Fix misaligned lines in debugger #634

filip131311 · 2024-10-16T20:11:15Z

This PR fixes a problem with debugger on expo projects, caused by prelude lines added to the entry bundle file added by expo. The solution is t0 add the required offset to the prelude causing the problem and scanning for it when receiving source map in the debuger.

It is possible that the changes will no longer be needed in future versions of react native as the expo team tries to correct source map generation to include extra lines, for more information read those PRs:

This is why we add version check before adding lineOffset to initial source map.

How Has This Been Tested:

open expo project and set a breakpoint, before the changes it would trigger 2 lines above the place it's been set.
save any change in the file containing breakpoint and make sure it still works.
check if links to files generated next to console logs are pointing in to the correct place, again both before and after making changes to the file.
check if error position indicator (when uncaught exception is raised) points to the correct position.

Additional changes:

This PR also fixes a minor mistake with getReactNativeVersion utility that does not need to be async and as it is used, we make it synchronous as part of this PR.

vercel · 2024-10-16T20:11:40Z

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kmagiera

I don't like the coupling between console calls that are also meant to provide the offset and the source map parser that seems to expect the console call prior to the "source maps ready" call.

I think we should instead restructure it in the following way:

Remove __EXPO_ENV_PRELUDE_LINES__ entirely
Instead of it, we should log a command from metro process that will be captured by line reader. Similarily to how we do with RNIDE_initialize_done, but it will also contain the offset number
Read the offset in metro.ts using line reader and expose it such that we can provide it as a parameter to the debug session

packages/vscode-extension/src/debugging/DebugAdapter.ts

filip131311 · 2024-10-17T10:21:39Z

@kmagiera you were right, I changed it according to your suggestions.

kmagiera · 2024-10-17T11:23:47Z

packages/vscode-extension/lib/metro_helpers.js

- module.output[0].data.code = `${expoEnvCode};var __EXPO_ENV_PRELUDE_LINES__=${module.output[0].data.lineCount};`;
- }
+ const expoEnvPreludeLines = module.output[0].data.lineCount;
+ process.stdout.write(JSON.stringify({ type: "RNIDE_Expo_Env_Prelude_Lines", expoEnvPreludeLines }));


For consistency with RNIDE_initialize_done I wouldn't use capitalized words here

kmagiera · 2024-10-17T11:27:39Z

packages/vscode-extension/src/project/metro.ts

@@ -64,6 +68,7 @@ type MetroEvent =
 export class Metro implements Disposable {
 private subprocess?: ChildProcess;
 private _port = 0;
+ private _initialBundleLineOffset = 0;


I don't like "initial" word here as it isn't accurate. I think the offset applies for the whole bundle not just for the first bundle that gets loaded as it is currently implemented.

We should rename "mainBundleLineOffset"

packages/vscode-extension/src/debugging/DebugAdapter.ts

kmagiera · 2024-10-17T15:33:23Z

I'm now thinking that it may actually be the easiest solution to still include the offset in the bundle, and when we get source map we'd check if the offset variable exists there and read its value. If this would work, that'd be the best solution in my option. The only reason why it may not work is that I'm not sure if the preamble actually gets included in the source map at all. Tthe reason we're adding this offset was that there was an issue with that. But, perhaps, the issue was only because it is considered to have 0 length rather than just being completely omitted. You'll need to check the bundle for that to tell

kmagiera

Left a few more comments inline, but since only related to variable/parameter names and comments I'm accepting, as otherwise the code looks good.
The only comment that may require more attention is about whether we should test agains expo or react native version when determining when to use offset parameter and when not

kmagiera · 2024-10-21T22:28:37Z

packages/vscode-extension/src/debugging/DebugAdapter.ts

+
+ // This is a heuristic that checks if the source map should contain __env__
+ // module that is added by expo, but not reported in the source map
+ const isFileWithOffset = sourceMap.sources.includes("__prelude__");


rename isMainBundle or isFullBundle

kmagiera · 2024-10-21T22:31:27Z

packages/vscode-extension/src/debugging/DebugAdapter.ts

+ // This is a heuristic that checks if the source map should contain __env__
+ // module that is added by expo, but not reported in the source map


Suggested change

// This is a heuristic that checks if the source map should contain __env__

// module that is added by expo, but not reported in the source map

// We detect when a source map for the entire bundle is loaded by checking

// if __env__ module is present in the sources.

kmagiera · 2024-10-21T22:34:22Z

packages/vscode-extension/src/debugging/DebugAdapter.ts

@@ -96,6 +98,7 @@ export class DebugAdapter extends DebugSession {
 this.absoluteProjectPath = configuration.absoluteProjectPath;
 this.projectPathAlias = configuration.projectPathAlias;
 this.connection = new WebSocket(configuration.websocketAddress);
+ this.lineOffset = configuration.lineOffset;


This parameter should really be called expoPreludeExtraLines or something along these lines instead of being so generic

kmagiera · 2024-10-21T22:35:00Z

packages/vscode-extension/src/debugging/DebugAdapter.ts

+ // https://github.com/facebook/metro/pull/1284 we should monitor the situation
+ // in upcoming versions and if the changes are still not added bump the version below.
+ const shouldApplyOffset =
+ semver.lte(getReactNativeVersion(), "0.76.0") && isFileWithOffset;


should we check for expo version here and not react native?

kmagiera · 2024-10-21T22:37:58Z

packages/vscode-extension/src/debugging/DebugAdapter.ts

+ // This line is here because of a problem with sourcemaps for expo projects,
+ // that was addressed in this PR https://github.com/expo/expo/pull/29463,
+ // unfortunately it still requires changes to metro that were attempted here
+ // https://github.com/facebook/metro/pull/1284 we should monitor the situation
+ // in upcoming versions and if the changes are still not added bump the version below.


Suggested change

// This line is here because of a problem with sourcemaps for expo projects,

// that was addressed in this PR https://github.com/expo/expo/pull/29463,

// unfortunately it still requires changes to metro that were attempted here

// https://github.com/facebook/metro/pull/1284 we should monitor the situation

// in upcoming versions and if the changes are still not added bump the version below.

// When using expo <${PUT_VERSION_HERE}, source maps skip the prelude module which is

// included in the main bundle at the start. As a result, all lines in the main bundle are shifted by

// the amount of lines the prelude file adds. To offset this, we use the lineOffset parameter that we pass

// to the source maps list that is used later on to correct line numbers when translating from generated

// to the original positions.

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move to passing informatoion througsh metro

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Fix misaligned lines in debugger #634

Fix misaligned lines in debugger #634

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		// This is a heuristic that checks if the source map should contain __env__
		// module that is added by expo, but not reported in the source map

Fix misaligned lines in debugger #634

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Fix misaligned lines in debugger #634

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How Has This Been Tested:

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