什么是 Infer？

Facebook 的 Infer 是一个静态分析工具。Infer 可以分析 Objective-C， Java 或者 C 代码，报告潜在的问题。

任何人都可以使用 Infer 检测应用，这可以将那些严重的 bug 扼杀在发布之前，同时防止应用崩溃和性能低下。
这是infer的官网，更加详细的资料可以在上面查看。

因为刚开始接触infer，只是了解了最基本的一些使用，后续有一些新的了解都会在该篇文章上做记录。

安装infer

最简单的安装方法就是使用Homebrew，可能需要翻墙。

brew install infer

当你运行再linux或者不想使用homebrew安装的时候，你可以使用最新的release版本。

VERSION=0.XX.Y; \
curl -sSL "https://github.com/facebook/infer/releases/download/v$VERSION/infer-linux64-v$VERSION.tar.xz" \
| sudo tar -C /opt -xJ && \
ln -s "/opt/infer-linux64-v$VERSION/bin/infer" /usr/local/bin/infer

使用infer

官网中是以hello world为例来讲解。这边就偷懒直接引用官方的例子

Hello world Objective-C

以下是一个简单的 Objective-C 例子：

// Hello.m
#import <Foundation/Foundation.h>

@interface Hello: NSObject
@property NSString* s;
@end

@implementation Hello
NSString* m() {
    Hello* hello = nil;
    return hello->_s;
}
@end

在 Hello.m 同级目录，运行：

infer run -- clang -c Hello.m

以下是错误报告输出：

Hello.m:10 NULL_DEREFERENCE
  pointer hello last assigned on line 9 could be null and is dereferenced at line 10, column 12

编辑，如下修正：

NSString* m() {
    Hello* hello = nil;
    return hello.s;
}

再次运行，No issues found，没有报错。

Hello world iOS

iOS 的示例代码在这里 infer/examples/ios_hello，使用 Infer 检测：

infer run -- xcodebuild -target HelloWorldApp -configuration Debug -sdk iphonesimulator

将会有以下问题输出：

AppDelegate.m:20: error: MEMORY_LEAK
   memory dynamically allocated to shadowPath by call to CGPathCreateWithRect() at line 20, column 28 is not reachable after line 20, column 5

AppDelegate.m:25: error: RESOURCE_LEAK
   resource acquired to fp by call to fopen() at line 25, column 8 is not released after line 25, column 5

AppDelegate.m:29: warning: PARAMETER_NOT_NULL_CHECKED
   Parameter callback is not checked for null, there could be a null pointer dereference: pointer callback could be null and is dereferenced at line 29, column 5

AppDelegate.m:34: error: NULL_DEREFERENCE
   pointer str last assigned on line 33 could be null and is dereferenced at line 34, column 12

AppDelegate.m:39: error: PREMATURE_NIL_TERMINATION_ARGUMENT
   pointer str last assigned on line 38 could be nil which results in a call to arrayWithObjects: with 1 arguments instead of 3 (nil indicates that the last argument of this variadic method has been reached) at line 39, column 12

Hello.m:20: error: NULL_DEREFERENCE
   pointer hello last assigned on line 19 could be null and is dereferenced at line 20, column 12

Hello.m:25: warning: IVAR_NOT_NULL_CHECKED
   Instance variable hello -> _hello is not checked for null, there could be a null pointer dereference: pointer ret_hello last assigned on line 24 could be null and is dereferenced at line 25, column 12

Hello.m:30: warning: PARAMETER_NOT_NULL_CHECKED
   Parameter hello is not checked for null, there could be a null pointer dereference: pointer ret_hello last assigned on line 29 could be null and is dereferenced at line 30, column 12

和gradle, 运行同样的命令第二次，可能得不到分析结果，由于没有重新编译，需要使用 ----reactive (或 -r) 使得增量编译有结果输出。

infer run --reactive -- xcodebuild -target HelloWorldApp -configuration Debug -sdk iphonesimulator

或者在编译前清理：

xcodebuild -target HelloWorldApp -configuration Debug -sdk iphonesimulator clean

现在大多项目都是以workspace的形式，那么workspace怎么使用infer来检测呢？

infer run -- xcodebuild -workspace <your name>.xcworkspace -scheme <your scheme> -configuration Debug -sdk iphonesimulator

运行成功之后，会在根目录下生成infer-out文件目录，里面包含分析日志。

infer-log

其中bugs.txt中就是infer分析之后检测出的问题所在，我们就可以通过该信息修复潜在的问题。
下面是infer跑本地demo输出的信息。

Found 4 issues

directory/ViewController.m:21: error: RETAIN_CYCLE
  Retain cycle at line 21, column 10 involving the following objects:
 (1) a block that captures `self`
 (2) object of type `ViewController*` --> `_testBlock`, last assigned on line 21.
  19.   
  20.   - (void)test {
  21. >     self.testBlock = ^{
  22.           NSLog(@"%@", self.age);
  23.       };
...
Summary of the reports

  BAD_POINTER_COMPARISON: 2
            RETAIN_CYCLE: 1
  ASSIGN_POINTER_WARNING: 1