Jinja Codegen

Jinja Codegen Mechanics

The jinja-templates rule states the invariant: all parameterized generated code goes through Minijinja templates, never raw format!/push_str/write! assembly. This skill covers the mechanics of doing that correctly.

Which template_env to call

There is no crate::template_env module. Each backend and generator owns its own template_env.rs:

• src/backends/<lang>/template_env.rs — per-language backend templates
• src/codegen/template_env.rs, src/core/template_env.rs, src/docs/template_env.rs, src/readme/template_env.rs, src/scaffold/template_env.rs, src/e2e/template_env.rs — shared/generator-specific templates

Call the one local to the code you are generating from:

out.push_str(&crate::backends::<lang>::template_env::render("block_name.jinja", minijinja::context! {
    key => value,
}));

Registering a template

Register in the backend's template_env.rs via include_str!:

("block_name.jinja", include_str!("templates/block_name.jinja")),

One template per logical unit (class header, method signature, enum variant, etc.) — do not create generic line/content passthrough templates to bypass the jinja-templates rule.

Engine settings

Set in each make_env(): trim_blocks = true, lstrip_blocks = true, keep_trailing_newline = true.

Inline templates

Allowed only for single-line fragments used inside a larger template or join operation. Inline renders must call .trim_end() or .trim_end_matches('\n') at the call site, because templates keep their trailing newline — omitting the trim doubles blank lines in the emitted output.

What Rust prepares vs. what the template owns

Rust prepares typed values, identifiers, escaped literals, symbol names, type names, file paths, enum/field metadata, booleans, comma-joined argument lists, and small expression fragments when they are not a logical emitted unit. Templates own generated-code structure, indentation, and multiline blocks.

Static push_str("literal\n") with no interpolation is fine to leave as-is — no template needed for non-parameterized strings.

Anti-patterns

• push_str(&format!(...)), write!/writeln! for interpolated output, or multiline format!(...)/format!(r#"..."#) that emits target code.
• format!(...) strings containing \n for generated code.
• Catch-all passthrough templates (e.g. formatted_line.jinja receiving content => format!(...)) used to route around the templating requirement.
• Calling crate::template_env::render — that module does not exist; use the local one.