MIR Gen - Rough support for Box

3 files changed, 49 insertions, 3 deletions

diff --git a/src/mir/from_hir.cpp b/src/mir/from_hir.cpp
index 4a540c14..5a0ca03a 100644
--- a/src/mir/from_hir.cpp
+++ b/src/mir/from_hir.cpp
@@ -929,7 +929,13 @@ namespace {
             }
             else
             {
-                TODO(node.span(), "Support emitting CoerceUnsized-based _Unsize ops in MIR - " << ty_in << "  ->  " << ty_out);
+                // NOTES: (from IRC: eddyb)
+                // < eddyb> they're required that T and U are the same struct definition (with different type parameters) and exactly one field differs in type between T and U (ignoring PhantomData)
+                // < eddyb> Mutabah: I forgot to mention that the field that differs in type must also impl CoerceUnsized
+
+                // TODO: Just emit a cast and leave magic handling to codegen
+                // - This code _could_ do inspection of the types and insert a destructure+unsize+restructure, but that does't handle direct `T: CoerceUnsize<U>`
+                m_builder.set_result( node.span(), ::MIR::RValue::make_Cast({ mv$(ptr_lval), node.m_res_type.clone() }) );
             }
         }
         void visit(::HIR::ExprNode_Index& node) override
@@ -1002,13 +1008,25 @@ namespace {
             
             TU_MATCH_DEF( ::HIR::TypeRef::Data, (ty_val.m_data), (te),
             (
+                if( m_builder.lang_Box() )
+                {
+                    if( ty_val.m_data.is_Path()
+                     && ty_val.m_data.as_Path().path.m_data.is_Generic()
+                     && ty_val.m_data.as_Path().path.m_data.as_Generic().m_path == *m_builder.lang_Box()
+                        )
+                    {
+                        // Box magically derefs.
+                        // HACK: Break out of the switch used for TU_MATCH_DEF
+                        break;
+                    }
+                }
                 BUG(sp, "Deref on unsupported type - " << ty_val);
                 ),
-            //(Array,
-            //    ),
             (Pointer,
+                // Deref on a pointer - TODO: Requires unsafe
                 ),
             (Borrow,
+                // Deref on a borrow - Always valid... assuming borrowck is there :)
                 )
             )
             
diff --git a/src/mir/from_hir.hpp b/src/mir/from_hir.hpp
index c5106bd0..1f9007a5 100644
--- a/src/mir/from_hir.hpp
+++ b/src/mir/from_hir.hpp
@@ -78,6 +78,8 @@ class MirBuilder
     const ::HIR::Function::args_t&  m_args;
     ::MIR::Function&    m_output;
     
+    const ::HIR::SimplePath*    m_lang_Box;
+    
     unsigned int    m_current_block;
     bool    m_block_active;
     
@@ -111,6 +113,7 @@ public:
     MirBuilder(const Span& sp, const StaticTraitResolve& resolve, const ::HIR::Function::args_t& args, ::MIR::Function& output);
     ~MirBuilder();
     
+    const ::HIR::SimplePath* lang_Box() const { return m_lang_Box; }
     const ::HIR::Crate& crate() const { return m_resolve.m_crate; }
     
     // - Values
diff --git a/src/mir/mir_builder.cpp b/src/mir/mir_builder.cpp
index 89141042..eb40f58b 100644
--- a/src/mir/mir_builder.cpp
+++ b/src/mir/mir_builder.cpp
@@ -16,10 +16,15 @@ MirBuilder::MirBuilder(const Span& sp, const StaticTraitResolve& resolve, const
     m_resolve(resolve),
     m_args(args),
     m_output(output),
+    m_lang_Box(nullptr),
     m_block_active(false),
     m_result_valid(false),
     m_fcn_scope(*this, 0)
 {
+    if( resolve.m_crate.m_lang_items.count("owned_box") > 0 ) {
+        m_lang_Box = &resolve.m_crate.m_lang_items.at("owned_box");
+    }
+    
     set_cur_block( new_bb_unlinked() );
     m_scopes.push_back( ScopeDef { sp } );
     m_scope_stack.push_back( 0 );
@@ -652,6 +657,25 @@ void MirBuilder::with_val_type(const Span& sp, const ::MIR::LValue& val, ::std::
             (
                 BUG(sp, "Deref on unexpected type - " << ty);
                 ),
+            (Path,
+                if( m_lang_Box )
+                {
+                    TU_IFLET( ::HIR::Path::Data, te.path.m_data, Generic, e,
+                        if( e.m_path == *m_lang_Box ) {
+                            cb( e.m_params.m_types.at(0) );
+                        }
+                        else {
+                            BUG(sp, "Deref on unexpected type - " << ty);
+                        }
+                    )
+                    else {
+                        BUG(sp, "Deref on unexpected type - " << ty);
+                    }
+                }
+                else {
+                    BUG(sp, "Deref on unexpected type - " << ty);
+                }
+                ),
             (Pointer,
                 cb(*te.inner);
                 ),
@@ -910,6 +934,7 @@ void MirBuilder::moved_lvalue(const Span& sp, const ::MIR::LValue& lv)
         if( lvalue_is_copy(sp, lv) ) {
         }
         else {
+            // TODO: Move out of owned_box _is_ valid, and marks the box slot for shallow drop
             BUG(sp, "Move out of deref with non-Copy values - &move? - " << lv);
             moved_lvalue(sp, *e.val);
         }