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transpile: Properly handle address-of static compound literals #1644

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7e0a07c
transpile: Rearrange `DeclRef` code in `convert_expr` a bit
Rua Mar 23, 2026
0c63b79
transpile: Mark `DeclRef`s for static variables as `unsafe`
Rua Mar 23, 2026
1e338ea
transpile: Split off `convert_compound_literal` function
Rua Mar 6, 2026
b3e8e44
transpile: Allow `WithStmts` to have Item statements in statics
Rua Mar 6, 2026
dccadf5
transpile: Properly handle address-of static compound literals
Rua Mar 23, 2026
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58 changes: 58 additions & 0 deletions c2rust-transpile/src/translator/literals.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -139,6 +139,64 @@ impl<'c> Translation<'c> {
bytes_padded
}

/// Convert a C compound literal expression to a Rust expression.
pub fn convert_compound_literal(
&self,
ctx: ExprContext,
qty: CQualTypeId,
val: CExprId,
override_ty: Option<CQualTypeId>,
) -> TranslationResult<WithStmts<Box<Expr>>> {
// C compound literals are lvalues, but equivalent Rust expressions generally are not.
// So if an address is needed, store it in an intermediate variable first.
if !ctx.needs_address() || ctx.expanding_macro.is_some() {
return self.convert_expr(ctx, val, override_ty);
}

let fresh_name = self.renamer.borrow_mut().fresh();
let fresh_ty = self.convert_type(override_ty.unwrap_or(qty).ctype)?;

// Translate the expression to be assigned to the fresh variable.
// It will be assigned by value, so we don't need its address anymore.
let val = self.convert_expr(ctx.set_needs_address(false), val, override_ty)?;

val.and_then(|val| {
// If we are translating a static variable,
// then the fresh variable should also be static.
if ctx.is_static {
let item = mk().mutbl().static_item(&fresh_name, fresh_ty, val);
let fresh_stmt = mk().item_stmt(item);
let mut val = WithStmts::new(vec![fresh_stmt], mk().ident_expr(fresh_name));

// Accessing a static variable is unsafe.
// In the current nightly, this applies also to taking a raw pointer,
// but this requirement was removed in later versions of the
// `raw_ref_op` feature.
if self.tcfg.edition < Edition2024 {
val.set_unsafe();
}

Ok(val)
} else {
let mutbl = if qty.qualifiers.is_const {
Mutability::Immutable
} else {
Mutability::Mutable
};
let local = mk().local(
mk().set_mutbl(mutbl).ident_pat(&fresh_name),
Some(fresh_ty),
Some(val),
);
let fresh_stmt = mk().local_stmt(Box::new(local));
Ok(WithStmts::new(
vec![fresh_stmt],
mk().ident_expr(fresh_name),
))
}
})
}

/// Convert an initialization list into an expression. These initialization lists can be
/// used as array literals, struct literals, and union literals in code.
pub fn convert_init_list(
Expand Down
227 changes: 105 additions & 122 deletions c2rust-transpile/src/translator/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1685,7 +1685,6 @@ impl<'c> Translation<'c> {

use CExprKind::*;
match self.ast_context[expr_id].kind {
DeclRef(_, _, LRValue::LValue) => return true,
ImplicitCast(_, _, cast_kind, _, _) | ExplicitCast(_, _, cast_kind, _, _) => {
use CastKind::*;
match cast_kind {
Expand Down Expand Up @@ -2143,21 +2142,47 @@ impl<'c> Translation<'c> {
ref attrs,
..
} if has_static_duration || has_thread_duration => {
if has_thread_duration {
self.use_feature("thread_local");
}

let new_name = &self
.renamer
.borrow()
.get(&decl_id)
.expect("Variables should already be renamed");

let mut static_def = if is_externally_visible {
mk_linkage(false, new_name, ident, self.tcfg.edition)
.pub_()
.extern_("C")
} else if self.cur_file.get().is_some() {
mk().pub_()
} else {
mk()
};

// Force mutability due to the potential for raw pointers occurring in the type
// and because we may be assigning to these variables in the external initializer
static_def = static_def.mutbl();

if has_thread_duration {
self.use_feature("thread_local");
static_def = static_def.single_attr("thread_local");
}

