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transpile: Allow macro conversion to succeed only for some expansions #1806

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9174b20
transpile: Return `MacroExpansion` from `recreate_const_macro_from_ex…
Rua May 29, 2026
c2aaec2
transpile: Refactor `recreate_const_macro_from_expansions`
Rua May 14, 2026
5718463
transpile: Wrap `MacroExpansion` in `Rc` to avoid cloning
Rua May 15, 2026
d7d679d
transpile: Allow macro conversion to succeed only for some expansions
Rua May 15, 2026
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139 changes: 99 additions & 40 deletions c2rust-transpile/src/translator/macros.rs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,9 @@
use c2rust_ast_builder::mk;
use failure::format_err;
use indexmap::IndexMap;
use log::{info, trace};
use proc_macro2::{Span, TokenStream};
use std::rc::Rc;
use syn::{Expr, MacroDelimiter};

use crate::c_ast::{CDeclId, CExprId, CQualTypeId, CTypeId, CTypeKind};
Expand Down Expand Up @@ -30,14 +32,22 @@ impl<'c> Translation<'c> {
);

match maybe_replacement {
Ok((replacement, ty)) => {
Ok((replacement, expansion)) => {
trace!(" to {:?}", replacement);

let expansion = MacroExpansion { ty };
for (expr_id, result) in &expansion.expr_results {
if let Err(err) = result {
info!(
"Could not convert macro {} for {:?}: {}",
name, expr_id, err
);
}
}

let ty = self.convert_type(expansion.ty)?;
self.macro_expansions
.borrow_mut()
.insert(decl_id, Some(expansion));
let ty = self.convert_type(ty)?;
.insert(decl_id, Some(Rc::new(expansion)));

Ok(ConvertedDecl::Item(mk().span(span).pub_().const_item(
name,
Expand Down Expand Up @@ -68,43 +78,83 @@ impl<'c> Translation<'c> {
&self,
ctx: ExprContext,
expansions: &[CExprId],
) -> TranslationResult<(Box<Expr>, CTypeId)> {
let (val, ty) = expansions
) -> TranslationResult<(Box<Expr>, MacroExpansion)> {
struct ConvertedMacroExpr {
val: WithStmts<Box<Expr>>,
type_id: CTypeId,
}

let mut canonical: Option<ConvertedMacroExpr> = None;
let mut expr_results: IndexMap<_, _> = expansions
.iter()
.try_fold::<Option<(WithStmts<Box<Expr>>, CTypeId)>, _, _>(None, |canonical, &id| {
self.can_convert_const_macro_expansion(id)?;

let ty = self.ast_context[id]
.kind
.get_type()
.ok_or_else(|| format_err!("Invalid expression type"))?;
let expr = self.convert_expr(ctx, id, None)?;

// Join ty and cur_ty to the smaller of the two types. If the
// types are not cast-compatible, abort the fold.
let ty_kind = self.ast_context.resolve_type(ty).kind.clone();
if let Some((canon_val, canon_ty)) = canonical {
let canon_ty_kind = self.ast_context.resolve_type(canon_ty).kind.clone();
if let Some(smaller_ty) =
CTypeKind::smaller_compatible_type(canon_ty_kind.clone(), ty_kind)
{
if smaller_ty == canon_ty_kind {
Ok(Some((canon_val, canon_ty)))
} else {
Ok(Some((expr, ty)))
.map(|&expr_id| {
let result = self
.can_convert_const_macro_expansion(expr_id)
.and_then(|_| {
let type_id = self.ast_context[expr_id]
.kind
.get_type()
.ok_or_else(|| format_err!("Invalid expression type"))?;
let val = self.convert_expr(ctx, expr_id, None)?;
Ok(ConvertedMacroExpr { val, type_id })
})
.and_then(|new| {
// Join ty and cur_ty to the smaller of the two types. If the
// types are not cast-compatible, skip this expansion.
match &mut canonical {
Some(canonical) => {
let canon_type_kind = self
.ast_context
.resolve_type(canonical.type_id)
.kind
.clone();
let new_type_kind =
self.ast_context.resolve_type(new.type_id).kind.clone();
let smaller_type_kind = CTypeKind::smaller_compatible_type(
canon_type_kind.clone(),
new_type_kind,
);
let Some(smaller_type_kind) = smaller_type_kind else {
return Err(
format_err!(
"Not all macro expansions are compatible types"
)
.into()
)
};

