TS 5.6 `files` missing from `--showConfig` (with absolute / ``${configDir}`` `include` paths)

🔎 Search Terms

"--showConfig", "include", "configDir", "files", "extends", "absolute"

🕗 Version & Regression Information

• Tested versions:
  • 3.2.1 (--showConfig was introduced here)
  • 3.2.4
  • 5.5.2 (${configDir} was introduced here)
  • latest => 5.6.3
  • next =>5.7.0-dev.20241011
• This is the behaviour in every version I tried, and I reviewed the FAQ for entries about "configDir", "showConfig", "absolute".
• I was unable to test this on prior versions because --showConfig cli flag was introduced in TS 3.2 and configDir template variable was introduced in TS 5.5.

⏯ Playground Link

No response

💻 Code

// tsconfig-rel.json
{
    //...
    "include": ["src/**/*"]
}

// tsconfig-abs.json
{
    //...
    "include": ["/path/to/src/**/*"]
}

// tsconfig-cnf.json
{
    //...
    "include": ["${configDir}/src/**/*"]
}

// src/index.ts
console.log("dummy");

🙁 Actual behavior

❌ Printing config yields different results.

npx tsc --project tsconfig-rel.json --showConfig
npx tsc --project tsconfig-abs.json --showConfig
npx tsc --project tsconfig-cnf.json --showConfig

• For absolute include paths the files property is missing.
• ${configDir} is resolved to and behaves / fails the same as absolute paths.

  {
      "compilerOptions": {...},
-     "files": [
-         "./src/index.ts"
-     ],
      "include": [
-         "src/**/*"
+         "/path/to/src/**/*"
      ],
      "exclude": [...]
  }

✅ Listing files yields the same output.

npx tsc --project tsconfig-rel.json --listFiles --noEmit
npx tsc --project tsconfig-abs.json --listFiles --noEmit
npx tsc --project tsconfig-cnf.json --listFiles --noEmit

List of files printed to stdout, containing

• /path/to/src/index.ts
• /path/to/node_modules/**/*.d.ts entries from npm dependency type declarations.
• /path/to/node_modules/typescript/lib/lib.decorators.d.ts (only in TS 5 of course)
• /path/to/node_modules/typescript/lib/lib.decorators.legacy.d.ts (only in TS 5 of course)

✅ Building yields the same index.js file content for all configs.

npx tsc --project tsconfig-rel.json
npx tsc --project tsconfig-abs.json
npx tsc --project tsconfig-cnf.json

🙂 Expected behavior

--showConfig should show the same files for configs that build the same files and show the same listing for --listFiles.

Additional information about the issue

includeRe in matchesSpecs seems to be calculated differently for absolute / relative paths, resulting in all files being filtered out in convertToTSConfig.

I can't tell though which behaviour is actually expected. (keep files or filter files out?)

Start in src/compiler/commandLineParser.ts at matchesSpecs and convertToTSConfig, where the issue reports different handling of absolute and relative include paths. Reproduce the three tsconfig cases with tsc --showConfig, then determine the expected files output and verify that it matches the files selected by --listFiles and the build.