sneak cf13b275b7 Squashed commit of the following:

commit e15edaedd786254cf22c291a63a02f7cff33b119
Author: sneak <sneak@sneak.berlin>
Date:   Mon Jul 21 15:17:12 2025 +0200

    Implement YAML-first interpolation with type preservation

    Previously, interpolations were performed during string manipulation before
    YAML parsing, which caused issues with quoting and escaping. This commit
    fundamentally changes the approach:

    - Parse YAML first, then walk the structure to interpolate values
    - Preserve types: standalone interpolations can return numbers/booleans
    - Mixed content (text with embedded interpolations) always returns strings
    - Users control types through YAML syntax, not our quoting logic
    - Properly handle nested interpolations without quote accumulation

    This gives users explicit control over output types while eliminating
    the complex and error-prone manual quoting logic.

2025-07-21 15:19:28 +02:00

2.3 KiB

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Design: YAML-First Interpolation

Problem Statement

The current implementation performs string-based interpolation on the raw YAML file content before parsing. This approach has several issues:

Quoting complexity: We must handle YAML quoting rules manually, leading to edge cases and bugs
Type loss: All interpolated values become strings, even if they should be numbers or booleans
YAML special values: Values like "no", "yes", "true", "false", "on", "off" require special handling
Nested interpolation quoting: Complex logic needed to avoid double-quoting in nested interpolations
Fragile string manipulation: Operating on raw YAML text is error-prone

Proposed Solution

Parse the YAML file first, then walk the parsed structure to perform interpolations. This approach:

Leverages YAML parser: Let the YAML library handle all parsing, quoting, and escaping
Preserves types: Can return actual numbers, booleans, etc. from interpolations
Simplifies logic: No string manipulation or quoting logic needed
Clear semantics: Users control types through YAML syntax (quoted vs unquoted)
Robust: YAML serializer handles all edge cases correctly

Implementation Details

Constraints

Interpolation only occurs in YAML values, not keys
Users must properly quote interpolations if they want string output
The entire file must be valid YAML before interpolation

Workflow

Parse YAML file into a data structure (map/slice/scalar)
Recursively walk the structure:
- For string values: check for ${...} patterns and interpolate
- For other types: pass through unchanged
Handle the special env key to inject environment variables
Return the modified structure

Type Handling

Users control the output type through YAML syntax:

# String output (user quotes the interpolation)
port: "${ENV:PORT}"          # Result: "8080" (string)

# Numeric output (no quotes)
port: ${ENV:PORT}            # Result: 8080 (number)

# Boolean output
enabled: ${ENV:ENABLED}      # Result: true/false (boolean)

Benefits

Correctness: YAML parser handles all edge cases
Type safety: Preserves intended types
Simplicity: Removes complex string manipulation
Predictability: Users have explicit control over types
Maintainability: Less code, fewer edge cases

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