refactor: 拆分 statement emit 分发逻辑

crates/oxide_compiler/src/emitter/stmt/switch.rs

@@ -0,0 +1,50 @@
+use super::*;
+
+impl Compiler {
+    pub(in crate::emitter) fn emit_switch_statement(
+        &self, stmt: &Statement, ctx: &mut CompileCtx,
+    ) -> Result<Option<u8>, String> {
+        let Statement::SwitchStatement(sw) = stmt else {
+            return Ok(None);
+        };
+        let id = ctx.next_label_id();
+        let end_label = Label::SwitchEnd(id);
+        ctx.push_switch(end_label);
+
+        let disc_reg = self.emit_expression(&sw.discriminant, ctx)?;
+        let compare_reg_checkpoint = ctx.reg_checkpoint();
+        let cases = &sw.cases;
+
+        for (case_idx, case) in cases.iter().enumerate() {
+            if let Some(test) = &case.test {
+                let test_reg = self.emit_expression(test, ctx)?;
+                let eq_reg = ctx.alloc_reg();
+                ctx.emit(opcode::encode(OpCode::EQ, eq_reg, disc_reg, test_reg));
+
+                let case_label = Label::SwitchCase(id, case_idx as u32);
+                let body_pos = ctx.resolve_label(case_label)?;
+                let offset = (body_pos as isize) - (ctx.bytecode.len() as isize);
+                let offset = ctx.checked_jump_offset(offset);
+                ctx.emit(opcode::encode_jmp_if_true(eq_reg, offset));
+                ctx.restore_reg_checkpoint(compare_reg_checkpoint);
+            }
+        }
+
+        let has_default = cases.iter().any(|c| c.test.is_none());
+        if !has_default {
+            let end_pos = ctx.resolve_label(end_label)?;
+            let offset = (end_pos as isize) - (ctx.bytecode.len() as isize);
+            let offset = ctx.checked_jump_offset(offset);
+            ctx.emit(opcode::encode_jmp(offset));
+        }
+
+        for case in cases.iter() {
+            for s in &case.consequent {
+                self.emit_statement(s, ctx)?;
+            }
+        }
+
+        ctx.pop_switch();
+        Ok(None)
+    }
+}