LogQL Pipeline Formatting (label_format, line_format, decolorize)

[frisbeeman]

Overview

Implement LogQL pipeline formatting stages that transform labels and log lines using Go template syntax.

Parent Issue

Part of #6 (Query Service Implementation), delegated from #8 (LogQL Query Compiler).

Context

Pipeline formatting stages allow users to transform labels and log lines. Currently, all formatting stages are no-op placeholders that return the DataFrame unchanged.

Requirements

Formatting Stages to Implement

Stage	Syntax	Description
label_format	| label_format new="{{.old}}"	Create/modify labels using Go templates
line_format	| line_format "{{.level}}: {{.message}}"	Reformat the entire log line
decolorize	| decolorize	Remove ANSI color codes from log lines

Example Queries

{job="app"} | label_format level_upper="{{.level | ToUpper}}"
{job="app"} | line_format "{{.timestamp}} [{{.level}}] {{.message}}"
{job="app"} | decolorize

Implementation Approach

1. Add gtmpl crate for Go template parsing and rendering

2. Create UDFs in src/query/logql/datafusion/udf.rs:

   • label_format_template(template: String, ...labels) -> String
   • line_format_template(template: String, ...labels) -> String
   • decolorize(text: String) -> String (ANSI regex removal)

3. Update planner in src/query/logql/datafusion/planner.rs:

   • Replace no-op implementations in apply_label_format(), apply_line_format(), apply_decolorize()

Acceptance Criteria

• label_format creates/modifies labels using Go template syntax
• line_format transforms log lines using Go template syntax
• decolorize removes ANSI escape sequences
• Go template functions (ToUpper, ToLower, Replace, etc.) are supported
• Template errors are handled gracefully
• Unit tests for each formatting stage
• Integration tests with full LogQL queries

Dependencies

• gtmpl crate for Go template parsing

Technical References

• LogQL Label Format
• LogQL Line Format
• Current placeholder: src/query/logql/datafusion/planner.rs
• Technical spec: src/query/logql/TECHNICAL_SPEC.md Section 7.1.9-7.1.10