Temporary clang-format configuration and script.

The format is the same as in my previous efforts here.

The script is a little tricky, since it invokes both clang-format
and codetool, and it makes sure that files do not have a changed
mtime unless there is actually some change in the file.

.clang-format

+---
+Language:        Cpp
+# Out of all supported styles, LLVM seems closest to our own.
+BasedOnStyle:    LLVM
+
+################
+#
+# Deviations from LLVM's style.
+#
+################
+
+# We prefer an indentation width of 4 columns; LLVM likes 2.
+## OVERRIDE FOR COMPARISON
+IndentWidth:     2
+
+## OVERRIDE FOR COMPARISON
+## for now i'm not sorting includes, since that makes every file get touched.
+SortIncludes: false
+
+# We prefer 79; llvm likes 80.
+ColumnLimit: 79
+
+# Where do we want to put backslashes on multiline macros?  Our choices are
+# "as far left as possible", "as far right as possible", and "make no changes."
+# LLVM defaults to right, but we don't dig that.
+AlignEscapedNewlines: Left
+
+# When we see a bunch of things in a row with comments after them, should we
+# try to align those comments?  Doing so makes some of our code pretty ugly.
+AlignTrailingComments: false
+
+# We use a function declaration style much closer to BSD KNF than to LLVM's.
+# We say:
+#      int foo(int x);
+#      int
+#      foo(int x)
+#      {
+#          ...
+#      }
+# whereas llvm prefers:
+#      int foo(int x);
+#      int foo(int x) {
+#          ...
+#      }
+# or even:
+#      int foo(int x) { ... }
+#
+BreakBeforeBraces: Custom
+BraceWrapping:
+  AfterFunction:   true
+AllowShortFunctionsOnASingleLine: None
+AlwaysBreakAfterReturnType: AllDefinitions
+
+# We don't like blocks to start with an empty line.
+#
+KeepEmptyLinesAtTheStartOfBlocks: false
+
+################
+#
+# Tor-specific magic
+#
+################
+
+#
+# These comments are magical, and should not be changed.
+#
+CommentPragmas:  'LCOV_EXCL|COVERITY'
+
+#
+# Remove duplicate empty lines.
+#
+MaxEmptyLinesToKeep: 1
+
+#
+# Indent preprocessor directives, for clarity.
+#
+IndentPPDirectives: AfterHash
+
+#
+# These introduce an iteration, and work a bit like a for loop.
+#
+# Note that we can NOT include ones that don't work like "for".  For example,
+# if the body is an argument to the macro, we can't list it here.
+#
+ForEachMacros:
+  - MAP_FOREACH
+  - MAP_FOREACH_MODIFY
+  - TOR_SIMPLEQ_FOREACH
+  - TOR_SIMPLEQ_FOREACH_SAFE
+  - TOR_SLIST_FOREACH
+  - TOR_SLIST_FOREACH_SAFE
+  - TOR_LIST_FOREACH
+  - TOR_LIST_FOREACH_SAFE
+  - TOR_TAILQ_FOREACH
+  - TOR_TAILQ_FOREACH_SAFE
+  - TOR_TAILQ_FOREACH_REVERSE
+  - TOR_TAILQ_FOREACH_REVERSE_SAFE
+  - TOR_CIRCLEQ_FOREACH
+  - TOR_CIRCLEQ_FOREACH_SAFE
+  - TOR_CIRCLEQ_FOREACH_REVERSE
+  - TOR_CIRCLEQ_FOREACH_REVERSE_SAFE
+  - HT_FOREACH
+  - SMARTLIST_FOREACH_BEGIN
+  - DIGESTMAP_FOREACH
+  - DIGESTMAP_FOREACH_MODIFY
+  - DIGEST256MAP_FOREACH
+  - DIGEST256MAP_FOREACH_MODIFY
+  - SDMAP_FOREACH
+  - RIMAP_FOREACH
+  - EIMAP_FOREACH
+
+#
+# Omitting:
+#
+# - SMARTLIST_FOREACH, since the body of the loop is an argument.
+
+#
+# This explains how to sort our headers.
+#
+# This is more complex than it truly should be, but I've edited this till
+# compilation still mostly passes.
+#
+# I'm disabling this, however, since it's a distraction from the other
+# formatting issues. See SortIncludes above.
+#
+IncludeCategories:
+  - Regex:           '^"orconfig.h'
+    Priority:        -30
+  - Regex:           '^"ext/'
+    Priority:        -18
+  - Regex:           '^"lib/'
+    Priority:        -10
+  - Regex:           '^"core/or/or.h'
+    Priority:        -5
+  - Regex:           '^"core/'
+    Priority:        5
+  - Regex:           '^"feature/'
+    Priority:        10
+  - Regex:           '^"app/'
+    Priority:        20
+
+#
+# These macros should always cause indentation, as though they were { and }.
+#
+# Do NOT put macros here unless you want an extra level of indentation between
+# them whenever they appear.
+#
+MacroBlockBegin: "^STMT_BEGIN|TT_STMT_BEGIN$"
+MacroBlockEnd:   "^STMT_END|TT_STMT_END$"
+
+#
+# These macros don't need to have semicolons afterwards.
+#
+StatementMacros:
+   - HT_PROTOTYPE
+   - HT_GENERATE
+   - HT_GENERATE2
+
+#
+# These macros are interpreted as types.
+# (Not supported in my clang-format)
+#
+# TypenameMacros:
+#    - "STACK_OF"
+
+...

scripts/maint/clang-format.sh

+#!/bin/sh
+# Copyright 2020, The Tor Project, Inc.
+# See LICENSE for licensing information.
+
+# This script runs "clang-format" and "codetool" in sequence over each of
+# our source files, and replaces the original file only if it has changed.
+#
+# We can't just use clang-format -i, since we also want to use codetool to
+# reformat a few things back to how we want them, and we want avoid changing
+# the mtime on files that didn't actually change.
+
+set -e
+
+cd "$(dirname "$0")/../../src/"
+
+# Shellcheck complains that a for loop over find's output is unreliable,
+# since there might be special characters in the output.  But we happen
+# to know that none of our C files have special characters or spaces in
+# their names, so this is safe.
+#
+# shellcheck disable=SC2044
+for fname in $(find lib core feature app test tools -name '[^.]*.[ch]'); do
+    tmpfname="${fname}.clang_fmt.tmp"
+    rm -f "${tmpfname}"
+    clang-format --style=file "${fname}" > "${tmpfname}"
+    ../scripts/maint/codetool.py "${tmpfname}"
+    if cmp "${fname}" "${tmpfname}" >/dev/null 2>&1; then
+        echo "No change in ${fname}"
+        rm -f "${tmpfname}"
+    else
+        echo "Change in ${fname}"
+        mv "${tmpfname}" "${fname}"
+    fi
+done