// Add static attributes
for attr in attrs {
static_def = match attr {
c_ast::Attribute::Used => static_def.single_attr("used"),
c_ast::Attribute::Section(name) => {
static_def.str_attr("link_section", name)
}
_ => continue,
};
}

let ctx = ctx.static_();

// Collect problematic static initializers and offload them to sections for the linker
// to initialize for us
let (ty, init) = if self.static_initializer_is_uncompilable(initializer, typ) {
if self.static_initializer_is_uncompilable(initializer, typ) {
// Note: We don't pass `is_const` through here. Extracted initializers are run
// outside of the static initializer, in a non-const context.
let ctx = ctx.not_const();
Expand Down Expand Up @@ -2186,55 +2211,28 @@ impl<'c> Translation<'c> {

self.add_static_initializer_to_section(ctx, new_name, typ, &mut init)?;

(ty, init)
Ok(ConvertedDecl::Item(
static_def.span(span).static_item(new_name, ty, init),
))
} else {
let ConvertedVariable { ty, mutbl: _, init } =
self.convert_variable(ctx.const_(), initializer, typ)?;
let mut init = init?;
let mut items = init.stmts_to_items().ok_or_else(|| {
format_err!("Expected only item statements in static initializer")
})?;

// TODO: Replace this by relying entirely on
// WithStmts.is_unsafe() of the translated variable
if self.static_initializer_is_unsafe(initializer, typ) {
init.set_unsafe()
}
let init = init.to_unsafe_pure_expr().ok_or_else(|| {
format_err!("Expected no side-effects in static initializer")
})?;

(ty, init)
};
let init = init.to_unsafe_pure_expr().unwrap();
let item = static_def.span(span).static_item(new_name, ty, init);
items.push(item);

let static_def = if is_externally_visible {
mk_linkage(false, new_name, ident, self.tcfg.edition)
.pub_()
.extern_("C")
} else if self.cur_file.get().is_some() {
mk().pub_()
} else {
mk()
};

// Force mutability due to the potential for raw pointers occurring in the type
// and because we may be assigning to these variables in the external initializer
let mut static_def = static_def.span(span).mutbl();
if has_thread_duration {
static_def = static_def.single_attr("thread_local");
}

// Add static attributes
for attr in attrs {
static_def = match attr {
c_ast::Attribute::Used => static_def.single_attr("used"),
c_ast::Attribute::Section(name) => static_def
.unsafety(attr_unsafety(self.tcfg.edition))
.str_attr("link_section", name)
.unsafety(Unsafety::Normal),
_ => continue,
}
Ok(ConvertedDecl::Items(items))
}

Ok(ConvertedDecl::Item(
static_def.static_item(new_name, ty, init),
))
}

Variable { .. } => Err(TranslationError::generic(
Expand Down Expand Up @@ -3577,52 +3575,73 @@ impl<'c> Translation<'c> {
val = self.volatile_read(val, qual_ty)?;
}

// If the variable is actually an `EnumConstant`, we need to add a cast to the
// expected integral type.
if let &CDeclKind::EnumConstant { .. } = decl {
val = self.convert_cast_from_enum(qual_ty.ctype, val)?;
}

// If we are referring to a function and need its address, we
// need to cast it to fn() to ensure that it has a real address.
let mut set_unsafe = false;
if ctx.needs_address() {
if let CDeclKind::Function { parameters, .. } = decl {
let ty = self.convert_type(qual_ty.ctype)?;
let actual_ty = self
.type_converter
.borrow_mut()
.knr_function_type_with_parameters(
&self.ast_context,
qual_ty.ctype,
parameters,
)?;
if let Some(actual_ty) = actual_ty {
if actual_ty != ty {
// If we're casting a concrete function to
// a K&R function pointer type, use transmute
self.import_type(qual_ty.ctype);

val = transmute_expr(actual_ty, ty, val);
set_unsafe = true;
}
} else {
let decl_kind = &self.ast_context[decl_id].kind;
let kind_with_declared_args =
self.ast_context.fn_decl_ty_with_declared_args(decl_kind);

if let Some(ty) = self
.ast_context
.type_for_kind(&kind_with_declared_args)
.map(CQualTypeId::new)
{
let ty = self.convert_type(ty.ctype)?;
val = mk().cast_expr(val, ty);

match decl {
CDeclKind::EnumConstant { .. } => {
// If the variable is actually an `EnumConstant`, we need to add a cast to
// the expected integral type.
val = self.convert_cast_from_enum(qual_ty.ctype, val)?;
}

