feat: support strings.render_template

[fatelei]

cargo test -r --test opa -- v1/rendertemplate
Compiling regorus v0.2.5 (/Users/fatelei/github/regorus)
Finished release profile [optimized + debuginfo] target(s) in 1.75s
Running tests/opa.rs (target/release/deps/opa-f3ff12037003e175)
OPA TESTSUITE: target/opa/branch/v0.68.0/test/cases/testdata
0: rendertemplate/simple PASSED
1: rendertemplate/simpleint PASSED
2: rendertemplate/complex PASSED
3: rendertemplate/missingkey PASSED

OPA TESTSUITE STATUS
FOLDER PASS FAIL
v1/rendertemplate : 4 0

TOTAL

cargo test -r --test opa -- rendertemplate
Finished release profile [optimized + debuginfo] target(s) in 0.20s
Running tests/opa.rs (target/release/deps/opa-f3ff12037003e175)
OPA TESTSUITE: target/opa/branch/v0.68.0/test/cases/testdata

OPA TESTSUITE STATUS
FOLDER PASS FAIL

Error: no matching tests found.
error: test failed, to rerun pass --test opa

Caused by:
process didn't exit successfully: /Users/fatelei/github/regorus/target/release/deps/opa-f3ff12037003e175 rendertemplate (exit status: 1)

[fatelei]

@microsoft-github-policy-service agree

[Copilot]

Pull request overview

This PR adds support for the strings.render_template builtin function to the Regorus OPA interpreter, enabling Go-style template rendering with variable interpolation, conditional blocks (if), and iteration constructs (range). The implementation also includes two minor fixes: correcting pattern matching in the interpreter's default rule handling and making lifetime annotations explicit in the time compatibility module.

• Added strings.render_template builtin function with support for Go template syntax including variable interpolation, conditional rendering, and iteration over arrays/sets/objects
• Fixed pattern matching in interpreter.rs to properly use .as_ref() for comparing optional default rule indices
• Made lifetime annotations explicit in builtins/time/compat.rs for better code clarity

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
src/builtins/strings.rs	Adds the complete strings.render_template implementation with helper functions for expression evaluation, block parsing, and template rendering
src/interpreter.rs	Fixes pattern matching for default rule index comparison to use .as_ref()
src/builtins/time/compat.rs	Changes implicit lifetime '_ to explicit 'a in impl block

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[anakrish]

@fatelei Thanks for the contribution. CoPilot has provided very good feedback above.

[fatelei]

@fatelei Thanks for the contribution. CoPilot has provided very good feedback above.

ok

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 7 comments.

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[anakrish]

Hey @fatelei,
Thanks for the contribution. Given that templating is a language in itself, it would be good to add test cases here: https://github.com/microsoft/regorus/tree/main/tests/interpreter/cases/builtins/strings

covering all the interesting cases.

[anakrish]

@fatelei, It is not exactly clear to me what the template language semantics are. Is this the spec: https://pkg.go.dev/text/template

[fatelei]

@fatelei, It is not exactly clear to me what the template language semantics are. Is this the spec: https://pkg.go.dev/text/template

yes

[fatelei]

Thanks for the contribution. Given that templating is a language in itself, it would be good to add test cases here: https://github.com/microsoft/regorus/tree/main/tests/interpreter/cases/builtins/strings

covering all the interesting cases.

add

[anakrish]

Hey @fatelei,

Can you comment out the following lines:

regorus/src/builtins/mod.rs

Lines 4 to 15 in 5afbd96

	#![allow(
	clippy::arithmetic_side_effects,
	clippy::expect_used,
	clippy::indexing_slicing,
	clippy::panic,
	clippy::shadow_unrelated,
	clippy::unwrap_used,
	clippy::missing_const_for_fn,
	clippy::option_if_let_else,
	clippy::semicolon_if_nothing_returned,
	clippy::useless_let_if_seq
	)] // builtins perform validated indexing and intentional arithmetic/string ops

and then adjust code to work correctly?

We are in the process of hardening regorus. Hence you see many recent PRs that fix similar issues in different files/components.

Also, it is important to set some maximum recursion depth, avoid infinite loops etc. The goal is that one badly written policy should not hog cpu/cause a crash.

Since your PR involves implementing support for an entire sub language (templating), I haven't been able to spend as much time as I would like to review it. Sorry for the delay. I will prioritize this soon.