Add evaluateWithPossibleThrowCompletion

I'm going to need to add a lot of these things that might throw so I wanted
to start preparing the infrastructure for fixing facebookarchive#1264.

The idea is that code inside this scope might emit temporal operations that
might throw. In the future we can wrap these in a try/catch to extract a
caught error and a flag. These can be used to generate a
PossiblyNormalCompletion.

However, for now I just keep the existing strategy of erroring in this case
while I add more callers of this helper.

src/evaluators/CallExpression.js

@@ -14,6 +14,7 @@ import { AbruptCompletion, PossiblyNormalCompletion } from "../completions.js";
 import type { Realm } from "../realm.js";
 import type { LexicalEnvironment } from "../environment.js";
 import { EnvironmentRecord } from "../environment.js";
+import { TypesDomain, ValuesDomain } from "../domains/index.js";
 import { Value } from "../values/index.js";
 import { AbstractValue, BooleanValue, ConcreteValue, FunctionValue } from "../values/index.js";
 import { Reference } from "../environment.js";
@@ -139,8 +140,7 @@ function EvaluateCall(
     if (!Value.isTypeCompatibleWith(func.getType(), FunctionValue)) {
       if (!realm.isInPureScope()) {
         // If this is not a function, this call might throw which can change the state of the program.
-        // If this is called from a pure function it is safe, unless in a try/catch which has a
-        // separate error below.
+        // If this is called from a pure function we handle it using evaluateWithPossiblyAbruptCompletion.
         let error = new CompilerDiagnostic("might not be a function", loc, "PP0005", "RecoverableError");
         if (realm.handleError(error) === "Fail") throw new FatalError();
       }
@@ -149,16 +149,9 @@ function EvaluateCall(
     } else {
       // Assume that it is a safe function. TODO #705: really?
     }
-    if (realm.isInPureTryStatement) {
-      // TODO(1264): We should be able to preserve error handling on abstract throw
-      // but currently we just issue a recoverable error instead.
-      let diag = new CompilerDiagnostic(
-        "Possibly throwing function call inside try/catch",
-        loc,
-        "PP0021",
-        "RecoverableError"
-      );
-      if (realm.handleError(diag) !== "Recover") throw new FatalError();
+    if (realm.isInPureScope()) {
+      // In pure functions we allow abstract functions to throw, which this might.
+      return realm.evaluateWithPossibleThrowCompletion(generateRuntimeCall, TypesDomain.topVal, ValuesDomain.topVal);
     }
     return generateRuntimeCall();
   }

src/realm.js

@@ -25,6 +25,7 @@ import {
   UndefinedValue,
   Value,
 } from "./values/index.js";
+import type { TypesDomain, ValuesDomain } from "./domains/index.js";
 import { LexicalEnvironment, Reference, GlobalEnvironmentRecord, DeclarativeEnvironmentRecord } from "./environment.js";
 import type { Binding } from "./environment.js";
 import { cloneDescriptor, Construct } from "./methods/index.js";
@@ -427,6 +428,33 @@ export class Realm {
     return !!this.createdObjectsTrackedForLeaks;
   }
 
+  // Evaluate some code that might generate temporal values knowing that it might end in an abrupt
+  // completion. We only need to support ThrowCompletion for now but this can be expanded to support other
+  // abrupt completions.
+  evaluateWithPossibleThrowCompletion(f: () => Value, thrownTypes: TypesDomain, thrownValues: ValuesDomain): Value {
+    // The cases when we need this are only when we might invoke unknown code such as abstract
+    // funtions, getters, custom coercion etc. It is possible we can use this in other cases
+    // where something might throw a built-in error but can never issue arbitrary code such as
+    // calling something that might not be a function. For now we only use it in pure functions.
+    invariant(this.isInPureScope(), "only abstract abrupt completion in pure functions");
+
+    // TODO(1264): We should create a new generator for this scope and wrap it in a try/catch.
+    // We could use the outcome of that as the join condition for a PossiblyNormalCompletion.
+    // We should then compose that with the saved completion and move on to the normal route.
+    // Currently we just issue a recoverable error instead if this might matter.
+    let value = f();
+    if (this.isInPureTryStatement) {
+      let diag = new CompilerDiagnostic(
+        "Possible throw inside try/catch is not yet supported",
+        this.currentLocation,
+        "PP0021",
+        "RecoverableError"
+      );
+      if (this.handleError(diag) !== "Recover") throw new FatalError();
+    }
+    return value;
+  }
+
   // Evaluate the given ast in a sandbox and return the evaluation results
   // in the form of a completion, a code generator, a map of changed variable
   // bindings and a map of changed property bindings.

