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Document some parts of ConstantEvaluator. #2489

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Sep 19, 2023
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Document some parts of ConstantEvaluator. #2489

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11 changes: 11 additions & 0 deletions src/proc/constant_evaluator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -124,9 +124,13 @@ impl ConstantEvaluator<'_> {
| Expression::Compose { .. }
| Expression::Splat { .. } => Ok(expr),
Expression::Constant(c) => {
// Are we working in a function's expression arena, or the
// module's constant expression arena?
if let Some(const_expressions) = self.const_expressions {
// Deep-copy the constant's value into our arena.
self.copy_from(self.constants[c].init, const_expressions)
} else {
// "See through" the constant and use its initializer.
Ok(self.constants[c].init)
}
}
Expand Down Expand Up @@ -786,6 +790,13 @@ impl ConstantEvaluator<'_> {
Ok(self.register_constant(expr, span))
}

/// Deep copy `expr` from `expressions` into `self.expressions`.
///
/// Return the root of the new copy.
///
/// This is used when we're evaluating expressions in a function's
/// expression arena that refer to a constant: we need to copy the
/// constant's value into the function's arena so we can operate on it.
fn copy_from(
&mut self,
handle: Handle<Expression>,
Expand Down