Wrong detection of up-to-date state composite project with no included files

[timocov]

TypeScript Version: 3.5.0-dev.20190507, 3.4.4

Search Terms: composite projects

Let's say we have a composite project with the following structure:

├── src
│   ├── folder
│   │   ├── index.ts
│   │   ├── tsconfig.json
│   ├── folder2
│   │   ├── index.ts
│   │   ├── tsconfig.json
│   └── tsconfig.json
├── tests
│   ├── index.ts
│   ├── tsconfig.json
└── tsconfig.json

where src/tsconfig.json refers to src/folder and src/folder2 composite sub-projects, tests/tsconfig.json refers to src/ and includes tests/index.ts module. Both src/folder and src/folder2 projects includes they local index.ts modules.

tsconfig.json from the root refers to src/ and tests/ sub-projects.

So, such project we build via ./node_modules/.bin/tsc -b . --verbose.

For the first run we have the following output:

[15:55:32] Projects in this build:
    * src/folder/tsconfig.json
    * src/folder2/tsconfig.json
    * src/tsconfig.json
    * tests/tsconfig.json
    * tsconfig.json

[15:55:32] Project 'src/folder/tsconfig.json' is out of date because output file 'src/folder/index.js' does not exist

[15:55:32] Building project 'src/folder/tsconfig.json'...

[15:55:35] Project 'src/folder2/tsconfig.json' is out of date because output file 'src/folder2/index.js' does not exist

[15:55:35] Building project 'src/folder2/tsconfig.json'...

[15:55:36] Project 'tests/tsconfig.json' is out of date because its dependency 'src' is out of date

[15:55:36] Building project 'tests/tsconfig.json'...

It looks fine for now. But if we compile it in the next time without any change of the code we'll get the following:

[15:57:11] Projects in this build:
    * src/folder/tsconfig.json
    * src/folder2/tsconfig.json
    * src/tsconfig.json
    * tests/tsconfig.json
    * tsconfig.json

[15:57:11] Project 'src/folder/tsconfig.json' is up to date because newest input 'src/folder/index.ts' is older than oldest output 'src/folder/index.js'

[15:57:11] Project 'src/folder2/tsconfig.json' is up to date because newest input 'src/folder2/index.ts' is older than oldest output 'src/folder2/index.js'

[15:57:11] Project 'tests/tsconfig.json' is out of date because its dependency 'src' is out of date

[15:57:11] Building project 'tests/tsconfig.json'...

[15:57:12] Updating unchanged output timestamps of project 'tests/tsconfig.json'...

As you can see, the compiler treats tests/tsconfig.json project as out of date because of out of date src project. But we don't change anything.

It looks like the problem happens only if a project refers to another project(s) without including any file (src/tsconfig.json refers to src/folder and src/folder2 and include nothing).

If we add any file to src/tsconfig.json project no recompilation of tests happened.

Note: according #3469 (comment)

Another good practice is to have a "solution" tsconfig.json file that simply has references to all of your leaf-node projects.

Code

Here is zip with a project I describe above, just unzip it, run npm install and then run twice npm run build.

bug.zip

Expected behavior:

No recompilation in the second time if we change nothing.

Actual behavior:

Recompilation on each build even if we change nothing.

Related Issues: #3469