src/values/AbstractObjectValue.js

@@ -9,7 +9,7 @@
 
 /* @flow */
 
-import { CompilerDiagnostic, FatalError } from "../errors.js";
+import { FatalError } from "../errors.js";
 import type { Realm } from "../realm.js";
 import type { Descriptor, PropertyKeyValue } from "../types.js";
 import { AbstractValue, ArrayValue, ObjectValue, StringValue, Value } from "./index.js";
@@ -313,22 +313,7 @@ export default class AbstractObjectValue extends AbstractValue {
   $Get(P: PropertyKeyValue, Receiver: Value): Value {
     if (P instanceof StringValue) P = P.value;
     if (this.values.isTop()) {
-      if ((this.isSimpleObject() && this.isIntrinsic()) || this.$Realm.isInPureScope()) {
-        if (!this.isSimpleObject()) {
-          if (this.$Realm.isInPureTryStatement) {
-            // TODO(1264): We should be able to preserve error handling on abstract throw
-            // but currently we just issue a recoverable error instead.
-            let diag = new CompilerDiagnostic(
-              "Possibly throwing getter inside try/catch",
-              this.$Realm.currentLocation,
-              "PP0021",
-              "RecoverableError"
-            );
-            if (this.$Realm.handleError(diag) !== "Recover") throw new FatalError();
-          }
-          // This object might have leaked to a getter.
-          Leak.leakValue(this.$Realm, this);
-        }
+      let generateAbstractGet = () => {
         let type = Value;
         if (P === "length" && Value.isTypeCompatibleWith(this.getType(), ArrayValue)) type = NumberValue;
         let object = this.kind === "sentinel ToObject" ? this.args[0] : this;
@@ -344,6 +329,18 @@ export default class AbstractObjectValue extends AbstractValue {
             skipInvariant: true,
           }
         );
+      };
+      if (this.isSimpleObject() && this.isIntrinsic()) {
+        return generateAbstractGet();
+      } else if (this.$Realm.isInPureScope()) {
+        // This object might have leaked to a getter.
+        Leak.leakValue(this.$Realm, this);
+        // The getter might throw anything.
+        return this.$Realm.evaluateWithPossibleThrowCompletion(
+          generateAbstractGet,
+          TypesDomain.topVal,
+          ValuesDomain.topVal
+        );
       }
       AbstractValue.reportIntrospectionError(this, P);
       throw new FatalError();

test/error-handler/try-and-access-abstract-property.js

@@ -1,7 +1,7 @@
 // additional functions
 // abstract effects
 // recover-from-errors
-// expected errors: [{location: {"start":{"line":14,"column":11},"end":{"line":14,"column":15},"identifierName":"obj1","source":"test/error-handler/try-and-access-abstract-property.js"}, errorCode: "PP0021", severity: "RecoverableError", message: "Possibly throwing getter inside try/catch"},{location: {"start":{"line":22,"column":11},"end":{"line":22,"column":15},"identifierName":"obj2","source":"test/error-handler/try-and-access-abstract-property.js"}, errorCode: "PP0021", severity: "RecoverableError", message: "Possibly throwing getter inside try/catch"}]
+// expected errors: [{location: {"start":{"line":14,"column":11},"end":{"line":14,"column":15},"identifierName":"obj1","source":"test/error-handler/try-and-access-abstract-property.js"}, errorCode: "PP0021", severity: "RecoverableError", message: "Possible throw inside try/catch is not yet supported"},{location: {"start":{"line":22,"column":11},"end":{"line":22,"column":15},"identifierName":"obj2","source":"test/error-handler/try-and-access-abstract-property.js"}, errorCode: "PP0021", severity: "RecoverableError", message: "Possible throw inside try/catch is not yet supported"}]
 
 let obj1 = global.__abstract ? __abstract('object', '({get foo() { return "bar"; }})') : {get foo() { return "bar"; }};
 let obj2 = global.__abstract ? __abstract('object', '({foo:{bar:"baz"}})') : {foo:{bar:"baz"}};

test/error-handler/try-and-call-abstract-function.js

@@ -1,6 +1,6 @@
 // additional functions
 // abstract effects
-// expected errors: [{location: {"start":{"line":26,"column":11},"end":{"line":26,"column":21},"identifierName":"abstractFn","source":"test/error-handler/try-and-call-abstract-function.js"}, errorCode: "PP0021", severity: "RecoverableError", message: "Possibly throwing function call inside try/catch"}]
+// expected errors: [{location: {"start":{"line":26,"column":11},"end":{"line":26,"column":21},"identifierName":"abstractFn","source":"test/error-handler/try-and-call-abstract-function.js"}, errorCode: "PP0021", severity: "RecoverableError", message: "Possible throw inside try/catch is not yet supported"}]
 
 let abstractFn = global.__abstract ? __abstract('function', '(function() { return true; })') : function() { return true; };