Preserve Existing or Split Multiline Flags

[jrc2139]

Summary

Preserve Existing Multiline Flags

If you write:

RUN --mount=type=cache,target=/a \
  --mount=type=cache,target=/b \
  go build

The formatter now preserves your line breaks instead of collapsing them.

Auto-Split Mount Flags (Default: ON)

Single-line mount flags are automatically split for readability:

Before:

RUN --mount=type=cache,target=/a --mount=type=cache,target=/b go build

After:

RUN --mount=type=cache,target=/a \
  --mount=type=cache,target=/b \
  go build

CLI Usage

Default behavior (split mount flags)

dockerfmt Dockerfile

Disable mount flag splitting

dockerfmt --split-mount-flags=false Dockerfile
dockerfmt -m=false Dockerfile

Files Modified

• lib/format.go - Added extractFlagsFormatted() and formatFlagsWithMountSplit() helpers
• cmd/root.go - Added --split-mount-flags / -m flag (default: true)
• dockerfmt_test.go - Enabled SplitMountFlags in test config
• tests/in/multiline-flags.dockerfile - New test cases
• tests/out/multiline-flags.dockerfile - Expected outputs
• tests/out/onbuild.dockerfile - Updated for new behavior