From 5e01a76097265f4bb27b18885b9af3f2778180f9 Mon Sep 17 00:00:00 2001
From: John Hodge <tpg@mutabah.net>
Date: Tue, 17 Dec 2024 12:13:04 +0800
Subject: [PATCH] HIR Typecheck - Properly pass type params to const evaluation
 (re #322)

---
 samples/test/mrustc-322.rs           | 14 +++++++++++++
 src/hir_conv/constant_evaluation.cpp | 30 ++++++++++++++++++++++++++--
 src/hir_typeck/expr_cs.cpp           |  1 +
 3 files changed, 43 insertions(+), 2 deletions(-)
 create mode 100644 samples/test/mrustc-322.rs

diff --git a/samples/test/mrustc-322.rs b/samples/test/mrustc-322.rs
new file mode 100644
index 000000000..654f3ef71
--- /dev/null
+++ b/samples/test/mrustc-322.rs
@@ -0,0 +1,14 @@
+// ignore-test - Rustc doesn't allow this, plus it doesn't specify the type for the `Vec<_>`
+#![crate_type = "lib"]
+struct Assert<const COND: bool>;
+trait IsTrue {}
+impl IsTrue for Assert<true> {}
+trait IsNotZst {}
+impl<T> IsNotZst for T
+where
+    Assert<{ std::mem::size_of::<T>() > 0 }>: IsTrue,
+{}
+fn assert_not_zero_sized<T: IsNotZst>(_: T) {}
+fn main() {
+    assert_not_zero_sized(vec![]);
+}
diff --git a/src/hir_conv/constant_evaluation.cpp b/src/hir_conv/constant_evaluation.cpp
index 77d0e25a1..9ae986043 100644
--- a/src/hir_conv/constant_evaluation.cpp
+++ b/src/hir_conv/constant_evaluation.cpp
@@ -3729,6 +3729,22 @@ void ConvertHIR_ConstantEvaluate_ArraySize(const Span& sp, const ::HIR::Crate& c
     }
 }
 
+namespace {
+    bool params_contain_ivars(const ::HIR::PathParams& params) {
+        for(const auto& t : params.m_types) {
+            if( visit_ty_with(t, [](const HIR::TypeRef& t){ return t.data().is_Infer(); })) {
+                return true;
+            }
+        }
+        for(const auto& v : params.m_values) {
+            if( v.is_Infer() ) {
+                return true;
+            }
+        }
+        return false;
+    }
+}
+
 void ConvertHIR_ConstantEvaluate_MethodParams(
     const Span& sp,
     const ::HIR::Crate& crate, const HIR::SimplePath& mod_path, const ::HIR::GenericParams* impl_generics, const ::HIR::GenericParams* item_generics,
@@ -3740,7 +3756,8 @@ void ConvertHIR_ConstantEvaluate_MethodParams(
     {
         if(v.is_Unevaluated())
         {
-            const auto& e = *v.as_Unevaluated()->expr;
+            const auto& ue = *v.as_Unevaluated();
+            const auto& e = *ue.expr;
             auto name = FMT("param_" << &v << "#");
             TRACE_FUNCTION_FR(name, name);
             auto nvs = NewvalState { crate.get_mod_by_path(Span(), mod_path), mod_path, name };
@@ -3751,12 +3768,21 @@ void ConvertHIR_ConstantEvaluate_MethodParams(
             // - Which, might not be known at this point - might be a UfcsInherent
             try
             {
+                // TODO: if there's an ivar in the param list, then throw defer
+                // - Caller should ensure that known ivars are expanded.
+                if( params_contain_ivars(ue.params_impl) || params_contain_ivars(ue.params_item) ) {
+                    throw Defer();
+                }
+
                 auto idx = static_cast<size_t>(&v - &params.m_values.front());
                 ASSERT_BUG(sp, idx < params_def.m_values.size(), "");
                 const auto& ty = params_def.m_values[idx].m_type;
                 ASSERT_BUG(sp, !monomorphise_type_needed(ty), "" << ty);
+                MonomorphState  ms;
+                ms.pp_impl = &ue.params_impl;
+                ms.pp_method = &ue.params_item;
 
-                auto val = eval.evaluate_constant( ::HIR::ItemPath(mod_path, name.c_str()), e, ty.clone() );
+                auto val = eval.evaluate_constant( ::HIR::ItemPath(mod_path, name.c_str()), e, ty.clone(), std::move(ms) );
                 v = ::HIR::ConstGeneric::make_Evaluated(std::move(val));
             }
             catch(const Defer& )
diff --git a/src/hir_typeck/expr_cs.cpp b/src/hir_typeck/expr_cs.cpp
index 637542077..02b333bdc 100644
--- a/src/hir_typeck/expr_cs.cpp
+++ b/src/hir_typeck/expr_cs.cpp
@@ -2385,6 +2385,7 @@ void Context::equate_values(const Span& sp, const ::HIR::ConstGeneric& rl, const
                 this->m_ivars.set_ivar_val_to(r.as_Infer().index, l.clone());
             }
             else {
+                // TODO: What about unevaluated values due to type inference?
                 ERROR(sp, E0000, "Value mismatch between " << l << " and " << r);
             }
         }