RestrictedApi

```
@Target({CONSTRUCTOR,METHOD})
public @interface RestrictedApi
```
Restrict this method to callsites with a allowlist annotation.
Callers that are not allowlisted will cause a configurable compiler diagnostic. Allowlisting can either allow the call outright, or make the compiler emit a warning when the API is called. Paths matching a regular expression, e.g. unit tests, can also be excluded.
The following example shows a hypothetical, potentially unsafe Foo.bar method. It is marked with the @RestrictedApi annotations such that callers annotated with @LegacyUnsafeFooBar raise a warning, whereas the @ReviewedFooBar annotation silently allows the call.
The @LegacyUnsafeFooBar annotation can be used to allow existing call sites until they are refactored, while prohibiting new call-sites. Call-sites determined to be acceptable, for example through code review, could be marked @ReviewedFooBar.
```
{@code
 public @interface LegacyUnsafeFooBar{}

 public @interface ReviewedFooBar{
  public string reviewer();
  public string comments();
 }

 public class Foo {
```

Required Element Summary

Required Elements
Modifier and Type Required Element Description

java.lang.String explanation
Explanation why the API is restricted, to be inserted into the compiler output.

Optional Element Summary

Optional Elements
Modifier and Type	Optional Element	Description
`java.lang.String`	`allowedOnPath`	Allow the restricted API on paths matching this regular expression.
`java.lang.Class<? extends java.lang.annotation.Annotation>[]`	`allowlistAnnotations`	Allow calls to the restricted API in methods or classes with this annotation.
`java.lang.Class<? extends java.lang.annotation.Annotation>[]`	`allowlistWithWarningAnnotations`	Emit warnings, not errors, on calls to the restricted API for callers with this annotation.
`java.lang.String`	`link`	Optional link explaining why the API is restricted.

- Element Detail
  - explanation
```
java.lang.String explanation
```
    Explanation why the API is restricted, to be inserted into the compiler output.
- - link
```
java.lang.String link
```
    Optional link explaining why the API is restricted.
    
    Default:
    
    ""
- - allowedOnPath
```
java.lang.String allowedOnPath
```
    Allow the restricted API on paths matching this regular expression.
    Leave empty (the default) to enforce the API restrictions on all paths.
    
    Default:
    
    ""
- - allowlistAnnotations
```
java.lang.Class<? extends java.lang.annotation.Annotation>[] allowlistAnnotations
```
    Allow calls to the restricted API in methods or classes with this annotation.
    
    Default:
    
    {}
- - allowlistWithWarningAnnotations
```
java.lang.Class<? extends java.lang.annotation.Annotation>[] allowlistWithWarningAnnotations
```
    Emit warnings, not errors, on calls to the restricted API for callers with this annotation.
    This should only be used if callers should aggressively move away from this API (or change to a allowlist annotation after review). Too many warnings will lead to ALL warnings being ignored, so tread very carefully.
    
    Default:
    
    {}