Ensure borrows of fn/closure params do not outlive invocations.

resolve_lifetime.rs: Switch from BlockScope to FnScope in ScopeChain
construction. Lifetimes introduced by a fn signature are scoped to the
call-site for that fn. (Note `add_scope_and_walk_fn` must only add
FnScope for the walk of body, *not* of the fn signature.)

region.rs: Introduce new CodeExtentData::CallSiteScope variant. Use
CodeExtentData as the cx.parent, rather than just a NodeId.  Change
DestructionScopeData to CallSiteScopeData.

regionck.rs: Thread call_site_scope via Rcx; constrain fn return
values.

(update; incorporated review feedback from niko.)

Author: pnkfelix

src/librustc/middle/infer/error_reporting.rs

@@ -148,6 +148,9 @@ impl<'tcx> ty::ctxt<'tcx> {
                 };
                 let scope_decorated_tag = match self.region_maps.code_extent_data(scope) {
                     region::CodeExtentData::Misc(_) => tag,
+                    region::CodeExtentData::CallSiteScope { .. } => {
+                        "scope of call-site for function"
+                    }
                     region::CodeExtentData::ParameterScope { .. } => {
                         "scope of parameters for function"
                     }

src/librustc/middle/liveness.rs

@@ -1466,10 +1466,11 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                  entry_ln: LiveNode,
                  body: &hir::Block)
     {
-        // within the fn body, late-bound regions are liberated:
+        // within the fn body, late-bound regions are liberated
+        // and must outlive the *call-site* of the function.
         let fn_ret =
             self.ir.tcx.liberate_late_bound_regions(
-                self.ir.tcx.region_maps.item_extent(body.id),
+                self.ir.tcx.region_maps.call_site_extent(id, body.id),
                 &self.fn_ret(id));
 
         match fn_ret {

src/librustc/middle/region.rs

@@ -125,6 +125,10 @@ pub const DUMMY_CODE_EXTENT : CodeExtent = CodeExtent(1);
 pub enum CodeExtentData {
     Misc(ast::NodeId),
 
+    // extent of the call-site for a function or closure (outlives
+    // the parameters as well as the body).
+    CallSiteScope { fn_id: ast::NodeId, body_id: ast::NodeId },
+
     // extent of parameters passed to a function or closure (they
     // outlive its body)
     ParameterScope { fn_id: ast::NodeId, body_id: ast::NodeId },
@@ -136,20 +140,20 @@ pub enum CodeExtentData {
     Remainder(BlockRemainder)
 }
 
-/// extent of destructors for temporaries of node-id
+/// extent of call-site for a function/method.
 #[derive(Clone, PartialEq, PartialOrd, Eq, Ord, Hash, RustcEncodable,
            RustcDecodable, Debug, Copy)]
-pub struct DestructionScopeData {
-    pub node_id: ast::NodeId
+pub struct CallSiteScopeData {
+    pub fn_id: ast::NodeId, pub body_id: ast::NodeId,
 }
 
-impl DestructionScopeData {
-    pub fn new(node_id: ast::NodeId) -> DestructionScopeData {
-        DestructionScopeData { node_id: node_id }
-    }
+impl CallSiteScopeData {
     pub fn to_code_extent(&self, region_maps: &RegionMaps) -> CodeExtent {
         region_maps.lookup_code_extent(
-            CodeExtentData::DestructionScope(self.node_id))
+            match *self {
+                CallSiteScopeData { fn_id, body_id } =>
+                    CodeExtentData::CallSiteScope { fn_id: fn_id, body_id: body_id },
+            })
     }
 }
 
