From d2796697427df6ef8c7ddc6e1ae366ccae4ffcea Mon Sep 17 00:00:00 2001
From: Patrick Walton <pcwalton@mimiga.net>
Date: Mon, 10 Dec 2012 13:04:04 -0800
Subject: [PATCH] libsyntax: Implement `deriving` for struct-like enum variants

---
 src/libsyntax/ext/build.rs                    |  8 +++
 src/libsyntax/ext/deriving.rs                 | 64 ++++++++++++++-----
 ...-via-extension-struct-like-enum-variant.rs | 12 ++++
 3 files changed, 68 insertions(+), 16 deletions(-)
 create mode 100644 src/test/run-pass/deriving-via-extension-struct-like-enum-variant.rs

diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index 04a59d1fe4162..89a87ebd5e853 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -219,6 +219,14 @@ fn mk_pat_enum(cx: ext_ctxt,
     let pat = ast::pat_enum(path, Some(move subpats));
     mk_pat(cx, span, move pat)
 }
+fn mk_pat_struct(cx: ext_ctxt,
+                 span: span,
+                 path: @ast::path,
+                 +field_pats: ~[ast::field_pat])
+              -> @ast::pat {
+    let pat = ast::pat_struct(path, move field_pats, false);
+    mk_pat(cx, span, move pat)
+}
 fn mk_bool(cx: ext_ctxt, span: span, value: bool) -> @ast::expr {
     let lit_expr = ast::expr_lit(@{ node: ast::lit_bool(value), span: span });
     build::mk_expr(cx, span, move lit_expr)
diff --git a/src/libsyntax/ext/deriving.rs b/src/libsyntax/ext/deriving.rs
index 2aca54446d74e..0f8a1a2322756 100644
--- a/src/libsyntax/ext/deriving.rs
+++ b/src/libsyntax/ext/deriving.rs
@@ -318,6 +318,26 @@ fn create_iter_bytes_method(cx: ext_ctxt,
     }
 }
 
+fn create_subpatterns(cx: ext_ctxt,
+                      span: span,
+                      prefix: ~str,
+                      n: uint)
+                   -> ~[@pat] {
+    let subpats = dvec::DVec();
+    for uint::range(0, n) |_i| {
+        // Create the subidentifier.
+        let index = subpats.len().to_str();
+        let ident = cx.ident_of(prefix + index);
+
+        // Create the subpattern.
+        let subpath = build::mk_raw_path(span, ~[ ident ]);
+        let subpat = pat_ident(bind_by_ref(m_imm), subpath, None);
+        let subpat = build::mk_pat(cx, span, move subpat);
+        subpats.push(subpat);
+    }
+    return dvec::unwrap(move subpats);
+}
+
 fn create_enum_variant_pattern(cx: ext_ctxt,
                                span: span,
                                variant: &variant,
@@ -330,25 +350,37 @@ fn create_enum_variant_pattern(cx: ext_ctxt,
                 return build::mk_pat_ident(cx, span, variant_ident);
             }
 
-            let subpats = dvec::DVec();
-            for variant_args.each |_variant_arg| {
-                // Create the subidentifier.
-                let index = subpats.len().to_str();
-                let ident = cx.ident_of(prefix + index);
-
-                // Create the subpattern.
-                let subpath = build::mk_raw_path(span, ~[ ident ]);
-                let subpat = pat_ident(bind_by_ref(m_imm), subpath, None);
-                let subpat = build::mk_pat(cx, span, move subpat);
-                subpats.push(subpat);
-            }
-
             let matching_path = build::mk_raw_path(span, ~[ variant_ident ]);
-            let subpats = dvec::unwrap(move subpats);
+            let subpats = create_subpatterns(cx,
+                                             span,
+                                             prefix,
+                                             variant_args.len());
+
             return build::mk_pat_enum(cx, span, matching_path, move subpats);
         }
-        struct_variant_kind(*) => {
-            cx.span_unimpl(span, ~"struct variants for `deriving`");
+        struct_variant_kind(struct_def) => {
+            let matching_path = build::mk_raw_path(span, ~[ variant_ident ]);
+            let subpats = create_subpatterns(cx,
+                                             span,
+                                             prefix,
+                                             struct_def.fields.len());
+
+            let field_pats = dvec::DVec();
+            for struct_def.fields.eachi |i, struct_field| {
+                let ident = match struct_field.node.kind {
+                    named_field(ident, _, _) => ident,
+                    unnamed_field => {
+                        cx.span_bug(span, ~"unexpected unnamed field");
+                    }
+                };
+                field_pats.push({ ident: ident, pat: subpats[i] });
+            }
+            let field_pats = dvec::unwrap(move field_pats);
+
+            return build::mk_pat_struct(cx,
+                                        span,
+                                        matching_path,
+                                        move field_pats);
         }
         enum_variant_kind(*) => {
             cx.span_unimpl(span, ~"enum variants for `deriving`");
diff --git a/src/test/run-pass/deriving-via-extension-struct-like-enum-variant.rs b/src/test/run-pass/deriving-via-extension-struct-like-enum-variant.rs
new file mode 100644
index 0000000000000..c5e41826a3540
--- /dev/null
+++ b/src/test/run-pass/deriving-via-extension-struct-like-enum-variant.rs
@@ -0,0 +1,12 @@
+#[deriving_eq]
+enum S {
+    X { x: int, y: int },
+    Y
+}
+
+fn main() {
+    let x = X { x: 1, y: 2 };
+    assert x == x;
+    assert !(x != x);
+}
+