[PATCH v3] Add .clang-format style file

[Fangrui Song]

On 2022-03-30, Noah Goldstein via Libc-alpha wrote:
>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.

Thanks. I have spot checked a few files and having the file will be
helpful.

Side note: clang-format works even without .clang-format and falls back to LLVM
style. Having the file makes the format rules actually reflect the glibc coding
standard.

Reviewed-by: Fangrui Song <maskray@google.com>

>---
> .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
>+#   https://clang.llvm.org/docs/ClangFormat.html
>+#   https://clang.llvm.org/docs/ClangFormatStyleOptions.html
>+#
>+#  There are some known cases that this doesn't produce the desired
>+#  style (i.e Preprocessor Directives are over-indented and not
>+#  auto-commented). As a result, this is meant to be a utility to make
>+#  formatting easier, not a definitive standard.
>+#
>+#  To format the current git diff inplace (-i) the follow command can
>+#  be used:
>+#  $> git diff -U0 --no-color HEAD^ | clang-format-diff -i -p1
>+#
>+#  To just view the diff clang-format would generate:
>+#  $> git diff -U0 --no-color HEAD^ | clang-format-diff -p1
>+#
>+#  NB: clang-format-diff, along with other clang-format related tools,
>+#      can be found at: /path/to/llvm-project/clang/tools/clang-format/
>+#

The ability to re-format blocks of code is especially useful for
contributors sending patches. Thanks for highlighting it.

>+#
>+---
>+# BasedOnStyle:  GNU
>+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
>+IncludeIsMainRegex: '(Test)?$'
>+IndentCaseLabels: false
>+IndentCaseBlocks: false
>+IndentGotoLabels: true
>+IndentWidth:     2
>+IndentPPDirectives: AfterHash
>+IndentExternBlock: AfterExternBlock
>+IndentWrappedFunctionNames: false
>+InsertTrailingCommas: None
>+KeepEmptyLinesAtTheStartOfBlocks: true
>+MacroBlockBegin: ''
>+MacroBlockEnd:   ''
>+MaxEmptyLinesToKeep: 1
>+NamespaceIndentation: None
>+PenaltyBreakAssignment: 2
>+PenaltyBreakBeforeFirstCallParameter: 19
>+PenaltyBreakComment: 300
>+PenaltyBreakFirstLessLess: 120
>+PenaltyBreakString: 1000
>+PenaltyBreakTemplateDeclaration: 10
>+PenaltyExcessCharacter: 1000000
>+PenaltyReturnTypeOnItsOwnLine: 60
>+PointerAlignment: Right
>+ReflowComments:  true
>+SortIncludes:    false
>+SortUsingDeclarations: true
>+SpaceAfterCStyleCast: true
>+SpaceAfterLogicalNot: false
>+SpaceAfterTemplateKeyword: true
>+SpaceBeforeAssignmentOperators: true
>+SpaceBeforeCpp11BracedList: false
>+SpaceBeforeCtorInitializerColon: true
>+SpaceBeforeInheritanceColon: true
>+SpaceBeforeParens: Always
>+SpaceBeforeRangeBasedForLoopColon: true
>+SpaceInEmptyBlock: false
>+SpaceInEmptyParentheses: false
>+SpacesBeforeTrailingComments: 1
>+SpacesInAngles:  false
>+SpacesInConditionalStatement: false
>+SpacesInContainerLiterals: true
>+SpacesInCStyleCastParentheses: false
>+SpacesInParentheses: false
>+SpacesInSquareBrackets: false
>+SpaceBeforeSquareBrackets: false
>+Standard:        Cpp03
>+StatementMacros:
>+  - Q_UNUSED
>+  - QT_REQUIRE_VERSION
>+TabWidth:        8
>+UseTab:          Never
>+ForEachMacros:
>+  - 'FOR_EACH_IMPL'
>+  - 'list_for_each'
>+  - 'list_for_each_prev'
>+  - 'list_for_each_prev_safe'
>+...
>-- 
>2.25.1
>