@@ -190,6 +194,7 @@ impl CodeExtentData {
             // precise extent denoted by `self`.
             CodeExtentData::Remainder(br) => br.block,
             CodeExtentData::DestructionScope(node_id) => node_id,
+            CodeExtentData::CallSiteScope { fn_id: _, body_id } |
             CodeExtentData::ParameterScope { fn_id: _, body_id } => body_id,
         }
     }
@@ -215,6 +220,7 @@ impl CodeExtent {
         match ast_map.find(self.node_id(region_maps)) {
             Some(ast_map::NodeBlock(ref blk)) => {
                 match region_maps.code_extent_data(*self) {
+                    CodeExtentData::CallSiteScope { .. } |
                     CodeExtentData::ParameterScope { .. } |
                     CodeExtentData::Misc(_) |
                     CodeExtentData::DestructionScope(_) => Some(blk.span),
@@ -346,6 +352,10 @@ impl RegionMaps {
     pub fn item_extent(&self, n: ast::NodeId) -> CodeExtent {
         self.lookup_code_extent(CodeExtentData::DestructionScope(n))
     }
+    pub fn call_site_extent(&self, fn_id: ast::NodeId, body_id: ast::NodeId) -> CodeExtent {
+        assert!(fn_id != body_id);
+        self.lookup_code_extent(CodeExtentData::CallSiteScope { fn_id: fn_id, body_id: body_id })
+    }
     pub fn opt_destruction_extent(&self, n: ast::NodeId) -> Option<CodeExtent> {
         self.code_extent_interner.borrow().get(&CodeExtentData::DestructionScope(n)).cloned()
     }
@@ -1101,6 +1111,9 @@ fn resolve_fn(visitor: &mut RegionResolutionVisitor,
            body.id,
            visitor.cx.parent);
 
+    visitor.cx.parent = visitor.new_code_extent(
+        CodeExtentData::CallSiteScope { fn_id: id, body_id: body.id });
+
     let fn_decl_scope = visitor.new_code_extent(
         CodeExtentData::ParameterScope { fn_id: id, body_id: body.id });
 

src/librustc/middle/resolve_lifetime.rs

@@ -42,7 +42,7 @@ pub enum DefRegion {
                         /* lifetime decl */ ast::NodeId),
     DefLateBoundRegion(ty::DebruijnIndex,
                        /* lifetime decl */ ast::NodeId),
-    DefFreeRegion(/* block scope */ region::DestructionScopeData,
+    DefFreeRegion(region::CallSiteScopeData,
                   /* lifetime decl */ ast::NodeId),
 }
 
@@ -83,9 +83,9 @@ enum ScopeChain<'a> {
     /// LateScope(['a, 'b, ...], s) extends s with late-bound
     /// lifetimes introduced by the declaration binder_id.
     LateScope(&'a Vec<hir::LifetimeDef>, Scope<'a>),
-    /// lifetimes introduced by items within a code block are scoped
-    /// to that block.
-    BlockScope(region::DestructionScopeData, Scope<'a>),
+
+    /// lifetimes introduced by a fn are scoped to the call-site for that fn.
+    FnScope { fn_id: ast::NodeId, body_id: ast::NodeId, s: Scope<'a> },
     RootScope
 }
 
@@ -172,20 +172,20 @@ impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
     }
 
     fn visit_fn(&mut self, fk: FnKind<'v>, fd: &'v hir::FnDecl,
-                b: &'v hir::Block, s: Span, _: ast::NodeId) {
+                b: &'v hir::Block, s: Span, fn_id: ast::NodeId) {
         match fk {
             FnKind::ItemFn(_, generics, _, _, _, _) => {
                 self.visit_early_late(subst::FnSpace, generics, |this| {
-                    this.walk_fn(fk, fd, b, s)
+                    this.add_scope_and_walk_fn(fk, fd, b, s, fn_id)
                 })
             }
             FnKind::Method(_, sig, _) => {
                 self.visit_early_late(subst::FnSpace, &sig.generics, |this| {
-                    this.walk_fn(fk, fd, b, s)
+                    this.add_scope_and_walk_fn(fk, fd, b, s, fn_id)
                 })
             }
             FnKind::Closure => {
-                self.walk_fn(fk, fd, b, s)
+                self.add_scope_and_walk_fn(fk, fd, b, s, fn_id)
             }
         }
     }
@@ -236,12 +236,6 @@ impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
         replace(&mut self.labels_in_fn, saved);
     }
 
-    fn visit_block(&mut self, b: &hir::Block) {
-        self.with(BlockScope(region::DestructionScopeData::new(b.id),
-                             self.scope),
-                  |_, this| intravisit::walk_block(this, b));
-    }
-
     fn visit_lifetime(&mut self, lifetime_ref: &hir::Lifetime) {
         if lifetime_ref.name == special_idents::static_lifetime.name {
             self.insert_lifetime(lifetime_ref, DefStaticRegion);
@@ -437,7 +431,7 @@ fn extract_labels<'v, 'a>(ctxt: &mut LifetimeContext<'a>, b: &'v hir::Block) {
                                            label_span: Span) {
         loop {
             match *scope {
-                BlockScope(_, s) => { scope = s; }
+                FnScope { s, .. } => { scope = s; }
                 RootScope => { return; }
 
