[compiler] source location validator (facebook#35109)

@josephsavona this was briefly discussed in an old thread, lmk your
thoughts on the approach. I have some fixes ready as well but wanted to
get this test case in first... there's some things I don't _love_ about
this approach, but end of the day it's just a tool for the test suite
rather than something for end user folks so even if it does a 70% good
enough job that's fine.

### refresher on the problem
when we generate coverage reports with jest (istanbul), our coverage
ends up completely out of whack due to the AST missing a ton of (let's
call them "important") source locations after the compiler pipeline has
run.

At the moment to get around this, we've been doing something a bit
unorthodox and also running our test suite with istanbul running before
the compiler -- which results in its own set of issues (for eg, things
being memoized differently, or the compiler completely bailing out on
the instrumented code, etc).

before getting in fixes, I wanted to set up a test case to start
chipping away on as you had recommended.

### how it works

The validator basically:
1. Traverses the original AST and collects the source locations for some
"important" node types
- (excludes useMemo/useCallback calls, as those are stripped out by the
compiler)
3. Traverses the generated AST and looks for nodes with matching source
locations.
4. Generates errors for source locations missing nodes in the generated
AST

### caveats/drawbacks

There are some things that don't work super well with this approach. A
more natural test fit I think would be just having some explicit
assertions made against an AST in a test file, as you can just bake all
of the assumptions/nuance in there that are difficult to handle in a
generic manner. However, this is maybe "good enough" for now.

1. Have to be careful what you put into the test fixture. If you put in
some code that the compiler just removes (for eg, a variable assignment
that is unused), you're creating a failure case that's impossible to
fix. I added a skip for useMemo/useCallback.
2. "Important" locations must exactly match for validation to pass.
- Might get tricky making sure things are mapped correctly when a node
type is completely changed, for eg, when a block statement arrow
function body gets turned into an implicit return via the body just
being an expression/identifier.
- This can/could result in scenarios where more changes are needed to
shuttle the locations through due to HIR not having a 1:1 mapping all
the babel nuances, even if some combination of other data might be good
enough even if not 10000% accurate. This might be the _right_ thing
anyways so we don't end up with edge cases having incorrect source
locations.

DiffTrain build for [3a495ae](facebook@3a495ae)

Author: pull[bot]

compiled/eslint-plugin-react-hooks/index.js

@@ -32166,6 +32166,7 @@ const EnvironmentConfigSchema = v4.z.object({
     validateMemoizedEffectDependencies: v4.z.boolean().default(false),
     validateNoCapitalizedCalls: v4.z.nullable(v4.z.array(v4.z.string())).default(null),
     validateBlocklistedImports: v4.z.nullable(v4.z.array(v4.z.string())).default(null),
+    validateSourceLocations: v4.z.boolean().default(false),
     validateNoImpureFunctionsInRender: v4.z.boolean().default(false),
     validateNoFreezingKnownMutableFunctions: v4.z.boolean().default(false),
     enableAssumeHooksFollowRulesOfReact: v4.z.boolean().default(true),
@@ -50318,6 +50319,116 @@ function isUnmemoized(operand, scopes) {
     return operand.scope != null && !scopes.has(operand.scope.id);
 }
 
+const IMPORTANT_INSTRUMENTED_TYPES = new Set([
+    'ArrowFunctionExpression',
+    'AssignmentPattern',
+    'ObjectMethod',
+    'ExpressionStatement',
+    'BreakStatement',
+    'ContinueStatement',
+    'ReturnStatement',
+    'ThrowStatement',
+    'TryStatement',
+    'VariableDeclarator',
+    'IfStatement',
+    'ForStatement',
+    'ForInStatement',
+    'ForOfStatement',
+    'WhileStatement',
+    'DoWhileStatement',
+    'SwitchStatement',
+    'SwitchCase',
+    'WithStatement',
+    'FunctionDeclaration',
+    'FunctionExpression',
+    'LabeledStatement',
+    'ConditionalExpression',
+    'LogicalExpression',
+]);
+function isManualMemoization(node) {
+    if (libExports$1.isCallExpression(node)) {
+        const callee = node.callee;
+        if (libExports$1.isIdentifier(callee)) {
+            return callee.name === 'useMemo' || callee.name === 'useCallback';
+        }
+        if (libExports$1.isMemberExpression(callee) &&
+            libExports$1.isIdentifier(callee.property) &&
+            libExports$1.isIdentifier(callee.object)) {
+            return (callee.object.name === 'React' &&
+                (callee.property.name === 'useMemo' ||
+                    callee.property.name === 'useCallback'));
+        }
+    }
+    return false;
+}
+function locationKey(loc) {
+    return `${loc.start.line}:${loc.start.column}-${loc.end.line}:${loc.end.column}`;
+}
+function validateSourceLocations(func, generatedAst) {
+    const errors = new CompilerError();
+    const importantOriginalLocations = new Map();
+    func.traverse({
+        enter(path) {
+            const node = path.node;
+            if (!IMPORTANT_INSTRUMENTED_TYPES.has(node.type)) {
+                return;
+            }
+            if (isManualMemoization(node)) {
+                return;
+            }
+            if (node.loc) {
+                const key = locationKey(node.loc);
+                importantOriginalLocations.set(key, {
+                    loc: node.loc,
+                    nodeType: node.type,
+                });
+            }
+        },
+    });
+    const generatedLocations = new Set();
+    function collectGeneratedLocations(node) {
+        if (node.loc) {
+            generatedLocations.add(locationKey(node.loc));
+        }
+        const keys = libExports$1.VISITOR_KEYS[node.type];
+        if (!keys) {
+            return;
+        }
+        for (const key of keys) {
+            const value = node[key];
+            if (Array.isArray(value)) {
+                for (const item of value) {
+                    if (libExports$1.isNode(item)) {
+                        collectGeneratedLocations(item);
+                    }
+                }
+            }
+            else if (libExports$1.isNode(value)) {
+                collectGeneratedLocations(value);
+            }
+        }
+    }
+    collectGeneratedLocations(generatedAst.body);
+    for (const outlined of generatedAst.outlined) {
+        collectGeneratedLocations(outlined.fn.body);
+    }
+    for (const [key, { loc, nodeType }] of importantOriginalLocations) {
+        if (!generatedLocations.has(key)) {
+            errors.pushDiagnostic(CompilerDiagnostic.create({
+                category: ErrorCategory.Todo,
+                reason: 'Important source location missing in generated code',
+                description: `Source location for ${nodeType} is missing in the generated output. This can cause coverage instrumentation ` +
+                    `to fail to track this code properly, resulting in inaccurate coverage reports.`,
+            }).withDetails({
+                kind: 'error',
+                loc,
+                message: null,
+            }));
+        }
+    }
+    return errors.asResult();
+}
+
 function validateUseMemo(fn) {
     const errors = new CompilerError();
     const voidMemoErrors = new CompilerError();
@@ -53201,6 +53312,9 @@ function runWithEnvironment(func, env) {
     for (const outlined of ast.outlined) {
         log({ kind: 'ast', name: 'Codegen (outlined)', value: outlined.fn });
     }
+    if (env.config.validateSourceLocations) {
+        validateSourceLocations(func, ast).unwrap();
+    }
     if (env.config.throwUnknownException__testonly) {
         throw new Error('unexpected error');
     }

