--watch and --build flags work inconsistently in monorepo

[stereobooster]

TypeScript Version: 3.5.2

Search Terms:

watch monorepo

Code

https://github.com/stereobooster/typescript-monorepo/tree/typescript-bug

(or https://github.com/stereobooster/learn-a/tree/watch-bug)

Expected behavior:

When I run yarn tsc --build I get an error

packages/b/src/B.tsx:5:1 - error TS2362: The left-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type.

5 "" / 0;
  ~~

but when I run watch it reports 0 errors:

[11:02:07 AM] Found 0 errors. Watching for file changes.

Actual behavior:

I expect watch mode to report errors.

Playground Link: need to clone repo, because it is monorepo

Related Issues: There are similar issues, but are not same

RyanCavanaugh/learn-a#16

[sheetalkamat]

This is working as intended. In your steps you mention running tsc --w that's just going to run on the root tsconfig (and not on whole dependency graph) and its similar to doing tsc but with watch.
What you want to do is tsc --build --watch instead and you will see the errors.

[10:24:52 AM] Starting compilation in watch mode...

[10:24:52 AM] Projects in this build:
    * packages/d/tsconfig.json
    * packages/b/tsconfig.json
    * packages/c/tsconfig.json
    * tsconfig.json

[10:24:52 AM] Project 'packages/d/tsconfig.json' is up to date because newest input 'packages/d/src/d.ts' is older than oldest output 'packages/d/lib/d.js.map'

[10:24:52 AM] Project 'packages/b/tsconfig.json' is out of date because output file 'packages/b/lib/B.js' does not exist

[10:24:52 AM] Building project 'c:/temp/typescript-monorepo/packages/b/tsconfig.json'...

packages/b/src/B.tsx:5:1 - error TS2362: The left-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type.

5 "" / 0;
  ~~

[10:24:56 AM] Project 'packages/c/tsconfig.json' is up to date because newest input 'packages/c/src/index.ts' is older than oldest output 'packages/c/lib/index.js'

[10:24:56 AM] Found 1 error. Watching for file changes.

[stereobooster]

You can combine --watch and --build didn't know that. TIL. Thanks