CDeclKind::Function { parameters, .. } => {
// If we are referring to a function and need its address, we
// need to cast it to fn() to ensure that it has a real address.
if ctx.needs_address() {
let ty = self.convert_type(qual_ty.ctype)?;
let actual_ty = self
.type_converter
.borrow_mut()
.knr_function_type_with_parameters(
&self.ast_context,
qual_ty.ctype,
parameters,
)?;
if let Some(actual_ty) = actual_ty {
if actual_ty != ty {
// If we're casting a concrete function to
// a K&R function pointer type, use transmute
self.import_type(qual_ty.ctype);

val = transmute_expr(actual_ty, ty, val);
set_unsafe = true;
}
} else {
val = mk().cast_expr(val, ty);
let decl_kind = &self.ast_context[decl_id].kind;
let kind_with_declared_args =
self.ast_context.fn_decl_ty_with_declared_args(decl_kind);

if let Some(ty) = self
.ast_context
.type_for_kind(&kind_with_declared_args)
.map(CQualTypeId::new)
{
let ty = self.convert_type(ty.ctype)?;
val = mk().cast_expr(val, ty);
} else {
val = mk().cast_expr(val, ty);
}
}
}
}

CDeclKind::Variable {
has_static_duration,
has_thread_duration,
..
} => {
// Accessing a static variable is unsafe.
// In the current nightly, this applies also to taking a raw pointer,
// but this requirement was removed in later versions of the
// `raw_ref_op` feature.
if (*has_static_duration || *has_thread_duration)
&& (self.tcfg.edition < Edition2024 || !ctx.needs_address())
{
set_unsafe = true;
}
}

_ => {}
}

if let CTypeKind::VariableArray(..) =
Expand Down Expand Up @@ -4013,43 +4032,7 @@ impl<'c> Translation<'c> {

Paren(_, val) => self.convert_expr(ctx, val, override_ty),

CompoundLiteral(qty, val) => {
if !ctx.needs_address() || ctx.is_const {
// consts have their intermediates' lifetimes extended.
return self.convert_expr(ctx, val, override_ty);
}

// C compound literals are lvalues, but equivalent Rust expressions generally are not.
// So if an address is needed, store it in an intermediate variable first.
let fresh_name = self.renamer.borrow_mut().fresh();
let fresh_ty = self.convert_type(override_ty.unwrap_or(qty).ctype)?;

// Translate the expression to be assigned to the fresh variable.
// It will be assigned by value, so we don't need its address anymore.
let val = self.convert_expr(ctx.set_needs_address(false), val, override_ty)?;

val.and_then(|val| {
let fresh_stmt = {
let mutbl = if qty.qualifiers.is_const {
Mutability::Immutable
} else {
Mutability::Mutable
};

let local = mk().local(
mk().set_mutbl(mutbl).ident_pat(&fresh_name),
Some(fresh_ty),
Some(val),
);
mk().local_stmt(Box::new(local))
};

Ok(WithStmts::new(
vec![fresh_stmt],
mk().ident_expr(fresh_name),
))
})
}
CompoundLiteral(qty, val) => self.convert_compound_literal(ctx, qty, val, override_ty),

InitList(ty, ref ids, opt_union_field_id, _) => {
self.convert_init_list(ctx, ty, ids, opt_union_field_id)
Expand Down
6 changes: 1 addition & 5 deletions c2rust-transpile/src/translator/pointers.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -144,11 +144,7 @@ impl<'c> Translation<'c> {
// and must be regular-borrowed first.
// Borrowing in a const context will extend the lifetime to static.
else if arg_is_macro
|| ctx.is_const
&& matches!(
arg_expr_kind,
Some(CExprKind::Literal(..) | CExprKind::CompoundLiteral(..))
)
|| ctx.is_const && matches!(arg_expr_kind, Some(CExprKind::Literal(..)))
{
let arg_cty_kind = &self.ast_context.resolve_type(arg_cty.ctype).kind;

Expand Down
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