lib: account for cwd access from snapshot serialization cb

Functions registered with `addSerializeCallback()` can access and call
`process.cwd()`. b7d836e accounted for the fact that it is
necessary to reset the cwd cache after the snapshot builder script has
run, but did not account for possible accesses from serialization
callbacks. To properly account for these, add a deserialization
callback as well.

As a related drive-by fix, also mention the execution order of
callbacks in the documentation.

Refs: nodejs#49684
PR-URL: nodejs#51901
Reviewed-By: Joyee Cheung <[email protected]>
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Marco Ippolito <[email protected]>

Author: addaleax

doc/api/v8.md

@@ -1021,6 +1021,8 @@ get serialized into a snapshot and exit. This can be used to release
 resources that should not or cannot be serialized or to convert user data
 into a form more suitable for serialization.
 
+Callbacks are run in the order in which they are added.
+
 ### `v8.startupSnapshot.addDeserializeCallback(callback[, data])`
 
 <!-- YAML
@@ -1040,6 +1042,8 @@ serialized into the snapshot, they can be used to re-initialize the state
 of the application or to re-acquire resources that the application needs
 when the application is restarted from the snapshot.
 
+Callbacks are run in the order in which they are added.
+
 ### `v8.startupSnapshot.setDeserializeMainFunction(callback[, data])`
 
 <!-- YAML

lib/internal/bootstrap/switches/does_own_process_state.js

@@ -4,6 +4,7 @@ const credentials = internalBinding('credentials');
 const rawMethods = internalBinding('process_methods');
 const {
   namespace: {
+    addDeserializeCallback,
     addSerializeCallback,
     isBuildingSnapshot,
   },
@@ -114,8 +115,13 @@ function wrapPosixCredentialSetters(credentials) {
 let cachedCwd = '';
 
 if (isBuildingSnapshot()) {
+  // Reset the cwd on both serialization and deserialization so it's fine
+  // for process.cwd() to be accessed inside of serialization callbacks.
   addSerializeCallback(() => {
     cachedCwd = '';
+    addDeserializeCallback(() => {
+      cachedCwd = '';
+    });
   });
 }
 

test/fixtures/snapshot/cwd.js

@@ -1,10 +1,16 @@
 const {
+  addSerializeCallback,
   setDeserializeMainFunction,
 } = require('v8').startupSnapshot;
 
 // To make sure the cwd is present in the cache
 process.cwd();
 
+// Also access it from a serialization callback once
+addSerializeCallback(() => {
+  process.cwd();
+});
+
 setDeserializeMainFunction(() => {
   console.log(process.cwd());
 });