librustc: Implement tuple struct constants. r=brson

Author: pcwalton

src/librustc/middle/check_const.rs

@@ -95,19 +95,36 @@ fn check_expr(sess: Session, def_map: resolve::DefMap,
             match def_map.find(e.id) {
               Some(def_const(def_id)) |
                 Some(def_fn(def_id, _)) |
-                Some(def_variant(_, def_id)) => {
+                Some(def_variant(_, def_id)) |
+                Some(def_class(def_id)) => {
                 if !ast_util::is_local(def_id) {
                     sess.span_err(
                         e.span, ~"paths in constants may only refer to \
-                                 crate-local constants or functions");
+                                 crate-local constants, functions, or \
+                                 structs");
                 }
               }
-              _ => {
+              Some(def) => {
+                debug!("(checking const) found bad def: %?", def);
                 sess.span_err(
                     e.span,
-                    ~"paths in constants may only refer to \
-                      constants or functions");
+                    fmt!("paths in constants may only refer to \
+                          constants or functions"));
               }
+              None => {
+                sess.span_bug(e.span, ~"unbound path in const?!");
+              }
+            }
+          }
+          expr_call(callee, _, false) => {
+            match def_map.find(callee.id) {
+                Some(def_class(*)) => {}    // OK.
+                _ => {
+                    sess.span_err(
+                        e.span,
+                        ~"function calls in constants are limited to \
+                          structure constructors");
+                }
             }
           }
           expr_paren(e) => { check_expr(sess, def_map, method_map,

src/librustc/middle/trans/consts.rs

@@ -416,7 +416,22 @@ fn const_expr(cx: @crate_ctxt, e: @ast::expr) -> ValueRef {
             }
         }
       }
-        ast::expr_paren(e) => { return const_expr(cx, e); }
+      ast::expr_call(callee, args, _) => {
+        match cx.tcx.def_map.find(callee.id) {
+            Some(ast::def_class(def_id)) => {
+                let ety = ty::expr_ty(cx.tcx, e);
+                let llty = type_of::type_of(cx, ety);
+                let llstructbody = C_struct(args.map(|a| const_expr(cx, *a)));
+                if ty::ty_dtor(cx.tcx, def_id).is_present() {
+                    C_named_struct(llty, ~[ llstructbody, C_u8(0) ])
+                } else {
+                    C_named_struct(llty, ~[ llstructbody ])
+                }
+            }
+            _ => cx.sess.span_bug(e.span, ~"expected a struct def")
+        }
+      }
+      ast::expr_paren(e) => { return const_expr(cx, e); }
       _ => cx.sess.span_bug(e.span,
             ~"bad constant expression type in consts::const_expr")
     };

src/test/run-pass/const-tuple-struct.rs

@@ -0,0 +1,13 @@
+struct Bar(int, int);
+
+const X: Bar = Bar(1, 2);
+
+fn main() {
+    match X {
+        Bar(x, y) => {
+            assert x == 1;
+            assert y == 2;
+        }
+    }
+}
+