clang-format malfunctioning(?) Or am I not fully understanding how clang-format works?

Question

I installed the clang-format package from melpa.
I then added the following lines to my init file:

(require 'clang-format)

I then created a test directory, cpp-proj with one file, main.cpp.

main.cpp

#include <iostream>

using namespace std;

int main()
{
    cout << "ok\n";
    return 0;
}

I then created a .clang-format file in the directory using the command:

clang-format -style=webkit -dump-config > .clang-format

.clang-format

---
Language:        Cpp
# BasedOnStyle:  WebKit
AccessModifierOffset: -4
AlignAfterOpenBracket: DontAlign
AlignConsecutiveAssignments: false
AlignConsecutiveDeclarations: false
AlignEscapedNewlinesLeft: false
AlignOperands:   false
AlignTrailingComments: false
AllowAllParametersOfDeclarationOnNextLine: true
AllowShortBlocksOnASingleLine: false
AllowShortCaseLabelsOnASingleLine: false
AllowShortFunctionsOnASingleLine: All
AllowShortIfStatementsOnASingleLine: false
AllowShortLoopsOnASingleLine: false
AlwaysBreakAfterDefinitionReturnType: None
AlwaysBreakAfterReturnType: None
AlwaysBreakBeforeMultilineStrings: false
AlwaysBreakTemplateDeclarations: false
BinPackArguments: true
BinPackParameters: true
BraceWrapping:   
  AfterClass:      false
  AfterControlStatement: false
  AfterEnum:       false
  AfterFunction:   true
  AfterNamespace:  false
  AfterObjCDeclaration: false
  AfterStruct:     false
  AfterUnion:      false
  BeforeCatch:     false
  BeforeElse:      false
  IndentBraces:    false
BreakBeforeBinaryOperators: All
BreakBeforeBraces: WebKit
BreakBeforeTernaryOperators: true
BreakConstructorInitializersBeforeComma: true
ColumnLimit:     0
CommentPragmas:  '^ IWYU pragma:'
ConstructorInitializerAllOnOneLineOrOnePerLine: false
ConstructorInitializerIndentWidth: 4
ContinuationIndentWidth: 4
Cpp11BracedListStyle: false
DerivePointerAlignment: false
DisableFormat:   false
ExperimentalAutoDetectBinPacking: false
ForEachMacros:   [ foreach, Q_FOREACH, BOOST_FOREACH ]
IncludeCategories: 
  - Regex:           '^"(llvm|llvm-c|clang|clang-c)/'
    Priority:        2
  - Regex:           '^(<|"(gtest|isl|json)/)'
    Priority:        3
  - Regex:           '.*'
    Priority:        1
IndentCaseLabels: false
IndentWidth:     4
IndentWrappedFunctionNames: false
KeepEmptyLinesAtTheStartOfBlocks: true
MacroBlockBegin: ''
MacroBlockEnd:   ''
MaxEmptyLinesToKeep: 1
NamespaceIndentation: Inner
ObjCBlockIndentWidth: 4
ObjCSpaceAfterProperty: true
ObjCSpaceBeforeProtocolList: true
PenaltyBreakBeforeFirstCallParameter: 19
PenaltyBreakComment: 300
PenaltyBreakFirstLessLess: 120
PenaltyBreakString: 1000
PenaltyExcessCharacter: 1000000
PenaltyReturnTypeOnItsOwnLine: 60
PointerAlignment: Left
ReflowComments:  true
SortIncludes:    true
SpaceAfterCStyleCast: false
SpaceBeforeAssignmentOperators: true
SpaceBeforeParens: ControlStatements
SpaceInEmptyParentheses: false
SpacesBeforeTrailingComments: 1
SpacesInAngles:  false
SpacesInContainerLiterals: true
SpacesInCStyleCastParentheses: false
SpacesInParentheses: false
SpacesInSquareBrackets: false
Standard:        Cpp03
TabWidth:        8
UseTab:          Never
...

I then went back into my main.cpp file, with the whole buffer selected and issued the command Meta-x clang-format-region.
The result:

main.cpp

#include <iostream>

using namespace std;

int main() {
  cout << "ok\n" << endl;
  return 0;
}

This is not correct.

It should be:

main.cpp

#include <iostream>

using namespace std;

int main()
{
    cout << "ok\n"
         << endl;
    return 0;
}

No matter what style I choose it doesn't work within emacs.

Am I doing something wrong configuring clang-format?
It spits out the correct format when I issue the command
clang-format -style="<style>" main.cpp in a terminal, but never in Emacs!
What gives?

Answer 1

I found the same thing (not following my styles as defined in a .clang-format file, which happens to be in the parent directory in my case), and I think that the problem is in the way that the assume-file-name argument is defaulted if absent when calling the function clang-format-region from clang-format.el:

(unless assume-file-name (setq assume-file-name buffer-file-name))

Further down, this is passed to the -assume-filename command-line option of clang-format. This means that we ask clang-format to look in files with the same name as the current buffer for the style information, which didn't seem like a good default to me. I therefore experimentally altered the default to be .clang-format, thus:

(unless assume-file-name (setq assume-file-name '".clang-format"))

That way we look in the "usual place" for the style info. In my case this solved the problem and my style file is honoured when running clang-format via the emacs function.

It might be preferable to alter the arguments which are passed to the clang-format-region function instead of altering the default like this, but to me .clang-format felt like a more sensible default than the name of the current buffer!