if smaller_type_kind != canon_type_kind {
*canonical = new;
}
}

None => canonical = Some(new),
}
} else {
Err(format_err!("Not all macro expansions are compatible types"))
}
} else {
Ok(Some((expr, ty)))
}
})?
.ok_or_else(|| format_err!("Could not find a valid type for macro"))?;

Ok(())
});

(expr_id, result)
})
.collect();

let Some(canonical) = canonical else {
// If none of the expansions could be converted, try returning the first error we got.
let err = match expr_results.swap_remove_index(0) {
Some((_, Err(err))) => err,
_ => format_err!("Could not find a valid type for macro").into(),
};
return Err(err);
};

let ConvertedMacroExpr { val, type_id } = canonical;
let expansion = MacroExpansion {
ty: type_id,
expr_results,
};
val.wrap_unsafe()
.to_pure_expr()
.map(|val| (val, ty))
.map(|val| (val, expansion))
.ok_or_else(|| TranslationError::generic("Macro expansion is not a pure expression"))

// TODO: Validate that all replacements are equivalent and pick the most
Expand Down Expand Up @@ -169,23 +219,32 @@ impl<'c> Translation<'c> {
trace!(" found macro expansion: {macro_id:?}");
// Ensure that we've converted this macro and that it has a valid definition.
let expansion = self.macro_expansions.borrow().get(macro_id).cloned();
let macro_ty = match expansion {
let expansion = match expansion {
// Expansion exists.
Some(Some(expansion)) => expansion.ty,
Some(Some(expansion)) => expansion,

// Expansion wasn't possible.
Some(None) => return Ok(None),

// We haven't tried to expand it yet.
None => {
self.convert_decl(ctx, *macro_id)?;
if let Some(Some(expansion)) = self.macro_expansions.borrow().get(macro_id) {
expansion.ty
let expansion = self.macro_expansions.borrow().get(macro_id).cloned();

if let Some(Some(expansion)) = expansion {
expansion
} else {
return Ok(None);
}
}
};

if !matches!(expansion.expr_results.get(&expr_id), Some(Ok(_))) {
// Expansion succeeded in general, but not for this particular expression.
return Ok(None);
}

let macro_ty = expansion.ty;
let rust_name = self
.renamer
.borrow_mut()
Expand Down
4 changes: 2 additions & 2 deletions c2rust-transpile/src/translator/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -260,9 +260,9 @@ impl FuncContext {
}
}

#[derive(Clone)]
struct MacroExpansion {
ty: CTypeId,
expr_results: IndexMap<CExprId, TranslationResult<()>>,
}

type ZeroInits = IndexMap<CDeclId, (WithStmts<Box<Expr>>, IndexSet<Import>)>;
Expand All @@ -283,7 +283,7 @@ pub struct Translation<'c> {
zero_inits: RefCell<ZeroInits>,
function_context: RefCell<FuncContext>,
potential_flexible_array_members: RefCell<IndexSet<CDeclId>>,
macro_expansions: RefCell<IndexMap<CDeclId, Option<MacroExpansion>>>,
macro_expansions: RefCell<IndexMap<CDeclId, Option<Rc<MacroExpansion>>>>,
/// Sets of imports deferred while translating nested expressions for caching. Imports are
/// deferred when caching translations to make them pure and thus cache the translation
/// alongside its required imports. Each additional nested level of caching translation
Expand Down
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