Learning VS Code source
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Created: May 26, 2018 / Updated: November 2, 2024 / Status: draft / 7 min read (~1305 words)
Created: May 26, 2018 / Updated: November 2, 2024 / Status: draft / 7 min read (~1305 words)
- Read
package.json
to discover what packages VS Code depends on - Observe the root directory structure, and more specifically the
extensions
andsrc
directories which contain the bulk of the source code- A lot of the code in the
extensions
directory appears to be dedicated to programming language support- The remainder of the extensions seem to provide functionality for things that aren't "core" to vscode, such as
configuration-editing
,emmet
,extension-editing
and some color themes
- The remainder of the extensions seem to provide functionality for things that aren't "core" to vscode, such as
- A lot of the code in the
- If you look at the
.vscode/launch.json
, you will find all the tasks that can be executed from within VS Code debugger. One task of interest isLaunch VS Code
which will take care of launching VS Code for us so that we may debug it- In this file you will also discover that it runs
${workspaceFolder}/scripts/code.bat
, which is the next script we'll take a look at
- In this file you will also discover that it runs
- In
./scripts/code.bat
, we discover that this script will runyarn
if thenode_modules
directory is missing, download the electron binaries if necessary and callgulp compile
if theout
directory is missing, then finally start the electron/vs code binary in the.build/electron
directory - We then start to look for common entry points file such as
index.ts/js
ormain.ts/js
, for which we find a match in thesrc
directory - We take a quick look around, trying to find where electron is likely to be instantiated... There's a lot of code in
src/main.js
that would be better elsewhere to make it easier to navigate this file - Close to the bottom of the file we discover the code we are interested in as a call to
app.once('ready', ...)
- Once the app is ready, we want to call
src/bootstrap-amd
and passvs/code/electron-main/main
as our entry point (per the signature of the exported function in./src/bootstrap-amd
)- Here we can go to two places, either
src/bootstrap-amd
orsrc/vs/code/electron-main/main
- We take a quick peek at both files and we can quickly tell that
src/bootstrap-amd
is used mainly to loadsrc/vs/code/electron-main/main
which is the file we're going to be interested in
- We take a quick peek at both files and we can quickly tell that
- Here we can go to two places, either
- Once the app is ready, we want to call
- Once again, we quickly look around
src/vs/code/electron-main/main
and find that the main logic is at the bottom of the file - First the command line arguments are parsed
- Then services are bootstrapped/instantiated
- Finally the
CodeApplication
is started up - This leads us to look into
src/vs/code/electron-main/app.ts
- As the file is quite large, we start by skimming through it, looking at the available methods on the
CodeApplication
class as well as its properties - Looking at the constructor, we can see that a lot of objects are given to it. We also observe the use of the @... syntax (those are decorators)
- In this case (and for most constructors), this is how VS Code does service (dependencies) injection
-
One will also notice that most, if not all parameters have a visibility assigned to it. What this does is that it will create an associated property in the class as well as assigning the parameter value to this property in the constructor. Thus, instead of writing
class AnotherClass { private someClass: SomeClass; constructor(someClass: SomeClass) { this.someClass = someClass; } }
you simply write
class AnotherClass { constructor(private someClass: SomeClass) { } }
- Upon its creation, the
CodeApplication
class will register various event listeners on the electron app object - If we remember, in
src/vs/code/electron-main/main
, after theCodeApplication
object is instantiated, we callstartup()
on it. So, we want to take a look at what that method does - Without knowing too much about the VS Code source, it appears that we are instantiating an IPC server (inter-process communication) and then the shared process
- After that is done, we initialize some more services in
CodeApplication::initServices
, such as the update service (which I guess takes care of checking for VS Code updates) and the telemetry (data about VS Code feature usage) - We finally get to the point where we're about to open a window in
CodeApplication::openFirstWindow
!- This leads us to go read the class
WindowsManager
insrc/vs/code/electron-main/windows.ts
. Once again, this file is pretty large, so we want to skim it to see what it contains (functions, classes, properties, methods)
- This leads us to go read the class
- There are a few large classes in
src/vs/code/electron-main/windows.ts
that I'd want to extract to make the file smaller and simpler (less cognitive load). However, the issue is that those classes are not declared as exported, and thus are only available in the local file. It would be possible to move these classes to other files and import them, but by doing so it would also "communicate" that others can use it, which is what having the classes as not exported prevents, at the cost of making single files larger and harder to comprehend - We know that the constructor is first called, then from
CodeApplication::openFirstWindow
, we see thatWindowsManager::ready
andWindowsManager::open
are both called.- In the
constructor
we instantiate theDialogs
class (takes care of open/save dialog windows) and theWorkspacesManager
class (takes care of workspace management, such as open/save) - In
ready
event listeners are registered - In
open
there is a lot of logic associated with the window finally opening
- In the
- If you start VS Code using the debug feature, you will not be able to open the Chrome DevTools (at this moment, 2018-05-26) because only 1 process is allowed to attach to the Chrome DevTools instance, and that process is the VS Code editor that started the debugged VS Code instance
Today I want to find out how VS Code restores a windows sessions when you start it. Apparently, if you run it as code .
, it will not restore the same set of windows than if you called it simply with code
.
- In
src/vs/code/electron-main/launch.ts
, theLaunchService::startOpenWindow
appears to implement logic based on how many arguments were given. In all cases, we end up doing a call to theIWindowsMainService::open
method.- Note that in both cases, the path we're opening is within the
args
variable, which is passed to thecli
property of theIOpenConfiguration
object.
- Note that in both cases, the path we're opening is within the
- The implementation of
IWindowsMainService
we are interested in lives insrc/vs/code/electron-main/windows.ts
. - In the
WindowsManager::open
method, we rapidly discover that the windows that will be opened will be retrieved inWindowsManager::getPathsToOpen
. In there, we can observe that the windows that will be opened depend on whether something was passed from the API, we forced an empty window, we're extracting paths from the cli or we should restore from the previous session.- If we arrive at this last case, we can see that the logic is to call
WindowsManager::doGetWindowsFromLastSession
, which is pretty self-explanatory, and will retrieve the previous set of windows from the last session. This is what happens when you startcode
usingcode
- In the case where we pass a path, this path is in
openConfig.cli._
. In this case, the windows that were previously opened, and part ofthis.windowsState.openedWindows
(wherethis
is aWindowsManager
object)- Here we wonder how the
windowsState.openedWindows
state gets restored on VS Code start. To figure that out, we start at theWindowsManager.constructor
method. There we findthis.windowsState = this.stateService.getItem<IWindowsState>(WindowsManager.windowsStateStorageKey) || { openedWindows: [] };
, which states to use get aIWindowState
object from thestateService
if one exists or to create an object with no opened windows. If we assume that this windows state is the same regardless of how we start VS Code, then it is not there that the difference in opened windows will occur.
- Here we wonder how the
- If we arrive at this last case, we can see that the logic is to call