Add support for patterns referencing non-trivial statics

This is accomplished by rewriting static expressions into equivalent patterns.
This way, patterns referencing static variables can both participate
in exhaustiveness analysis as well as be compiled down into the appropriate
branch of the decision trees that match expressions are codegened to.

Fixes #6533.
Fixes #13626.
Fixes #13731.
Fixes #14576.
Fixes #15393.

Author: Jakub Wieczorek

src/librustc/lib.rs

@@ -68,42 +68,42 @@ pub mod back {
 }
 
 pub mod middle {
-    pub mod def;
-    pub mod trans;
-    pub mod ty;
-    pub mod ty_fold;
-    pub mod subst;
-    pub mod resolve;
-    pub mod resolve_lifetime;
-    pub mod typeck;
+    pub mod astencode;
+    pub mod borrowck;
+    pub mod cfg;
+    pub mod check_const;
     pub mod check_loop;
     pub mod check_match;
-    pub mod check_const;
     pub mod check_static;
-    pub mod borrowck;
+    pub mod const_eval;
     pub mod dataflow;
-    pub mod mem_categorization;
-    pub mod liveness;
-    pub mod kind;
+    pub mod dead;
+    pub mod def;
+    pub mod dependency_format;
+    pub mod effect;
+    pub mod entry;
+    pub mod expr_use_visitor;
     pub mod freevars;
-    pub mod pat_util;
-    pub mod region;
-    pub mod const_eval;
-    pub mod astencode;
+    pub mod graph;
+    pub mod intrinsicck;
+    pub mod kind;
     pub mod lang_items;
+    pub mod liveness;
+    pub mod mem_categorization;
+    pub mod pat_util;
     pub mod privacy;
-    pub mod entry;
-    pub mod effect;
     pub mod reachable;
-    pub mod graph;
-    pub mod cfg;
-    pub mod dead;
-    pub mod expr_use_visitor;
-    pub mod dependency_format;
-    pub mod weak_lang_items;
+    pub mod region;
+    pub mod resolve;
+    pub mod resolve_lifetime;
     pub mod save;
-    pub mod intrinsicck;
     pub mod stability;
+    pub mod subst;
+    pub mod trans;
+    pub mod ty;
+    pub mod ty_fold;
+    pub mod typeck;
+    pub mod weak_lang_items;
 }
 
 pub mod front {

src/librustc/middle/check_match.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 use middle::const_eval::{compare_const_vals, const_bool, const_float, const_nil, const_val};
-use middle::const_eval::{eval_const_expr, lookup_const_by_id};
+use middle::const_eval::{const_expr_to_pat, eval_const_expr, lookup_const_by_id};
 use middle::def::*;
 use middle::pat_util::*;
 use middle::ty::*;
@@ -21,8 +21,9 @@ use std::iter::range_inclusive;
 use syntax::ast::*;
 use syntax::ast_util::{is_unguarded, walk_pat};
 use syntax::codemap::{Span, Spanned, DUMMY_SP};
-use syntax::owned_slice::OwnedSlice;
+use syntax::fold::{Folder, noop_fold_pat};
 use syntax::print::pprust::pat_to_string;
+use syntax::parse::token;
 use syntax::visit;
 use syntax::visit::{Visitor, FnKind};
 use util::ppaux::ty_to_string;
@@ -76,6 +77,12 @@ impl fmt::Show for Matrix {
     }
 }
 
+impl FromIterator<Vec<Gc<Pat>>> for Matrix {
+    fn from_iter<T: Iterator<Vec<Gc<Pat>>>>(mut iterator: T) -> Matrix {
+        Matrix(iterator.collect())
+    }
+}
+
 pub struct MatchCheckCtxt<'a> {
     pub tcx: &'a ty::ctxt
 }
@@ -120,10 +127,8 @@ impl<'a> Visitor<()> for MatchCheckCtxt<'a> {
 }
 
 pub fn check_crate(tcx: &ty::ctxt, krate: &Crate) {
-    let mut cx = MatchCheckCtxt { tcx: tcx, };
-
+    let mut cx = MatchCheckCtxt { tcx: tcx };
     visit::walk_crate(&mut cx, krate, ());
-
     tcx.sess.abort_if_errors();
 }
 
