tally/syntax-directive-typo

Detects typos in # syntax= parser directives.

Property	Value
Severity	Error
Category	Correctness
Default	Enabled
Type	Fail-fast syntax check (exit code 4)

Description

The # syntax= directive at the top of a Dockerfile selects the BuildKit frontend image used to parse and build the file. A typo in this directive (e.g., docker/dokcerfile instead of docker/dockerfile) causes the build to fail immediately because the frontend image cannot be resolved. This check validates the directive value against well-known frontends (docker/dockerfile, docker.io/docker/dockerfile) and suggests corrections when the value is within a small edit distance. It also flags directives that contain whitespace, which is never valid. This is a fail-fast check: if a typo is detected, linting aborts with exit code 4.

Examples

Bad

# syntax=docker/dokcerfile:1.7
FROM alpine:3.20
RUN echo "hello"

Output:

Error: Dockerfile:1: syntax directive "docker/dokcerfile:1.7" looks misspelled (did you mean "docker/dockerfile:1.7"?)

Good

# syntax=docker/dockerfile:1.7
FROM alpine:3.20
RUN echo "hello"

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