EDIT 2021: NOT WORKING ANYMORE!! clang-format version 7 (7.0.0) formula for brew (check comment below on how to install it)

clang-format@7.rb

class ClangFormatAT7 < Formula
  desc "Formatting tool for C/C++/Java/JavaScript/Objective-C/Protobuf"
  homepage "https://releases.llvm.org/7.0.0/tools/clang/docs/ClangFormat.html"
  version "7.0.0"

  if MacOS.version >= :sierra
    url "https://llvm.org/svn/llvm-project/llvm/tags/RELEASE_700/final/", :using => :svn
  else
    url "http://llvm.org/svn/llvm-project/llvm/tags/RELEASE_700/final/", :using => :svn
  end

  depends_on "cmake" => :build
  depends_on "ninja" => :build
  depends_on "subversion" => :build

  resource "clang" do
    if MacOS.version >= :sierra
      url "https://llvm.org/svn/llvm-project/cfe/tags/RELEASE_700/final/", :using => :svn
    else
      url "http://llvm.org/svn/llvm-project/cfe/tags/RELEASE_700/final/", :using => :svn
    end
  end

  resource "libcxx" do
    url "https://releases.llvm.org/7.0.0/libcxx-7.0.0.src.tar.xz"
    sha256 "9b342625ba2f4e65b52764ab2061e116c0337db2179c6bce7f9a0d70c52134f0"
  end

  def install
    (buildpath/"projects/libcxx").install resource("libcxx")
    (buildpath/"tools/clang").install resource("clang")

    mkdir "build" do
      args = std_cmake_args
      args << "-DCMAKE_OSX_SYSROOT=/" unless MacOS::Xcode.installed?
      args << "-DLLVM_ENABLE_LIBCXX=ON"
      args << ".."
      system "cmake", "-G", "Ninja", *args
      system "ninja", "clang-format"
      bin.install "bin/clang-format"
    end
    bin.install "tools/clang/tools/clang-format/git-clang-format"
    (share/"clang").install Dir["tools/clang/tools/clang-format/clang-format*"]
  end

  test do
    # NB: below C code is messily formatted on purpose.
    (testpath/"test.c").write <<~EOS
      int         main(char *args) { \n   \t printf("hello"); }
    EOS

    assert_equal "int main(char *args) { printf(\"hello\"); }\n",
        shell_output("#{bin}/clang-format -style=Google test.c")

    # below code is messily formatted on purpose.
    (testpath/"test2.h").write <<~EOS
      #import  "package/file.h"
      @interface SomePlugin   : NSObject  < ParentPlugin >
      @end
    EOS

    # NOTE! different formatting depending on version
    # clang-format 5.x
    #     @interface SomePlugin : NSObject<ParentPlugin>
    # clang-format 6.x, 7.x
    #     @interface SomePlugin : NSObject <ParentPlugin>
    assert_equal "#import \"package/file.h\"\n@interface SomePlugin : NSObject <ParentPlugin>\n@end\n",
        shell_output("#{bin}/clang-format -style=Google test2.h")
  end
end

Hi @ffeu. Thanks for this. I'm stuck in the installation.
Could you please have a look and see if you can help me point the error at the top of your head.

The issue is I'm not able to move ahead of this step. It's over 4 hours since it has been cloning the repository.
I tried running brew install clang-format and it works fine. But the requirement dictates me to have version 7.0. Could you see what might be going wrong?
Thanks!

try taking a look where it clones the repository and try to do it manually (clone it manually), it's looks like the problem is related to that...

As llvm.org/svn seems not working (forbidden), one can use pre-built binary from https://releases.llvm.org/download.html

For example, for 7.0.0 and macOS:

• Download https://releases.llvm.org/7.0.0/clang+llvm-7.0.0-x86_64-apple-darwin.tar.xz
• Extract archive
• Add <path to extracted folder>/bin to path
• Use clang-format command!