@@ -155,48 +160,49 @@ fn check_expr(cx: &mut MatchCheckCtxt, ex: &Expr) {
                 // If the type *is* empty, it's vacuously exhaustive
                 return;
             }
-            let m: Matrix = Matrix(arms
+
+            let mut static_inliner = StaticInliner { tcx: cx.tcx };
+            let matrix: Matrix = arms
                 .iter()
                 .filter(|&arm| is_unguarded(arm))
                 .flat_map(|arm| arm.pats.iter())
-                .map(|pat| vec!(pat.clone()))
-                .collect());
-            check_exhaustive(cx, ex.span, &m);
+                .map(|pat| vec![static_inliner.fold_pat(*pat)])
+                .collect();
+            check_exhaustive(cx, ex.span, &matrix);
         },
         _ => ()
     }
 }
 
+fn is_expr_const_nan(tcx: &ty::ctxt, expr: &Expr) -> bool {
+    match eval_const_expr(tcx, expr) {
+        const_float(f) => f.is_nan(),
+        _ => false
+    }
+}
+
 // Check for unreachable patterns
 fn check_arms(cx: &MatchCheckCtxt, arms: &[Arm]) {
     let mut seen = Matrix(vec!());
+    let mut static_inliner = StaticInliner { tcx: cx.tcx };
     for arm in arms.iter() {
         for pat in arm.pats.iter() {
+            let inlined = static_inliner.fold_pat(*pat);
+
             // Check that we do not match against a static NaN (#6804)
-            let pat_matches_nan: |&Pat| -> bool = |p| {
-                let opt_def = cx.tcx.def_map.borrow().find_copy(&p.id);
-                match opt_def {
-                    Some(DefStatic(did, false)) => {
-                        let const_expr = lookup_const_by_id(cx.tcx, did).unwrap();
-                        match eval_const_expr(cx.tcx, &*const_expr) {
-                            const_float(f) if f.is_nan() => true,
-                            _ => false
-                        }
+            walk_pat(&*inlined, |p| {
+                match p.node {
+                    PatLit(expr) if is_expr_const_nan(cx.tcx, &*expr) => {
+                        span_warn!(cx.tcx.sess, pat.span, E0003,
+                            "unmatchable NaN in pattern, \
+                             use the is_nan method in a guard instead");
                     }
-                    _ => false
-                }
-            };
-
-            walk_pat(&**pat, |p| {
-                if pat_matches_nan(p) {
-                    span_warn!(cx.tcx.sess, p.span, E0003,
-                        "unmatchable NaN in pattern, use the is_nan method in a guard instead"
-                    );
+                    _ => ()
                 }
                 true
             });
 
-            let v = vec!(*pat);
+            let v = vec![inlined];
             match is_useful(cx, &seen, v.as_slice(), LeaveOutWitness) {
                 NotUseful => span_err!(cx.tcx.sess, pat.span, E0001, "unreachable pattern"),
                 Useful => (),
@@ -218,8 +224,8 @@ fn raw_pat(p: Gc<Pat>) -> Gc<Pat> {
     }
 }
 
-fn check_exhaustive(cx: &MatchCheckCtxt, sp: Span, m: &Matrix) {
-    match is_useful(cx, m, [wild()], ConstructWitness) {
+fn check_exhaustive(cx: &MatchCheckCtxt, sp: Span, matrix: &Matrix) {
+    match is_useful(cx, matrix, [wild()], ConstructWitness) {
         UsefulWithWitness(pats) => {
             let witness = match pats.as_slice() {
                 [witness] => witness,
@@ -251,16 +257,26 @@ fn const_val_to_expr(value: &const_val) -> Gc<Expr> {
     }
 }
 
