Typescript watch compiles each edited file twice

[eladstr]

Bug Report

🔎 Search Terms

Typescript watch triggers multiple compilations

🕗 Version & Regression Information

This changed when moving from Typescript version 4.8.4 to 4.9.3

Reviewed: #37994

⏯ Demonstration Video

Screen.Recording.2022-11-21.at.12.46.08.mov

💻 Code

package.json

{
"name": "testtsc",
"version": "1.0.0",
"description": "Test double compilation of TypeScript files",
"main": "index.js",
"scripts": {
"test": "echo "Error: no test specified" && exit 1"
},
"author": "Elad Stern",
"license": "ISC",
"dependencies": {
"typescript": "^4.9.3"
}
}

main.ts

let a: string = "123456790123";
alert(a.slice(0, 2));

🙁 Actual behavior

In terminal, invoking npx and then tsc main.ts --watch, changing the source code of main.ts triggers Typescript watch to compile the file again - not once, but twice. The same took place in larger projects - double compilation of changed files, with one or two seconds in between.

🙂 Expected behavior

Once a source code file has been changed, it should compile only once by tsc watch, not twice.

[eladstr]

GIST link:
https://gist.github.com/eladstr/53a764cd35b2045635c0397eb59a804b

[sheetalkamat]

please post log with tsc --watch main.ts --extendedDiagnostics even though it looks like it has compiled twice the actual transformation should happen only once. It looks like on windows (which is where i tested) the file change event was generated twice which is why this behaviour.

[eladstr]

terminal output with --extendedDiagnostics:

sh-3.2$ tsc main.ts --watch --extendedDiagnostics
[10:18:14 AM] Starting compilation in watch mode...

Current directory: /Users/elads/Projects/testtsc CaseSensitiveFileNames: false
Synchronizing program
CreatingProgramWith::
roots: ["main.ts"]
options: {"watch":true,"extendedDiagnostics":true}
FileWatcher:: Added:: WatchInfo: main.ts 250 undefined Source file
FileWatcher:: Added:: WatchInfo: /Users/elads/Projects/testtsc/node_modules/typescript/lib/lib.d.ts 250 undefined Source file
FileWatcher:: Added:: WatchInfo: /Users/elads/Projects/testtsc/node_modules/typescript/lib/lib.es5.d.ts 250 undefined Source file
FileWatcher:: Added:: WatchInfo: /Users/elads/Projects/testtsc/node_modules/typescript/lib/lib.dom.d.ts 250 undefined Source file
FileWatcher:: Added:: WatchInfo: /Users/elads/Projects/testtsc/node_modules/typescript/lib/lib.webworker.importscripts.d.ts 250 undefined Source file
FileWatcher:: Added:: WatchInfo: /Users/elads/Projects/testtsc/node_modules/typescript/lib/lib.scripthost.d.ts 250 undefined Source file
DirectoryWatcher:: Added:: WatchInfo: /Users/elads/Projects/testtsc/node_modules/@types 1 undefined Type roots
Elapsed:: 0.2658340334892273ms DirectoryWatcher:: Added:: WatchInfo: /Users/elads/Projects/testtsc/node_modules/@types 1 undefined Type roots
[10:18:14 AM] Found 0 errors. Watching for file changes.

Files: 6
Lines of Library: 23413
Lines of Definitions: 0
Lines of TypeScript: 2
Lines of JavaScript: 0
Lines of JSON: 0
Lines of Other: 0
Identifiers: 39746
Symbols: 27134
Types: 9517
Instantiations: 2630
Memory used: 72906K
Assignability cache size: 3405
Identity cache size: 0
Subtype cache size: 0
Strict subtype cache size: 0
I/O Read time: 0.00s
Parse time: 0.12s
Program time: 0.13s
Bind time: 0.05s
Check time: 0.28s
printTime time: 0.01s
Emit time: 0.01s
transformTime time: 0.00s
commentTime time: 0.00s
I/O Write time: 0.00s
Total time: 0.47s
FileWatcher:: Triggered with main.ts 1:: WatchInfo: main.ts 250 undefined Source file
Scheduling update
Elapsed:: 0.469124972820282ms FileWatcher:: Triggered with main.ts 1:: WatchInfo: main.ts 250 undefined Source file
Synchronizing program
[10:18:24 AM] File change detected. Starting incremental compilation...

CreatingProgramWith::
roots: ["main.ts"]
options: {"watch":true,"extendedDiagnostics":true}
[10:18:24 AM] Found 0 errors. Watching for file changes.

Files: 6
Lines of Library: 23413
Lines of Definitions: 0
Lines of TypeScript: 2
Lines of JavaScript: 0
Lines of JSON: 0
Lines of Other: 0
Identifiers: 39746
Symbols: 27134
Types: 9517
Instantiations: 2630
Memory used: 91604K
Assignability cache size: 3405
Identity cache size: 0
Subtype cache size: 0
Strict subtype cache size: 0
I/O Read time: 0.00s
Parse time: 0.00s
Program time: 0.00s
Bind time: 0.00s
Check time: 0.26s
transformTime time: 0.01s
commentTime time: 0.00s
printTime time: 0.01s
Emit time: 0.01s
I/O Write time: 0.00s
Total time: 0.27s
FileWatcher:: Triggered with main.ts 1:: WatchInfo: main.ts 250 undefined Source file
Scheduling update
Elapsed:: 0.15825003385543823ms FileWatcher:: Triggered with main.ts 1:: WatchInfo: main.ts 250 undefined Source file
Synchronizing program
[10:18:25 AM] File change detected. Starting incremental compilation...

CreatingProgramWith::
roots: ["main.ts"]
options: {"watch":true,"extendedDiagnostics":true}
[10:18:25 AM] Found 0 errors. Watching for file changes.

Files: 6
Lines of Library: 23413
Lines of Definitions: 0
Lines of TypeScript: 2
Lines of JavaScript: 0
Lines of JSON: 0
Lines of Other: 0
Identifiers: 39746
Symbols: 23958
Types: 82
Instantiations: 0
Memory used: 78447K
Assignability cache size: 0
Identity cache size: 0
Subtype cache size: 0
Strict subtype cache size: 0
I/O Read time: 0.00s
Parse time: 0.00s
Program time: 0.00s
Bind time: 0.00s
Total time: 0.00s

thanks

[sshrshnv]

The same error in Typescript version 5.5.4 (macOS)