AIGEN: Fix #988: Forbid underscore-prefixed variable values

skiplang/cli/src/usage.sk

@@ -85,11 +85,11 @@ private fun usageOptions(options: Sequence<Cli.Arg>): String {
       | _ -> `    --${arg.name}`
       };
       optFlags = arg match {
-      | Cli.ValuedArg{_value_name} ->
+      | Cli.ValuedArg{_value_name => value_name} ->
         if (arg._repeatable) {
-          `${baseOptFlags} [<${_value_name}>]`
+          `${baseOptFlags} [<${value_name}>]`
         } else {
-          `${baseOptFlags} <${_value_name}>`
+          `${baseOptFlags} <${value_name}>`
         }
       | _ if (arg._repeatable) -> `${baseOptFlags}...`
       | _ -> baseOptFlags
@@ -144,8 +144,11 @@ fun usage(
   values = cmd._args.filterMap(
     (arg ->
       (arg match {
-      | ValuedArg{_value_name, _value_about} if (_value_about.size() > 0) ->
-        Some((_value_name, _value_about))
+      | ValuedArg{
+        _value_name => value_name,
+        _value_about => value_about,
+      } if (value_about.size() > 0) ->
+        Some((value_name, value_about))
       | _ -> None()
       })),
   );

skiplang/compiler/src/convertTree.sk

@@ -1383,27 +1383,27 @@ class Converter{file: FileCache.InputSource} {
           range,
           SkipAst.Pat_type(
             SkipAst.Tid_object(SkipAst.Tclass((range, "Success"))),
-            Some(Positional(Array[(range, SkipAst.Pat_var((range, "__x")))])),
+            Some(Positional(Array[(range, SkipAst.Pat_var((range, "!x")))])),
             SkipAst.Complete(),
           ),
         ),
       ],
       None(),
-      (range, SkipAst.Var((range, "__x"))),
+      (range, SkipAst.Var((range, "!x"))),
     );
     early_return_branch = (
       List[
         (
           range,
           SkipAst.Pat_type(
             SkipAst.Tid_object(SkipAst.Tclass((range, "Failure"))),
-            Some(Positional(Array[(range, SkipAst.Pat_var((range, "__x")))])),
+            Some(Positional(Array[(range, SkipAst.Pat_var((range, "!x")))])),
             SkipAst.Complete(),
           ),
         ),
       ],
       None(),
-      (range, SkipAst.Return((range, SkipAst.Var((range, "__x"))))),
+      (range, SkipAst.Return((range, SkipAst.Var((range, "!x"))))),
     );
 
     SkipAst.Match(

skiplang/compiler/src/skipNaming.sk

@@ -439,9 +439,8 @@ fun pattern_bindings(acc: UMap<void>, pat: A.Pattern): UMap<void> {
   }
 }
 
-// TODO consider !name.i1.startsWith("_")
 fun bind_pattern_name(acc: UMap<void>, name: A.Name): UMap<void> {
-  if (name.i1 != "_") acc.add(name, void) else acc
+  if (!name.i1.startsWith("_")) acc.add(name, void) else acc
 }
 
 fun bind_pattern_params(
@@ -940,14 +939,15 @@ fun check_locals_pattern(bound: Bound, pat: N.Pattern): Bound {
   | N.Pat_const _
   | N.Pat_literal _ ->
     bound
-  | N.Pat_var(var_name) -> bound.bind(var_name)
+  | N.Pat_var(var_name) ->
+    if (is_wildcard_name(var_name)) bound else bound.bind(var_name)
   | N.Pat_type(_, obj_params, _) ->
     obj_params match {
     | None() -> bound
     | Some(params) -> params.foldl(check_locals_pattern, bound)
     }
   | N.Pat_as(p, var_name) ->
-    !bound = bound.bind(var_name);
+    !bound = if (is_wildcard_name(var_name)) bound else bound.bind(var_name);
     check_locals_pattern(bound, p)
   }
 }

skiplang/compiler/src/skipOuterIstUtils.sk

@@ -1544,7 +1544,7 @@ fun binding_needs_ref(binding: O.BindingInfo): Bool {
 }
 
 fun is_underscore_binding(b: O.Binding): Bool {
-  b.name.id == "_"
+  b.name.id.startsWith("_")
 }
 
 /* parameters */

skiplang/compiler/tests/syntax/invalid/under_ident_3.exp

@@ -0,0 +1 @@
+

skiplang/compiler/tests/syntax/invalid/under_ident_3.exp_err

@@ -0,0 +1,7 @@
+File "tests/syntax/invalid/under_ident_3.sk", line 10, characters 7-8:
+You cannot use a variable that starts with _
+ 8 |     | T1(_x, _y, _)
+ 9 |     | T2(_x, _y, _) ->
+10 |       _x + _y
+   |       ^^
+11 |     }

skiplang/compiler/tests/syntax/invalid/under_ident_3.sk

@@ -0,0 +1,18 @@
+base class T {
+  children =
+  | T1(x: Int, y: Int, z: Int)
+  | T2(x: Int, y: Int, z: String)
+
+  fun broken(): Int {
+    this match {
+    | T1(_x, _y, _)
+    | T2(_x, _y, _) ->
+      _x + _y
+    }
+  }
+}
+
+fun main(): void {
+  t2 = T2(1, 2, "three");
+  print_string(t2.broken().toString())
+}

skiplang/compiler/tests/syntax/invalid/under_ident_7.exp_err

@@ -1,7 +1,7 @@
-File "tests/syntax/invalid/under_ident_7.sk", line 4, characters 11-11:
-Unbound name: _
+File "tests/syntax/invalid/under_ident_7.sk", line 4, characters 22-22:
+You cannot use a variable that starts with _
 2 |   fun matcher(): T {
 3 |     this match {
 4 |     | Foo{_ => _} -> _
-  |           ^
+  |                      ^
 5 |     }