llv8-inl.h: Fix crash on sliced external strings (#123)

Sliced strings with an external string as a parent would use their offset
and length values against the string "(external)" as support for external
strings is not implemented yet.

Fixes: #112
PR-URL: #123
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

Author: hhellyer

src/llv8-inl.h

@@ -318,6 +318,13 @@ inline std::string SlicedString::ToString(Error& err) {
   String parent = Parent(err);
   if (err.Fail()) return std::string();
 
+  // TODO - Remove when we add support for external strings
+  // We can't use the offset and length safely if we get "(external)"
+  // instead of the original parent string.
+  if (parent.Representation(err) == v8()->string()->kExternalStringTag) {
+    return parent.ToString(err);
+  }
+
   Smi offset = Offset(err);
   if (err.Fail()) return std::string();
 

test/common.js

@@ -120,6 +120,7 @@ function Session(scenario) {
     '--',
     process.execPath,
     '--abort_on_uncaught_exception',
+    '--expose_externalize_string',
     path.join(exports.fixturesDir, scenario)
   ], {
     stdio: [ 'pipe', 'pipe', 'pipe' ],

test/fixtures/inspect-scenario.js

@@ -38,6 +38,15 @@ function closure() {
   c.hashmap['internalized-string'] = 'foobar';
   // This thin string points to the previous 'foobar'.
   c.hashmap['thin-string'] = makeThin('foo', 'bar');
+  // Create an externalized string and slice it.
+  c.hashmap['externalized-string'] =
+      'string that will be externalized and sliced';
+  externalizeString(c.hashmap['externalized-string']);
+  // Sliced strings need to be longer that SlicedString::kMinLength
+  // which seems to be 13 so our string is 26.
+  c.hashmap['sliced-externalized-string'] =
+      c.hashmap['externalized-string'].substring(10,36);
+
   c.hashmap['array'] = [true, 1, undefined, null, 'test', Class];
   c.hashmap['long-array'] = new Array(20).fill(5);
   c.hashmap['array-buffer'] = new Uint8Array(

test/inspect-test.js

@@ -48,6 +48,8 @@ tape('v8 inspect', (t) => {
   let regexp = null;
   let cons = null;
   let thin = null;
+  let ext = null;
+  let extSliced = null;
   let arrowFunc = null;
   let array = null;
   let longArray = null;
@@ -118,6 +120,17 @@ tape('v8 inspect', (t) => {
     t.ok(thinMatch, '.thin-string ThinString property');
     thin = thinMatch[1];
 
+    const extMatch = lines.match(
+        /.externalized-string=(0x[0-9a-f]+):<String: "\(external\)">/);
+    t.ok(extMatch, '.externalized-string ExternalString property');
+    ext = extMatch[1];
+
+    const extSlicedMatch = lines.match(
+        /.sliced-externalized-string=(0x[0-9a-f]+):<String: "\(external\)">/);
+    t.ok(extSlicedMatch,
+         '.sliced-externalized-string Sliced ExternalString property');
+    extSliced = extSlicedMatch[1];
+
     sess.send(`v8 inspect ${regexp}`);
     sess.send(`v8 inspect -F ${cons}`);
   });