feat: check placeholders inside unchecked blocks (#172)

* feat/check-placeholders-inside-unchecked

* fix

crates/sema/src/ast_passes.rs

@@ -208,6 +208,12 @@ impl<'ast> Visit<'ast> for AstValidator<'_, 'ast> {
                         .span(stmt.span)
                         .emit();
                 }
+                if self.in_unchecked_block {
+                    self.dcx()
+                        .err("placeholder statements cannot be used inside unchecked blocks")
+                        .span(stmt.span)
+                        .emit();
+                }
             }
             _ => {}
         }

tests/ui/resolve/placeholder_unchecked.sol

@@ -0,0 +1,9 @@
+contract A {
+    modifier xrp() {
+        unchecked {
+            _; //~ERROR: placeholder statements cannot be used inside unchecked blocks
+        }
+    }
+
+    constructor() {}
+}

tests/ui/resolve/placeholder_unchecked.stderr

@@ -0,0 +1,9 @@
+error: placeholder statements cannot be used inside unchecked blocks
+  --> ROOT/tests/ui/resolve/placeholder_unchecked.sol:LL:CC
+   |
+LL |             _;
+   |             ^^
+   |
+
+error: aborting due to 1 previous error
+