最近写SDK的时候需要用到object类型提示符，PHPStorm智能提示说需要PHP7.2以上才能支持这种类型提示。
我一查我本机的PHP是7.1.30版本，于是考虑升级一下PHP版本。
首先要尝试使用如下命令进行升级：

brew update 
brew upgrade php@7.4

第一个遇到的报错如下所示：

git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core fetch --unshallow
This restriction has been made on GitHub's request because updating shallow
clones is an extremely expensive operation due to the tree layout and traffic of
Homebrew/homebrew-core and Homebrew/homebrew-cask. We don't do this for you
automatically to avoid repeatedly performing an expensive unshallow operation in
CI systems (which should instead be fixed to not use shallow clones). Sorry for
the inconvenience!

然后按照提醒执行"git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core fetch --unshallow"命令还会报错：

fatal: dumb http transport does not support shallow capabilities

由此怀疑homebrew-core的源可能因为一些不可抗力的原因无法正常使用，从而导致fetch操作失败。可以考虑换成国内的源，编写shell如下所示：

# 切换到homebrew-core目录下
cd "$(brew --repo)/Library/Taps/homebrew/homebrew-core"
# 设置homebrew源为国内的中科大镜像
git remote set-url origin https://mirrors.ustc.edu.cn/homebrew-core.git
# 更新homebrew-core
git -C /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core fetch --unshallow

执行之后可以看到如下输出，然后就可以顺利执行brew update了。

remote: Enumerating objects: 539863, done.
remote: Counting objects: 100% (539826/539826), done.
remote: Compressing objects: 100% (194417/194417), done.
remote: Total 530481 (delta 341532), reused 521981 (delta 333211)
Receiving objects: 100% (530481/530481), 191.29 MiB | 9.18 MiB/s, done.
Resolving deltas: 100% (341532/341532), completed with 8120 local objects.

安装php7.4的方法很简单，可以使用源码下载编译的方法：

brew install --build-from-source php@7.4

可以看到大量输出，最后没有报错就可以完成php7.4的安装啦。

要让终端里面之前的PHP版本切换成功还需要在.bash_profile中设置环境变量，添加如下语句：

export PATH="/usr/local/opt/php@7.4/bin:$PATH"
export PATH="/usr/local/opt/php@7.4/sbin:$PATH"

最后执行source ~/.bash_profile命令完成生效操作。

为了确认是否真的生效，可以执行如下命令php -v
得到输出如下即为正确:

PHP 7.4.15 (cli) (built: Feb 21 2021 20:08:10) ( NTS )
Copyright (c) The PHP Group
Zend Engine v3.4.0, Copyright (c) Zend Technologies
    with Zend OPcache v7.4.15, Copyright (c), by Zend Technologies

参考的资料如下：

1. homebrew国内源替换办法
2. php7.2升级到php7.4