fix(0118): cast accepts compound type args; compound type literals are first-class Type values

examples/0182-types-cast-compound-types.sx

@@ -0,0 +1,27 @@
+// `cast(T) expr` accepts any compile-time-resolvable type argument,
+// including compound shapes: `*T`, `[*]T`, `?T`, `[]T`. The same lowering
+// makes a compound type literal a first-class `Type` value in expression
+// position (`t : Type = *s64;`), mirroring named types (`t : Type = f64;`).
+// Regression (issue 0118): compound casts fell into the runtime-dispatch
+// path and died with "unresolved 'unknown_expr'".
+
+#import "modules/std.sx";
+
+main :: () {
+    x := 42;
+    p : *s64 = @x;
+    q : *s64 = cast(*s64) p;        // no-op pointer cast
+    print("a: {}\n", q.*);
+    addr : s64 = xx p;
+    r : *s64 = cast(*s64) addr;     // int → ptr through compound cast
+    print("b: {}\n", r.*);
+    mp : [*]s64 = cast([*]s64) p;   // ptr → many-pointer
+    print("c: {}\n", mp[0]);
+    o : ?s32 = cast(?s32) 7;        // optional wrap
+    print("d: {}\n", o ?? -1);
+    arr := .[1, 2, 3];
+    s : []s64 = cast([]s64) arr;    // array → slice
+    print("e: {} {}\n", s.len, s[2]);
+    t : Type = *s64;                // first-class compound Type value
+    print("f: {}\n", type_name(t));
+}

examples/expected/0182-types-cast-compound-types.exit

@@ -0,0 +1 @@
+0

examples/expected/0182-types-cast-compound-types.stderr

@@ -0,0 +1 @@
+

examples/expected/0182-types-cast-compound-types.stdout

@@ -0,0 +1,6 @@
+a: 42
+b: 42
+c: 42
+d: 7
+e: 3 3
+f: *s64

issues/0118-cast-compound-type-arg-unresolved.md

@@ -1,5 +1,20 @@
 # 0118 — `cast(<compound type>) expr` dies with "unresolved 'unknown_expr'"
 
+> **RESOLVED** (2026-06-11, same session, Agra-authorized in-session fix).
+> Two-part root cause: (1) `lowerCall` lowers args BEFORE the cast handler,
+> and compound type literals had NO expression-position lowering — they hit
+> `lowerExpr`'s catch-all `unknown_expr` error. Fixed by giving the six
+> compound type-expr shapes (`*T`, `[*]T`, `[]T`, `?T`, `[N]T`, fn types) a
+> first-class `const_type` lowering arm in `src/ir/lower/expr.zig`,
+> mirroring named types (`t : Type = *s64;` now works like `t : Type =
+> f64;`). (2) The cast handler's private static-type gate only accepted
+> bare names — replaced with the canonical `isStaticTypeArg`
+> (`src/ir/lower/call.zig`), so static compound casts route through
+> `coerceExplicit` while the runtime-`Type`-variable form (`cast(type) val`
+> in category arms) still falls through to runtime dispatch. Regression
+> test: examples/0182-types-cast-compound-types.sx (all compound cast
+> forms + the first-class Type value). Suite 579/579.
+
 ## Symptom
 
 `cast(T) expr` with a COMPOUND static type argument (`*s64`, `[]u8`, `?s32`,

src/ir/lower/call.zig

@@ -387,25 +387,16 @@ pub fn lowerCall(self: *Lowering, c_in: *const ast.Call) Ref {
             };
 
             // Handle cast(TargetType, val) — emit conversion instructions
-            // Only for compile-time known types (type_expr or known type names)
+            // for any compile-time-resolvable type argument. The gate is the
+            // canonical `isStaticTypeArg` (the one `type_name`/`type_eq` use),
+            // so compound shapes (`*T`, `[]T`, `?T`, `[*]T`, `[N]T`) resolve
+            // statically instead of falling into the runtime-dispatch path
+            // and dying unresolved (issue 0118). An identifier bound in scope
+            // as a runtime `Type` value (the `cast(type) val` category-arm
+            // form) still classifies as non-static and falls through.
             if (std.mem.eql(u8, id.name, "cast") and c.args.len >= 2) {
                 const type_arg = c.args[0];
-                const is_static_type = blk: {
-                    if (type_arg.data == .type_expr) break :blk true;
-                    if (type_arg.data == .identifier) {
-                        const tname = type_arg.data.identifier.name;
-                        // Check if it's a known type name (not a runtime variable)
-                        if (type_bridge.resolveTypePrimitive(tname) != null) break :blk true;
-                        if (self.type_bindings) |bindings| {
-                            if (bindings.get(tname) != null) break :blk true;
-                        }
-                        // Check if it's a registered struct/enum type name
-                        const name_id = self.module.types.internString(tname);
-                        if (self.module.types.findByName(name_id) != null) break :blk true;
-                    }
-                    break :blk false;
-                };
-                if (is_static_type) {
+                if (self.isStaticTypeArg(type_arg)) {
                     const dst_ty = self.resolveTypeArg(c.args[0]);
                     const val = args.items[1]; // already lowered
                     const src_ty = self.inferExprType(c.args[1]);

src/ir/lower/expr.zig

@@ -2021,6 +2021,25 @@ pub fn lowerExpr(self: *Lowering, node: *const Node) Ref {
             break :blk self.emitError(te.name, node.span);
         },
 
+        // Compound type literals (`*T`, `[]T`, `[*]T`, `?T`, `[N]T`, fn types)
+        // in expression position are first-class `Type` values, exactly like
+        // the named form above (`t : Type = *s64;` ↔ `t : Type = f64;`). Also
+        // the path a static `cast(*s64) v` type argument takes — call args are
+        // lowered before the cast handler inspects the AST (issue 0118).
+        .pointer_type_expr,
+        .many_pointer_type_expr,
+        .slice_type_expr,
+        .optional_type_expr,
+        .array_type_expr,
+        .function_type_expr,
+        => blk: {
+            const ty = self.resolveTypeWithBindings(node);
+            // The resolver diagnosed any unresolved leaf; don't mint a Type
+            // value around the failure sentinel.
+            if (ty == .unresolved) break :blk self.emitError("unknown_expr", node.span);
+            break :blk self.builder.constType(ty);
+        },
+
         .try_expr => |te| self.lowerTry(te.operand, node.span),
         .catch_expr => |ce| self.lowerCatch(&ce, node.span),
         .caller_location => self.lowerCallerLocation(node),