                 EarlyScope(_, lifetimes, s) |
@@ -461,14 +455,13 @@ fn extract_labels<'v, 'a>(ctxt: &mut LifetimeContext<'a>, b: &'v hir::Block) {
 }
 
 impl<'a> LifetimeContext<'a> {
-    // This is just like intravisit::walk_fn, except that it extracts the
-    // labels of the function body and swaps them in before visiting
-    // the function body itself.
-    fn walk_fn<'b>(&mut self,
-                   fk: FnKind,
-                   fd: &hir::FnDecl,
-                   fb: &'b hir::Block,
-                   _span: Span) {
+    fn add_scope_and_walk_fn<'b>(&mut self,
+                                 fk: FnKind,
+                                 fd: &hir::FnDecl,
+                                 fb: &'b hir::Block,
+                                 _span: Span,
+                                 fn_id: ast::NodeId) {
+
         match fk {
             FnKind::ItemFn(_, generics, _, _, _, _) => {
                 intravisit::walk_fn_decl(self, fd);
@@ -488,7 +481,8 @@ impl<'a> LifetimeContext<'a> {
         // `self.labels_in_fn`.
         extract_labels(self, fb);
 
-        self.visit_block(fb);
+        self.with(FnScope { fn_id: fn_id, body_id: fb.id, s: self.scope },
+                  |_old_scope, this| this.visit_block(fb))
     }
 
     fn with<F>(&mut self, wrap_scope: ScopeChain, f: F) where
@@ -559,8 +553,11 @@ impl<'a> LifetimeContext<'a> {
         let mut scope = self.scope;
         loop {
             match *scope {
-                BlockScope(blk_scope, s) => {
-                    return self.resolve_free_lifetime_ref(blk_scope, lifetime_ref, s);
+                FnScope {fn_id, body_id, s } => {
+                    return self.resolve_free_lifetime_ref(
+                        region::CallSiteScopeData { fn_id: fn_id, body_id: body_id },
+                        lifetime_ref,
+                        s);
                 }
 
                 RootScope => {
@@ -604,7 +601,7 @@ impl<'a> LifetimeContext<'a> {
     }
 
     fn resolve_free_lifetime_ref(&mut self,
-                                 scope_data: region::DestructionScopeData,
+                                 scope_data: region::CallSiteScopeData,
                                  lifetime_ref: &hir::Lifetime,
                                  scope: Scope) {
         debug!("resolve_free_lifetime_ref \
@@ -622,8 +619,10 @@ impl<'a> LifetimeContext<'a> {
                     scope_data: {:?} scope: {:?} search_result: {:?}",
                    scope_data, scope, search_result);
             match *scope {
-                BlockScope(blk_scope_data, s) => {
-                    scope_data = blk_scope_data;
+                FnScope { fn_id, body_id, s } => {
+                    scope_data = region::CallSiteScopeData {
+                        fn_id: fn_id, body_id: body_id
+                    };
                     scope = s;
                 }
 
@@ -711,7 +710,7 @@ impl<'a> LifetimeContext<'a> {
 
         loop {
             match *old_scope {
-                BlockScope(_, s) => {
+                FnScope { s, .. } => {
                     old_scope = s;
                 }
 
@@ -864,7 +863,7 @@ impl<'a> fmt::Debug for ScopeChain<'a> {
         match *self {
             EarlyScope(space, defs, _) => write!(fmt, "EarlyScope({:?}, {:?})", space, defs),
             LateScope(defs, _) => write!(fmt, "LateScope({:?})", defs),
-            BlockScope(id, _) => write!(fmt, "BlockScope({:?})", id),
+            FnScope { fn_id, body_id, s: _ } => write!(fmt, "FnScope({:?}, {:?})", fn_id, body_id),
             RootScope => write!(fmt, "RootScope"),
         }
     }

src/librustc/middle/traits/object_safety.rs

@@ -192,7 +192,8 @@ fn generics_require_sized_self<'tcx>(tcx: &ty::ctxt<'tcx>,
     };
 
     // Search for a predicate like `Self : Sized` amongst the trait bounds.
-    let free_substs = tcx.construct_free_substs(generics, ast::DUMMY_NODE_ID);
+    let free_substs = tcx.construct_free_substs(generics,
+                                                tcx.region_maps.node_extent(ast::DUMMY_NODE_ID));
     let predicates = predicates.instantiate(tcx, &free_substs).predicates.into_vec();
     elaborate_predicates(tcx, predicates)
         .any(|predicate| {