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Improve error when trying to use an extern const as a compile time constant. #2969

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This commit is contained in:
Christoffer Lerno
2026-02-23 19:15:23 +01:00
parent 8373ab0509
commit 0ed917cdc2
4 changed files with 42 additions and 3 deletions
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1
releasenotes.md
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@@ -20,6 +20,7 @@
- Constdef declarations introduced.
- Properly support `@deprecated` as contract.
- Support deprecating enum values.
- Improve error when trying to use an extern const as a compile time constant. #2969
### Stdlib changes
- Summarize sort macros as generic function wrappers to reduce the amount of generated code. #2831

18
src/compiler/sema_decls.c
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@@ -4707,6 +4707,20 @@ static bool sema_analyse_variable_type(SemaContext *context, Type *type, SourceS
UNREACHABLE
}
INLINE void sema_error_not_constant(SemaContext *context, Decl *target, Expr *init)
{
if (init->expr_kind == EXPR_IDENTIFIER)
{
Decl *decl = init->ident_expr;
if (decl->decl_kind == DECL_VAR && decl->var.kind == VARDECL_CONST && decl->is_extern)
{
SEMA_ERROR(init, "%s must be assigned a compile-time constant. 'extern' constants are resolved at link time and therefore are not compile-time values.", target->name);
return;
}
}
SEMA_ERROR(init, "Expected a compile time constant value assigned to %s.", target->name);
}
/**
* Analyse $foo and $Foo variables.
*/
@@ -4792,7 +4806,7 @@ bool sema_analyse_var_decl_ct(SemaContext *context, Decl *decl, bool *check_defi
if (!expr_is_runtime_const(init))
{
if (check_defined) goto FAIL_CHECK;
SEMA_ERROR(init, "Expected a constant expression assigned to %s.", decl->name);
sema_error_not_constant(context, decl, init);
goto FAIL;
}
break;
@@ -4811,7 +4825,7 @@ bool sema_analyse_var_decl_ct(SemaContext *context, Decl *decl, bool *check_defi
if (!expr_is_runtime_const(init))
{
if (check_defined) goto FAIL_CHECK;
SEMA_ERROR(init, "Expected a constant expression assigned to %s.", decl->name);
sema_error_not_constant(context, decl, init);
goto FAIL;
}
// Update the type.

10
src/compiler/sema_expr.c
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@@ -1679,7 +1679,15 @@ static bool sema_analyse_parameter(SemaContext *context, Expr *arg, Decl *param,
{
RETURN_SEMA_FUNC_ERROR(definition, arg, "This method is only valid on a compile time constant value.");
}
RETURN_SEMA_FUNC_ERROR(definition, arg, "A compile time parameter must always be a constant, did you mistake it for a normal parameter?");
if (arg->expr_kind == EXPR_IDENTIFIER)
{
Decl *decl = arg->ident_expr;
if (decl->decl_kind == DECL_VAR && decl->var.kind == VARDECL_CONST && decl->is_extern)
{
RETURN_SEMA_FUNC_ERROR(definition, arg, "A compile-time parameter requires a value known at compile time. Did you mistake if for a regular parameter? 'extern' constants are not compile-time constants.");
}
}
RETURN_SEMA_FUNC_ERROR(definition, arg, "A compile time parameter must always be a compile-time constant value, did you mistake it for a regular parameter?");
}
break;
case VARDECL_PARAM_CT_TYPE:

16
test/test_suite/compile_time/extern_is_not_const.c3 Normal file
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@@ -0,0 +1,16 @@
module test;
import std;
extern const void* FOO @cname("malloc");
macro foo($x) {}
fn void test()
{
var $x = FOO; // #error: $x must be assigned a compile-time constant. 'extern' constants are resolved
}
fn void test2()
{
foo(FOO); // #error: $x must be assigned a compile-time constant. 'extern' constants are resolved
}