ecko explain, lint and fix

Three tools that read a program and tell you something about it. lint is mechanical; the other two use a model.

ecko lint

ecko lint file.ecko

Reports code that is present but doing nothing:

• dead code after a return, break or continue
• unused imports
• unused variables
• unreachable branches

No model involved, no network. This overlaps ecko check - the split is that check answers "is this wrong?" and gates the run, while lint answers "is this needed?" and never does.

ecko explain

ecko explain file.ecko

Static analysis plus a model, producing prose: what the program does, how it is structured, what stands out. Useful on code you did not write, or wrote long enough ago that it counts.

It reads the program. It does not run it, so it cannot tell you what the program actually did with real input.

ecko fix

ecko fix file.ecko

Takes the errors in a file and suggests a repair. It prints the suggestion; it does not edit your file.

fix also carries mechanical migrations, which do rewrite files and are worth knowing about because they are exact rather than suggested.

ecko fix --migrate

Rewrites deprecated syntax to the form that replaced it.

ecko fix --migrate --list          # what can be migrated, and what runs by default
ecko fix --migrate --check src/    # report, write nothing (exit 2 if any file needs it)
ecko fix --migrate src/            # rewrite in place
ecko fix --migrate --only=const src/

Today that means const to let, and |x| ... lambdas to fn(x) .... Both still parse and run; ecko check warns about them, and a future major version removes them.

ecko fmt canonicalises the same forms while it formats. Reach for --migrate when the project is not formatted with fmt: it touches only the deprecated constructs, so the diff is the migration rather than a whole-file reflow.

One-time codemods

ecko fix --migrate --only=bytes src/     # *_decode -> *_decode_text
ecko fix --migrate --only=exports src/   # the old `export { ... }` block to inline `export`

(The older --migrate-bytes and --migrate-exports spellings still work.)

These belong to specific past breaking releases, and they are not run by plain --migrate. A deprecation rewrite is a canonicalisation, so running it on already-canonical code changes nothing. A codemod is a reinterpretation: it cannot tell code that has already been migrated from code that never needed it. Run the bytes codemod twice and it rewrites a correct base64_decode - which wants bytes - into base64_decode_text, which does not.

Which to reach for

check, lint and fmt need no key. explain and fix produce mock output without one.