JS: support React getSnapshotBeforeUpdate

Author: Esben Sparre Andreasen

javascript/ql/src/semmle/javascript/frameworks/React.qll

@@ -207,6 +207,10 @@ abstract class ReactComponent extends ASTNode {
       // getDerivedStateFromProps: (props, state)
       callback = getStaticMethod("getDerivedStateFromProps").flow() and
       stateParameterIndex = 1
+      or
+      // getSnapshotBeforeUpdate: (prevProps, prevState)
+      callback = getInstanceMethod("getSnapshotBeforeUpdate").flow() and
+      stateParameterIndex = 1
     )
   }
 
@@ -258,6 +262,11 @@ abstract class ReactComponent extends ASTNode {
       // getDerivedStateFromProps: (props, state)
       callback = getStaticMethod("getDerivedStateFromProps").flow() and
       propsParameterIndex = 0
+      or
+      // getSnapshotBeforeUpdate: (prevProps, prevState)
+      callback = getInstanceMethod("getSnapshotBeforeUpdate").flow() and
+      propsParameterIndex = 0
+
     )
   }
 

javascript/ql/test/library-tests/frameworks/ReactJS/ReactComponent_getAPreviousStateSource.expected

@@ -1,3 +1,4 @@
 | rare-lifecycle-methods.js:1:1:11:1 | class C ...     }\\n} | rare-lifecycle-methods.js:2:44:2:48 | state |
+| rare-lifecycle-methods.js:1:1:11:1 | class C ...     }\\n} | rare-lifecycle-methods.js:8:40:8:48 | prevState |
 | statePropertyReads.js:1:1:13:1 | class R ...     }\\n} | statePropertyReads.js:7:24:7:32 | prevState |
 | statePropertyReads.js:1:1:13:1 | class R ...     }\\n} | statePropertyReads.js:10:35:10:43 | prevState |