Rules template

Bazel rules and a Go command for rendering template files

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3: Bzl

rules_template provides Bazel rules and a Go command for rendering template files. A registered toolchain supplies the templating executable to build actions.

Getting started

MODULE.bazel:

bazel_dep(name = "rules_template", version = "<VERSION>")
register_toolchains("@rules_template//main/bzl:all")

BUILD.bazel:

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project-dns Specification

Purpose

Record the retirement of rules_template landing infrastructure while preserving its reusable Bazel module.

Requirements

Requirement: Keep landing infrastructure retired

The module SHALL follow the tools boundary and SHALL have no dedicated landing DNS declarations, Terraform root, or operational source exports.

Scenario: Inspect the module after landing retirement

WHEN the module is consumed from tools/rules_template
THEN its reusable Bazel rules remain available without landing infrastructure.

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Rules template

Purpose

Render Go text templates from declared data files through a command and a Bazel toolchain rule. This source baseline was observed on 2026-09-08 at revision 550d7e79b1f5fdbc2b6017b75178471d6914082f. The command operates on one template and output per invocation; the rule’s list attributes do not establish a multi-template rendering guarantee.

Sources: project description, command flags, templater, template functions, and Bazel action.

Requirements

Requirement: Load supported data formats into template context

The template command SHALL load data files in argument order into DataFiles, decode .toml, .json, .ndjson, and .yaml data, and expose .txt files as lines without structured decoding. --extension SHALL override extension selection for the supplied data files.

Scenario: A caller renders a template using newline-delimited JSON

WHEN a declared .ndjson input contains valid JSON on each data line
THEN its template context contains a parsed sequence in Data and the input lines in Lines.

Requirement: Report unsupported formats and rendering failures

The command SHALL return errors for unsupported data extensions, failed reads, invalid structured data, invalid template syntax, template execution failures, and failed output writes.

Scenario: A data file uses an unsupported extension

WHEN a data path has an unrecognized extension and no supported override
THEN rendering fails with an unsupported-extension diagnostic identifying the data path.

Requirement: Expose the registered template function set

Template execution SHALL use the project’s function map, including JSON serialization, HTML escaping, path basename and dirname helpers, and first and last element helpers.

Scenario: A template serializes structured data

WHEN a valid template invokes to_json on JSON-serializable context data
THEN the function returns the JSON representation for inclusion in the output.

Requirement: Render declared Bazel inputs with the selected toolchain

template_run_binary SHALL invoke the registered templater with its template subcommand, declare source and data files as inputs, declare output files, and forward additional rule arguments.

Scenario: A target declares one template and one output

WHEN Bazel executes the target with its registered template toolchain
THEN the action passes the template, ordered data flags, and output path to the templater and exposes the declared output to downstream targets.

3 - Bzl

Bazel code