Function parameter is overridden by a same-named global variable

[logbie]

Summary

When a function (action) parameter has the same name as an existing global variable, calls to that action ignore the passed argument and use the global's value instead. Parameters should shadow globals, not be overwritten by them.

Minimal reproduction

define action called takes_p with parameters p:
    return p
end action

store p as "GLOBAL-VALUE"
display "expected 'arg', got: " with takes_p of "arg"

Actual output:

expected 'arg', got: GLOBAL-VALUE

Expected output:

expected 'arg', got: arg

By contrast, an action-local variable (store loc as ...) correctly shadows a same-named global — only parameters are affected.

Impact

This is a silent correctness bug. Any library that defines actions with common parameter names (t, s, v, i, name, value, node, …) will misbehave the moment a caller happens to have a global of the same name — with no error, just wrong results.

I hit this building a templating engine in WFL: internal helpers with parameters named t/v were silently overwritten whenever the calling program had globals of those names, corrupting every result. The workaround was to prefix every parameter with a rare marker (sc_), which shouldn't be necessary.

Environment

• wfl built from source at current main
• rustc 1.94.1, cargo 1.94.1, Linux

Suggested fix

Parameter bindings should be introduced into the action's own local scope and take precedence over globals during name resolution inside the action body.

[logbie]

Assessment: confirmed bug — silent correctness issue in parameter binding.

Reproduced the root cause against main. Action parameters are bound with Environment::define() (src/interpreter/mod.rs:8481, and :4890/:4892 for event/handler params). But define() (src/interpreter/environment.rs:70) rejects a name that already exists in a parent scope:

if let Some(parent_weak) = &self.parent
    && let Some(parent) = parent_weak.upgrade()
    && parent.borrow().has(name)
{
    return Err(format!("Variable '{name}' has already been defined in an outer scope. ..."));
}

The call site discards that error (let _ = call_env.borrow_mut().define(param, arg.clone());), so when a same-named global exists the parameter is never bound in the call scope — and the body's lookup falls through to the global. That's exactly your takes_p of "arg" → GLOBAL-VALUE. An action-local store shadows correctly because it goes through declare_variable, not this parent-checking define.

Fix shape: bind parameters with define_direct() (environment.rs:116) instead of define(). define_direct only checks the current scope, so a parameter unconditionally shadows any parent/global of the same name — which is the correct scoping rule and what you'd expect. It exists precisely for "existence in parent scopes already handled" cases. Backward-compatible: it only adds the missing local binding; nothing that currently works relies on a parameter silently resolving to a global. TDD: your minimal repro asserting takes_p of "arg" == "arg" with a global p present. Suggested labels: bug, interpreter.

Posted by the WFL repo warden (automated triage pass).

[logbie]

Fixed on branch claude/github-issues-review-i7upri.

Parameters were bound with Environment::define(), which rejects a name already present in a parent scope; the call site discarded that error, so with a same-named global the parameter was never bound and the body fell through to the global. Parameters are now bound with define_direct() (current scope only) in both the action-call path (call_function) and the event-handler path, so a parameter unconditionally shadows any same-named global/outer binding — exactly the fix shape in the triage note. takes_p of "arg" with a global p now returns arg. Regression tests (single- and multi-param) added.

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Generated by Claude Code

[logbie]

Confirmed fixed on main (2c52826, #587). The minimal repro now prints arg, and I re-ran the full Scribe templating engine test suite against the patched build — 32/32 pass even with a hostile global environment (t, v, s, i, name, val, node all defined as globals) that previously corrupted every render. Thanks for the quick turnaround. Safe to close from my side.

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Generated by Claude Code

[logbie]

Verified fixed on WFL 26.7.36 (fc21f2f, Linux release build) during the #610 Phase 1 open-issue inventory.

Fixed by PR #587 — action/event parameter binding was switched from define() (which rejected outer-scope names) to define_direct() (current-scope only), so parameters now unconditionally shadow same-named globals instead of being silently overwritten.

Repro now produces the correct result:

$ wfl repro.wfl
got: arg
[exit 0]

The silent-correctness bug (parameter overwritten by a same-named global) is resolved. Closing as completed.

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Generated by Claude Code