-fn def_to_path(tcx: &ty::ctxt, id: DefId) -> Path {
-    ty::with_path(tcx, id, |mut path| Path {
-        global: false,
-        segments: path.last().map(|elem| PathSegment {
-            identifier: Ident::new(elem.name()),
-            lifetimes: vec!(),
-            types: OwnedSlice::empty()
-        }).move_iter().collect(),
-        span: DUMMY_SP,
-    })
+pub struct StaticInliner<'a> {
+    pub tcx: &'a ty::ctxt
+}
+
+impl<'a> Folder for StaticInliner<'a> {
+    fn fold_pat(&mut self, pat: Gc<Pat>) -> Gc<Pat> {
+        match pat.node {
+            PatIdent(..) | PatEnum(..) => {
+                let def = self.tcx.def_map.borrow().find_copy(&pat.id);
+                match def {
+                    Some(DefStatic(did, _)) => {
+                        let const_expr = lookup_const_by_id(self.tcx, did).unwrap();
+                        const_expr_to_pat(self.tcx, const_expr)
+                    },
+                    _ => noop_fold_pat(pat, self)
+                }
+            }
+            _ => noop_fold_pat(pat, self)
+        }
+    }
 }
 
 /// Constructs a partial witness for a pattern given a list of
@@ -283,9 +299,11 @@ fn construct_witness(cx: &MatchCheckCtxt, ctor: &Constructor,
 
         ty::ty_enum(cid, _) | ty::ty_struct(cid, _)  => {
             let (vid, is_structure) = match ctor {
-                &Variant(vid) => (vid,
-                    ty::enum_variant_with_id(cx.tcx, cid, vid).arg_names.is_some()),
-                _ => (cid, true)
+                &Variant(vid) =>
+                    (vid, ty::enum_variant_with_id(cx.tcx, cid, vid).arg_names.is_some()),
+                _ =>
+                    (cid, ty::lookup_struct_fields(cx.tcx, cid).iter()
+                        .any(|field| field.name != token::special_idents::unnamed_field.name))
             };
             if is_structure {
                 let fields = ty::lookup_struct_fields(cx.tcx, vid);
@@ -459,8 +477,7 @@ fn is_useful(cx: &MatchCheckCtxt, matrix @ &Matrix(ref rows): &Matrix,
             },
 
             Some(constructor) => {
-                let matrix = Matrix(rows.iter().filter_map(|r|
-                    default(cx, r.as_slice())).collect());
+                let matrix = rows.iter().filter_map(|r| default(cx, r.as_slice())).collect();
                 match is_useful(cx, &matrix, v.tail(), witness) {
                     UsefulWithWitness(pats) => {
                         let arity = constructor_arity(cx, &constructor, left_ty);
@@ -506,25 +523,23 @@ fn pat_constructors(cx: &MatchCheckCtxt, p: Gc<Pat>,
     match pat.node {
         PatIdent(..) =>
             match cx.tcx.def_map.borrow().find(&pat.id) {
-                Some(&DefStatic(did, false)) => {
-                    let const_expr = lookup_const_by_id(cx.tcx, did).unwrap();
-                    vec!(ConstantValue(eval_const_expr(cx.tcx, &*const_expr)))
-                },
+                Some(&DefStatic(..)) =>
+                    cx.tcx.sess.span_bug(pat.span, "static pattern should've been rewritten"),
                 Some(&DefStruct(_)) => vec!(Single),
                 Some(&DefVariant(_, id, _)) => vec!(Variant(id)),
                 _ => vec!()
             },
         PatEnum(..) =>
             match cx.tcx.def_map.borrow().find(&pat.id) {
-                Some(&DefStatic(did, false)) => {
-                    let const_expr = lookup_const_by_id(cx.tcx, did).unwrap();
-                    vec!(ConstantValue(eval_const_expr(cx.tcx, &*const_expr)))
-                },
+                Some(&DefStatic(..)) =>
+                    cx.tcx.sess.span_bug(pat.span, "static pattern should've been rewritten"),
                 Some(&DefVariant(_, id, _)) => vec!(Variant(id)),
                 _ => vec!(Single)
             },
         PatStruct(..) =>
             match cx.tcx.def_map.borrow().find(&pat.id) {
+                Some(&DefStatic(..)) =>
+                    cx.tcx.sess.span_bug(pat.span, "static pattern should've been rewritten"),
                 Some(&DefVariant(_, id, _)) => vec!(Variant(id)),
                 _ => vec!(Single)
             },
@@ -583,7 +598,7 @@ pub fn constructor_arity(cx: &MatchCheckCtxt, ctor: &Constructor, ty: ty::t) ->
 }
 
