Error if command-line options are specified when a `tsconfig.json` is present

[DanielRosenwasser]

From #54500:

Currently if you run tsc foo.ts in a folder where a tsconfig.json exists, the tsconfig file is completely ignored. This is very confusing. The intended meaning of this is also unclear; it could be that you want to use the compilerOptions of the config but not the files and/or include and/or exclude.

For clarity, in 6.0, if you run tsc in a directory with a tsconfig.json, an error will be issued instead.

tsconfig.json is present but will not be loaded if files are specified on the commandline. Use --ignore-config to skip this error

Basically, it should be okay to run

• tsc -p tsconfig.json [other options] - the user has explicitly opted into using the tsconfig.json, but wants to override some options (even files)
• tsc with no options - regardless of what is run (probably continue just show a basic help screen)

But if you run without -p/--project, you should receive an error if there is a tsconfig.json present and it may be a mistake to build without your project; and that if it was intentional to ignore it, specify --ignoreConfig.

About --ignoreConfig

• It should be okay to have this option even if there is no tsconfig in the CWD
• I don't know if it should be called --ignoreProject instead of --ignoreConfig
• I don't know if we can error if this option is specified within the tsconfig.json, but that probably would be ideal.

[mrazauskas]

if it was intentional to ignore it, specify --ignoreConfig.

Perhaps simply tsc --project ignore or tsc --project force-ignore? (Might overlap with a real project name, but does not require adding new option and will not be possible to specify within the tsconfig.json.)

[DanielRosenwasser]

Yeah, it's an interesting option, but I'd rather not specify something that can clash with a real directory name. Plus the discrete flag isn't much to maintain and feels more clear.

[uhyo]

I really really really really really need this, can't wait for TS 6.0 😭

AI agents (for me it is Claude Code) literally always try to run tsc foo.ts bar.ts to save time (apparently).

Then they get huge amount of errors and go like:

1. 🤖 Oh, the errors are due to configuration problems, not related to my changes..., or
2. 🤖 Oh this project targets ES5, so I can't use ES2015 methods, let's fix the issue...

So a helpful error message that guides users (AIs) to run tsc without command-line parameters would be great.