compiled/facebook-www/REVISION

@@ -1 +1 @@
-bbe3f4d322846083c57009dbd6121900f120b389
+3a495ae72264c46b4a4355904c6b4958b0a2f9b2

compiled/facebook-www/REVISION_TRANSFORMS

@@ -1 +1 @@
-bbe3f4d322846083c57009dbd6121900f120b389
+3a495ae72264c46b4a4355904c6b4958b0a2f9b2

compiled/facebook-www/React-dev.classic.js

@@ -1499,7 +1499,7 @@ __DEV__ &&
     exports.useTransition = function () {
       return resolveDispatcher().useTransition();
     };
-    exports.version = "19.3.0-www-classic-bbe3f4d3-20251112";
+    exports.version = "19.3.0-www-classic-3a495ae7-20251112";
     "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
       "function" ===
         typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&

compiled/facebook-www/React-dev.modern.js

@@ -1499,7 +1499,7 @@ __DEV__ &&
     exports.useTransition = function () {
       return resolveDispatcher().useTransition();
     };
-    exports.version = "19.3.0-www-modern-bbe3f4d3-20251112";
+    exports.version = "19.3.0-www-modern-3a495ae7-20251112";
     "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
       "function" ===
         typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&

compiled/facebook-www/React-prod.classic.js

@@ -606,4 +606,4 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactSharedInternals.H.useTransition();
 };
-exports.version = "19.3.0-www-classic-bbe3f4d3-20251112";
+exports.version = "19.3.0-www-classic-3a495ae7-20251112";

compiled/facebook-www/React-prod.modern.js

@@ -606,4 +606,4 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactSharedInternals.H.useTransition();
 };
-exports.version = "19.3.0-www-modern-bbe3f4d3-20251112";
+exports.version = "19.3.0-www-modern-3a495ae7-20251112";

compiled/facebook-www/React-profiling.classic.js

@@ -610,7 +610,7 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactSharedInternals.H.useTransition();
 };
-exports.version = "19.3.0-www-classic-bbe3f4d3-20251112";
+exports.version = "19.3.0-www-classic-3a495ae7-20251112";
 "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
   "function" ===
     typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&

compiled/facebook-www/React-profiling.modern.js

@@ -610,7 +610,7 @@ exports.useSyncExternalStore = function (
 exports.useTransition = function () {
   return ReactSharedInternals.H.useTransition();
 };
-exports.version = "19.3.0-www-modern-bbe3f4d3-20251112";
+exports.version = "19.3.0-www-modern-3a495ae7-20251112";
 "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
   "function" ===
     typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&

compiled/facebook-www/ReactART-dev.classic.js

@@ -20466,10 +20466,10 @@ __DEV__ &&
     (function () {
       var internals = {
         bundleType: 1,
-        version: "19.3.0-www-classic-bbe3f4d3-20251112",
+        version: "19.3.0-www-classic-3a495ae7-20251112",
         rendererPackageName: "react-art",
         currentDispatcherRef: ReactSharedInternals,
-        reconcilerVersion: "19.3.0-www-classic-bbe3f4d3-20251112"
+        reconcilerVersion: "19.3.0-www-classic-3a495ae7-20251112"
       };
       internals.overrideHookState = overrideHookState;
       internals.overrideHookStateDeletePath = overrideHookStateDeletePath;
@@ -20504,7 +20504,7 @@ __DEV__ &&
     exports.Shape = Shape;
     exports.Surface = Surface;
     exports.Text = Text;
-    exports.version = "19.3.0-www-classic-bbe3f4d3-20251112";
+    exports.version = "19.3.0-www-classic-3a495ae7-20251112";
     "undefined" !== typeof __REACT_DEVTOOLS_GLOBAL_HOOK__ &&
       "function" ===
         typeof __REACT_DEVTOOLS_GLOBAL_HOOK__.registerInternalModuleStop &&