[PATCH v3] Add .clang-format style file

[Florian Weimer]

* Noah Goldstein via Libc-alpha:

> Went with version >= 11.0 since it covers most of the major features
> and should be pretty universally accessibly.
>
> There are some issues:
>
> 1.  indention of preprocessor directives:
>     Unfortunately there doesn't appear to be a switch for a seperate
>     'IndentWidth' for preprocessor directives vs. normal code so we
>     are stuck either not indenting the directives or over-indenting
>     them. i.e:
>     Desired:
>     ```
>     #ifndef A
>     # define B
>     #endif
>     ```
>     Options:
>     ```
>     #ifndef A
>     #  define B /* Two spaces instead of one.  */
>     #endif
>
>     #ifndef C
>     #define D   /* No spaces.  */
>     #endif
>     ```
>     Chose to over-indent as it generally seems easier to script
>     halving all pre-processor indentations than counting the nested
>     depth and indenting from scratch.
>
> 2.  concatenation of lines missing semi-colons:
>     Throughout glibc there are macros used to setup aliasing that are
>     outside of functions and don't end in semi-colons i.e:
>     ```
>     libc_hidden_def (__pthread_self)
>     weak_alias (__pthread_self, pthread_self)
>     ```
>
>     clang-format reformats lines like these to:
>     ```
>     libc_hidden_def (__pthread_self) weak_alias (__pthread_self, pthread_self)
>     ```
>
>     which is generally undesirable.
>
> Other than those two big concerns there are certainly some questions
> diffs but for the most part it creates a easy to read and consistent
> style.
> ---
>  .clang-format | 175 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 175 insertions(+)
>  create mode 100644 .clang-format
>
> diff --git a/.clang-format b/.clang-format
> new file mode 100644
> index 0000000000..fcb344ef70
> --- /dev/null
> +++ b/.clang-format
> @@ -0,0 +1,175 @@
> +#  clang-format file for GLIBC
> +#  Copyright (C) 2022 Free Software Foundation, Inc.
> +#  This file is part of the GNU C Library.
> +#
> +#  The GNU C Library is free software; you can redistribute it and/or
> +#  modify it under the terms of the GNU Lesser General Public
> +#  License as published by the Free Software Foundation; either
> +#  version 2.1 of the License, or (at your option) any later version.
> +#
> +#  The GNU C Library is distributed in the hope that it will be useful,
> +#  but WITHOUT ANY WARRANTY; without even the implied warranty of
> +#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +#  Lesser General Public License for more details.
> +#
> +#  You should have received a copy of the GNU Lesser General Public
> +#  License along with the GNU C Library; if not, see
> +#  <https://www.gnu.org/licenses/>.
> +#
> +#  Requires clang-format version >= 11.0
> +#
> +#  For more information, see:
> +#
> +#   Documentation/process/clang-format.rst

That's not a valid path in the glibc source tree.

> +# BasedOnStyle:  GNU

Why is this commented out?

> +AccessModifierOffset: -2
> +AlignAfterOpenBracket: Align
> +AlignConsecutiveMacros: false
> +AlignConsecutiveAssignments: false
> +AlignConsecutiveBitFields: false
> +AlignConsecutiveDeclarations: false
> +AlignEscapedNewlines: Right
> +AlignOperands:   true
> +AlignTrailingComments: true
> +AllowAllArgumentsOnNextLine: true
> +AllowAllConstructorInitializersOnNextLine: true
> +AllowAllParametersOfDeclarationOnNextLine: true
> +AllowShortEnumsOnASingleLine: true
> +AllowShortBlocksOnASingleLine: false
> +AllowShortCaseLabelsOnASingleLine: false
> +AllowShortFunctionsOnASingleLine: All
> +AllowShortLambdasOnASingleLine: All
> +AllowShortIfStatementsOnASingleLine: Never
> +AllowShortLoopsOnASingleLine: false
> +AlwaysBreakAfterDefinitionReturnType: All
> +AlwaysBreakAfterReturnType: AllDefinitions
> +AlwaysBreakBeforeMultilineStrings: false
> +AlwaysBreakTemplateDeclarations: MultiLine
> +BinPackArguments: true
> +BinPackParameters: true
> +BraceWrapping:
> +  AfterCaseLabel:  true
> +  AfterClass:      true
> +  AfterControlStatement: true
> +  AfterEnum:       true
> +  AfterFunction:   true
> +  AfterNamespace:  true
> +  AfterStruct:     true
> +  AfterUnion:      true
> +  AfterExternBlock: true
> +  BeforeCatch:     true
> +  BeforeElse:      true
> +  BeforeWhile:     true
> +  IndentBraces:    true
> +  SplitEmptyFunction: true
> +  SplitEmptyRecord: true
> +  SplitEmptyNamespace: true
> +BreakBeforeBinaryOperators: All
> +BreakBeforeBraces: GNU
> +BreakBeforeInheritanceComma: false
> +BreakInheritanceList: BeforeColon
> +BreakBeforeTernaryOperators: true
> +BreakConstructorInitializersBeforeComma: false
> +BreakConstructorInitializers: BeforeColon
> +BreakStringLiterals: true
> +ColumnLimit:     79
> +CommentPragmas:  '^ IWYU pragma:'
> +CompactNamespaces: false
> +ConstructorInitializerAllOnOneLineOrOnePerLine: false
> +ConstructorInitializerIndentWidth: 4
> +ContinuationIndentWidth: 4
> +Cpp11BracedListStyle: false
> +DeriveLineEnding: true
> +DerivePointerAlignment: false
> +DisableFormat:   false
> +ExperimentalAutoDetectBinPacking: false
> +FixNamespaceComments: false
> +ForEachMacros:
> +  - foreach
> +  - Q_FOREACH
> +  - BOOST_FOREACH

> +IncludeBlocks:   Preserve
> +IncludeCategories:
> +  - Regex:           '^"(llvm|llvm-c|clang|clang-c)/'
> +    Priority:        2
> +  - Regex:           '^(<|"(gtest|gmock|isl|json)/)'
> +    Priority:        3
> +  - Regex:           '.*'
> +    Priority:        1

These regular expression do not seem to be relevant to glibc.

> +UseTab:          Never

I prefer not using tabs, but others disagree, and most of the source
files use tabs instead of 8 spaces (and not just for indentation).

> +ForEachMacros:
> +  - 'FOR_EACH_IMPL'
> +  - 'list_for_each'
> +  - 'list_for_each_prev'
> +  - 'list_for_each_prev_safe'

If this is a YAML file, do these duplicate FoEachMacros keys have any
effect?  Only the second one is relevant to glibc.