[LegacyKeyValueFormat] Document multi-line leading space change

[homersimpsons]

Is this a docs issue?

• My issue is about the documentation content or website

Type of issue

Other

Description

In https://docs.docker.com/reference/build-checks/legacy-key-value-format/ we see the following example:

But they are not strictly equal (as observed in rust-lang/rust#153109 (comment)):

1. The "Bad" example gives DEPS="curl git make"
2. The "Good" example gives DEPS=" curl git make" (leading whitespaces)

FROM alpine:3.20

ENV DEPS \
 curl \
 git \
 make

CMD ["printenv", "DEPS"]

$ docker build -t tmp . && docker run --rm tmp
[...]
curl git make

Location

https://docs.docker.com/reference/build-checks/legacy-key-value-format/

Suggestion

I believe this behaviour change should be documented.

Or maybe this is a Docker bug where the \ should always strip the leading whitespace of the following line? Which would gives curl git make in both cases?

This example was introduced in moby/buildkit#5126.

[homersimpsons]

Similarly, changes about escapes could be highlighted:

-ENV SCRIPT_SOURCE python3 ../x.py --stage 2 test --host='' --target riscv64gc-unknown-linux-gnu
+ENV SCRIPT_TARGET="python3 ../x.py --stage 2 test --host= --target riscv64gc-unknown-linux-gnu"

-ENV ARGS_SOURCE --set 'rust.codegen-backends=[\"llvm\",\"gcc\"]'
+ENV ARGS_TARGET="--set rust.codegen-backends=[\\\"llvm\\\",\\\"gcc\\\"]"