`pretty-format-yaml` removes necessary quotes in flow sequences causing invalid YAML

[philipp-horstenkamp]

Description

The pretty-format-yaml hook removes quotes from scalar values inside flow-style sequences ([...]), even when those values contain special characters (like colons :) that must be quoted to produce valid YAML. This formatting breakage leads to syntax errors when parsing output (e.g., with Docker Compose or YAML linters).

---

Steps to Reproduce

1. Create a docker-compose.yaml with the following content:

   services:
     nc:
       image: nextcloud:31.0.7
       restart: unless-stopped
       healthcheck:
         test: [CMD, curl, -f, "http://localhost/status.php"]

2. Run pretty-format-yaml via pre-commit.
3. Formatter outputs:

   services:
     nc:
       image: nextcloud:31.0.7
       restart: unless-stopped
       healthcheck:
         test: [CMD, curl, -f, http://localhost/status.php]

4. YAML parser reports:

   while scanning a plain scalar
   found unexpected ':'
   

---

Expected Behavior

Quotes around scalars with special characters inside flow sequences must be preserved per YAML specification. The formatter should:

• Detect when quoting is necessary and preserve it automatically.
• Or offer a --preserve-quotes/--safe-syntax flag to avoid invalidating valid YAML.

---

Context

• YAML spec (1.1/1.2) mandates quotes for ambiguous scalars in flow sequences.
• Tools like Docker Compose rely on this, making the formatter’s behavior disruptive.

---

Proposal

Enhance pretty-format-yaml to:

• Automatically preserve necessary quotes in flow sequences.
• Or introduce a configuration option to enforce safe syntax preservation.

[ashrub-holvi]

• Or offer a --preserve-quotes

It's there