Don't lint against Hooks after conditional throw

Seems like this should be OK. Fixes #14038.

Now when tracking paths, we completely ignore segments that end in a throw. In https://eslint.org/docs/developer-guide/code-path-analysis I don't see a way to detect throws other than manually tracking them, so that's what I've done.

Author: sophiebits

packages/eslint-plugin-react-hooks/__tests__/ESLintRulesOfHooks-test.js

@@ -261,6 +261,15 @@ eslintTester.run('react-hooks', ReactHooksESLintRule, {
         useState();
       }
     `,
+    `
+      // Valid because exceptions abort rendering
+      function RegressionTest() {
+        if (page == null) {
+          throw new Error('oh no!');
+        }
+        useState();
+      }
+    `,
   ],
   invalid: [
     {

packages/eslint-plugin-react-hooks/src/RulesOfHooks.js

@@ -71,20 +71,25 @@ export default {
   create(context) {
     const codePathReactHooksMapStack = [];
     const codePathSegmentStack = [];
+    const codePathThrowingSegmentsStack = [];
     return {
       // Maintain code segment path stack as we traverse.
       onCodePathSegmentStart: segment => codePathSegmentStack.push(segment),
       onCodePathSegmentEnd: () => codePathSegmentStack.pop(),
 
       // Maintain code path stack as we traverse.
-      onCodePathStart: () => codePathReactHooksMapStack.push(new Map()),
+      onCodePathStart: () => {
+        codePathReactHooksMapStack.push(new Map());
+        codePathThrowingSegmentsStack.push(new Set());
+      },
 
       // Process our code path.
       //
       // Everything is ok if all React Hooks are both reachable from the initial
       // segment and reachable from every final segment.
       onCodePathEnd(codePath, codePathNode) {
         const reactHooksMap = codePathReactHooksMapStack.pop();
+        const throwingSegments = codePathThrowingSegmentsStack.pop();
         if (reactHooksMap.size === 0) {
           return;
         }
@@ -115,6 +120,10 @@ export default {
          */
 
         function countPathsFromStart(segment) {
+          if (throwingSegments.has(segment)) {
+            return 0;
+          }
+
           const {cache} = countPathsFromStart;
           let paths = cache.get(segment.id);
 
@@ -175,6 +184,10 @@ export default {
          */
 
         function countPathsToEnd(segment) {
+          if (throwingSegments.has(segment)) {
+            return 0;
+          }
+
           const {cache} = countPathsToEnd;
           let paths = cache.get(segment.id);
 
@@ -462,6 +475,12 @@ export default {
           reactHooks.push(node.callee);
         }
       },
+
+      ThrowStatement(node) {
+        const throwingSegments = last(codePathThrowingSegmentsStack);
+        const codePathSegment = last(codePathSegmentStack);
+        throwingSegments.add(codePathSegment);
+      },
     };
   },
 };