[Sema] be more descriptive when hardening fails

Author: isuckatcs

src/sema.cpp

@@ -1085,12 +1085,16 @@ Sema::hardenTypeIfNeeded(res::Context &ctx, res::Expr *expr, res::Type *to) {
   if (!fromInner || !toInner)
     return expr;
 
-  if (!ctx.canUnify(fromInner, toInner))
+  if (!toInner->getAs<res::UninferredType>() &&
+      !ctx.canUnify(fromInner, toInner))
     return expr;
 
-  ctx.unify(fromInner, toInner);
   auto *harden = res::ImplicitHardening::create(ctx, expr->location, expr);
-  harden->setType(to);
+  if (to->getAs<res::PointerType>())
+    harden->setType(res::PointerType::create(ctx, fromInner, false));
+  else
+    harden->setType(res::RefType::create(ctx, fromInner, false));
+
   return harden;
 }
 

test/sema/qualification_conversion_requirement_not_satisfied.yl

@@ -0,0 +1,15 @@
+// RUN: compiler %s -res-dump 2>&1 | filecheck %s
+trait A {
+  fn foo(self: &Self);
+}
+
+fn foo<T : A>(t: &T) {
+  t.foo();
+}
+
+fn bar(mn: &mut number) {
+  // CHECK: [[# @LINE + 1 ]]:7: error: cannot satisfy requirement 'number : A'
+  foo(mn);
+}
+
+fn main() {}

test/sema/qualification_conversion_requirement_not_satisfied_ptr.yl

@@ -0,0 +1,14 @@
+// RUN: compiler %s -res-dump 2>&1 | filecheck %s
+trait A {
+  fn foo(self: &Self);
+}
+
+fn foo<T : A>(t: *T) {
+  t.foo();
+}
+
+fn main() {
+  let p = gc mut 123;
+  // CHECK: [[# @LINE + 1 ]]:7: error: cannot satisfy requirement 'number : A'
+  foo(p);
+}