 fn range_covered_by_constructor(ctor: &Constructor,
-                                from: &const_val,to: &const_val) -> Option<bool> {
+                                from: &const_val, to: &const_val) -> Option<bool> {
     let (c_from, c_to) = match *ctor {
         ConstantValue(ref value)        => (value, value),
         ConstantRange(ref from, ref to) => (from, to),
@@ -621,44 +636,22 @@ pub fn specialize(cx: &MatchCheckCtxt, r: &[Gc<Pat>],
         &PatIdent(_, _, _) => {
             let opt_def = cx.tcx.def_map.borrow().find_copy(&pat_id);
             match opt_def {
+                Some(DefStatic(..)) =>
+                    cx.tcx.sess.span_bug(pat_span, "static pattern should've been rewritten"),
                 Some(DefVariant(_, id, _)) => if *constructor == Variant(id) {
                     Some(vec!())
                 } else {
                     None
                 },
-                Some(DefStatic(did, _)) => {
-                    let const_expr = lookup_const_by_id(cx.tcx, did).unwrap();
-                    let e_v = eval_const_expr(cx.tcx, &*const_expr);
-                    match range_covered_by_constructor(constructor, &e_v, &e_v) {
-                        Some(true) => Some(vec!()),
-                        Some(false) => None,
-                        None => {
-                            cx.tcx.sess.span_err(pat_span, "mismatched types between arms");
-                            None
-                        }
-                    }
-                }
-                _ => {
-                    Some(Vec::from_elem(arity, wild()))
-                }
+                _ => Some(Vec::from_elem(arity, wild()))
             }
         }
 
         &PatEnum(_, ref args) => {
             let def = cx.tcx.def_map.borrow().get_copy(&pat_id);
             match def {
-                DefStatic(did, _) => {
-                    let const_expr = lookup_const_by_id(cx.tcx, did).unwrap();
-                    let e_v = eval_const_expr(cx.tcx, &*const_expr);
-                    match range_covered_by_constructor(constructor, &e_v, &e_v) {
-                        Some(true) => Some(vec!()),
-                        Some(false) => None,
-                        None => {
-                            cx.tcx.sess.span_err(pat_span, "mismatched types between arms");
-                            None
-                        }
-                    }
-                }
+                DefStatic(..) =>
+                    cx.tcx.sess.span_bug(pat_span, "static pattern should've been rewritten"),
                 DefVariant(_, id, _) if *constructor != Variant(id) => None,
                 DefVariant(..) | DefFn(..) | DefStruct(..) => {
                     Some(match args {
@@ -674,6 +667,8 @@ pub fn specialize(cx: &MatchCheckCtxt, r: &[Gc<Pat>],
             // Is this a struct or an enum variant?
             let def = cx.tcx.def_map.borrow().get_copy(&pat_id);
             let class_id = match def {
+                DefStatic(..) =>
+                    cx.tcx.sess.span_bug(pat_span, "static pattern should've been rewritten"),
                 DefVariant(_, variant_id, _) => if *constructor == Variant(variant_id) {
                     Some(variant_id)
                 } else {
@@ -782,7 +777,8 @@ fn check_local(cx: &mut MatchCheckCtxt, loc: &Local) {
         LocalFor => "`for` loop"
     };
 
-    match is_refutable(cx, loc.pat) {
+    let mut static_inliner = StaticInliner { tcx: cx.tcx };
+    match is_refutable(cx, static_inliner.fold_pat(loc.pat)) {
         Some(pat) => {
             span_err!(cx.tcx.sess, loc.pat.span, E0005,
                 "refutable pattern in {} binding: `{}` not covered",