First declosure impl

compiler/src/declass/step_1.rs

@@ -10,6 +10,9 @@
 //! `get_field "prototype" ; put_field @meth`; the field-initialiser tail is
 //! dropped. Detection (`find_class_seqs`) records the ranges; replacement
 //! (`ClassSequence::emit_prototype`) reads operands out of each matched range.
+//!
+//! Derived classes (`extends`) are unsupported and panic: prototype form would
+//! have to flatten the parent's prototype in and lower `super`.
 
 use std::range::Range;
 
@@ -160,6 +163,16 @@ fn find_class_seqs(mut ins: &[RegInstr]) -> Vec<ClassSequence> {
 
 fn match_class_seq(ins: &[RegInstr]) -> Result<(&[RegInstr], usize), &[RegInstr]> {
     let ins = match_one(ins, |i| i.op == OpCode::PushConst8)?;
+
+    // A class build is `push_const8 ; define_class`. Derived classes (`extends`)
+    // are unsupported: prototype form would have to flatten the parent's
+    // prototype in and lower `super`, neither of which is implemented.
+    if let Some(i) = ins.first() {
+        if i.op == OpCode::DefineClass && is_derived(i) {
+            panic!("declass: derived classes (extends) are not supported");
+        }
+    }
+
     let ins = match_one(ins, |i| i.op == OpCode::DefineClass)?;
     let (ins, num_methods) = match_many(ins, match_method_seq);
     let ins = match_opt(ins, match_field_init_seq);
@@ -167,6 +180,15 @@ fn match_class_seq(ins: &[RegInstr]) -> Result<(&[RegInstr], usize), &[RegInstr]
     Ok((ins, num_methods))
 }
 
+/// A derived class: `define_class` with the derived flag set.
+fn is_derived(i: &RegInstr) -> bool {
+    matches!(i.imm, ImmOperand::AtomU8 { arg, .. } if arg & 1 == 1)
+}
+
+// TODO: accessors are not handled. A getter/setter is a `define_method` with a
+// non-zero kind in `arg`; this matcher takes it for an ordinary method, so it
+// is wrongly lowered to a `put_field` (a data property) instead of an accessor
+// property. It should instead make the whole class pass through untouched.
 fn match_method_seq(ins: &[RegInstr]) -> Result<&[RegInstr], &[RegInstr]> {
     let ins = match_one(ins, |i| i.op == OpCode::Fclosure8)?;
     let ins = match_one(ins, |i| i.op == OpCode::DefineMethod)?;
@@ -177,7 +199,12 @@ fn match_field_init_seq(ins: &[RegInstr]) -> Result<&[RegInstr], &[RegInstr]> {
     let is_put_loc = |op| {
         matches!(
             op,
-            OpCode::PutLoc | OpCode::PutLoc0 | OpCode::PutLoc1 | OpCode::PutLoc2 | OpCode::PutLoc3
+            OpCode::PutLoc
+                | OpCode::PutLoc8
+                | OpCode::PutLoc0
+                | OpCode::PutLoc1
+                | OpCode::PutLoc2
+                | OpCode::PutLoc3
         )
     };