'default settings'
         Expect g:clang_format#filetype_style_options to_be_empty
         Expect executable(g:clang_format#command) to_be_true
         Expect g:clang_format#detect_style_file to_be_true
+        Expect g:clang_format#praise to_be_true
     end
 
     it 'provide commands'