Validator pass that terminal successors all exist

compiler/forget/src/CompilerPipeline.ts

@@ -11,9 +11,10 @@ import {
   lower,
   mergeConsecutiveBlocks,
   ReactiveFunction,
+  validateConsistentIdentifiers,
+  validateTerminalSuccessors,
 } from "./HIR";
 import { Environment, EnvironmentConfig } from "./HIR/Environment";
-import { validateConsistentIdentifiers } from "./HIR/ValidateConsistentIdentifiers";
 import {
   analyseFunctions,
   dropMemoCalls,
@@ -61,6 +62,7 @@ export function* run(
   yield log({ kind: "hir", name: "MergeConsecutiveBlocks", value: hir });
 
   validateConsistentIdentifiers(hir);
+  validateTerminalSuccessors(hir);
 
   enterSSA(hir);
   yield log({ kind: "hir", name: "SSA", value: hir });

compiler/forget/src/HIR/ValidateTerminalSuccessors.ts

@@ -0,0 +1,27 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import { CompilerError } from "../CompilerError";
+import { GeneratedSource, HIRFunction } from "./HIR";
+import { printTerminal } from "./PrintHIR";
+import { mapTerminalSuccessors } from "./visitors";
+
+export function validateTerminalSuccessors(fn: HIRFunction): void {
+  for (const [, block] of fn.body.blocks) {
+    mapTerminalSuccessors(block.terminal, (successor) => {
+      if (!fn.body.blocks.has(successor)) {
+        CompilerError.invariant(
+          `Block bb${successor} does not exist for terminal '${printTerminal(
+            block.terminal
+          )}'`,
+          (block.terminal as any).loc ?? GeneratedSource
+        );
+      }
+      return successor;
+    });
+  }
+}

compiler/forget/src/HIR/index.ts

@@ -17,3 +17,5 @@ export {
 } from "./HIRBuilder";
 export { mergeConsecutiveBlocks } from "./MergeConsecutiveBlocks";
 export { printFunction, printHIR } from "./PrintHIR";
+export { validateConsistentIdentifiers } from "./ValidateConsistentIdentifiers";
+export { validateTerminalSuccessors } from "./ValidateTerminalSuccessors";

compiler/forget/src/Optimization/ConstantPropagation.ts

@@ -21,6 +21,8 @@ import {
   removeUnreachableFallthroughs,
   reversePostorderBlocks,
   shrink,
+  validateConsistentIdentifiers,
+  validateTerminalSuccessors,
 } from "../HIR";
 import { removeDeadDoWhileStatements } from "../HIR/HIRBuilder";
 import { eliminateRedundantPhi } from "../SSA";
@@ -70,6 +72,9 @@ export function constantPropagation(fn: HIRFunction): void {
     // Finally, merge together any blocks that are now guaranteed to execute
     // consecutively
     mergeConsecutiveBlocks(fn);
+
+    validateConsistentIdentifiers(fn);
+    validateTerminalSuccessors(fn);
   }
 }
 

compiler/forget/src/__tests__/fixtures/compiler/error.for-return.expect.md

@@ -0,0 +1,20 @@
+
+## Input
+
+```javascript
+function Component(props) {
+  for (let i = 0; i < props.count; i++) {
+    return;
+  }
+}
+
+```
+
+
+## Error
+
+```
+[ReactForget] Invariant: Block bb4 does not exist for terminal '[1] For init=bb3 test=bb1 loop=bb5 update=bb4 fallthrough=bb2' (2:4)
+```
+          
+      

compiler/forget/src/__tests__/fixtures/compiler/error.for-return.js

@@ -0,0 +1,5 @@
+function Component(props) {
+  for (let i = 0; i < props.count; i++) {
+    return;
+  }
+}