Fix range literals borrowing suggestions

src/librustc_typeck/check/demand.rs

@@ -309,11 +309,16 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 };
                 if self.can_coerce(ref_ty, expected) {
                     if let Ok(src) = cm.span_to_snippet(sp) {
-                        let sugg_expr = match expr.node { // parenthesize if needed (Issue #46756)
+                        let needs_parens = match expr.node {
+                            // parenthesize if needed (Issue #46756)
                             hir::ExprKind::Cast(_, _) |
-                            hir::ExprKind::Binary(_, _, _) => format!("({})", src),
-                            _ => src,
+                            hir::ExprKind::Binary(_, _, _) => true,
+                            // parenthesize borrows of range literals (Issue #54505)
+                            _ if self.is_range_literal(expr) => true,
+                            _ => false,
                         };
+                        let sugg_expr = if needs_parens { format!("({})", src) } else { src };
+
                         if let Some(sugg) = self.can_use_as_ref(expr) {
                             return Some(sugg);
                         }
@@ -374,6 +379,77 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         None
     }
 
+    // This function checks if the specified expression is a built-in range literal
+    // (See: librustc/hir/lowering.rs::LoweringContext::lower_expr() )
+    fn is_range_literal(&self, expr: &hir::Expr) -> bool {
+        use hir::{Path, QPath, ExprKind, TyKind};
+
+        // we support `::std::ops::Range` and `::std::core::Range` prefixes
+        // (via split on "|")
+        let ops_path = ["{{root}}", "std|core", "ops"];
+
+        let is_range_path = |path: &Path| {
+            let ident_names: Vec<_> = path.segments
+                .iter()
+                .map(|seg| seg.ident.as_str())
+                .collect();
+
+            if let Some((last, preceding)) = ident_names.split_last() {
+                last.starts_with("Range") &&
+                    preceding.len() == 3 &&
+                    preceding.iter()
+                        .zip(ops_path.iter())
+                        .all(|(seg, match_seg)| {
+                            match_seg.split("|")
+                                .into_iter()
+                                .any(|ref spl_seg| seg == spl_seg)
+                        })
+            } else {
+                false
+            }
+        };
+
+        let is_range_struct_snippet = |span: &Span| {
+            // Tell if expression span snippet looks like an explicit
+            // Range struct or new() call.  This is to allow rejecting
+            // Ranges constructed with non-literals.
+            let source_map = self.tcx.sess.source_map();
+            let end_point = source_map.end_point(*span);
+
+            if let Ok(end_string) = source_map.span_to_snippet(end_point) {
+                end_string.ends_with("}") || end_string.ends_with(")")
+            } else {
+                false
+            }
+
+        };
+
+        match expr.node {
+            // all built-in range literals but `..=` and `..`
+            // desugar to Structs, `..` desugars to its struct path
+            ExprKind::Struct(QPath::Resolved(None, ref path), _, _) |
+            ExprKind::Path(QPath::Resolved(None, ref path)) => {
+                return is_range_path(&path) && !is_range_struct_snippet(&expr.span);
+            }
+
+            // `..=` desugars into RangeInclusive::new(...)
+            ExprKind::Call(ref func, _) => {
+                if let ExprKind::Path(QPath::TypeRelative(ref ty, ref segment)) = func.node {
+                    if let TyKind::Path(QPath::Resolved(None, ref path)) = ty.node {
+                        let calls_new = segment.ident.as_str() == "new";
+
+                        return is_range_path(&path) && calls_new &&
+                            !is_range_struct_snippet(&expr.span);
+                    }
+                }
+            }
+
+            _ => {}
+        }
+
+        false
+    }
+
     pub fn check_for_cast(&self,
                       err: &mut DiagnosticBuilder<'tcx>,
                       expr: &hir::Expr,

src/test/ui/range/issue-54505-no-literals.fixed

@@ -0,0 +1,85 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// run-rustfix
+
+// Regression test for changes introduced while fixing #54505
+
+// This test uses non-literals for Ranges
+// (expecting no parens with borrow suggestion)
+
+use std::ops::RangeBounds;
+
+
+// take a reference to any built-in range
+fn take_range(_r: &impl RangeBounds<i8>) {}
+
+
+fn main() {
+    take_range(&std::ops::Range { start: 0, end: 1 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &std::ops::Range { start: 0, end: 1 }
+
+    take_range(&::std::ops::Range { start: 0, end: 1 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &::std::ops::Range { start: 0, end: 1 }
+
+    take_range(&std::ops::RangeFrom { start: 1 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &std::ops::RangeFrom { start: 1 }
+
+    take_range(&::std::ops::RangeFrom { start: 1 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &::std::ops::RangeFrom { start: 1 }
+
+    take_range(&std::ops::RangeFull {});
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &std::ops::RangeFull {}
+
+    take_range(&::std::ops::RangeFull {});
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &::std::ops::RangeFull {}
+
+    take_range(&std::ops::RangeInclusive::new(0, 1));
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &std::ops::RangeInclusive::new(0, 1)
+
+    take_range(&::std::ops::RangeInclusive::new(0, 1));
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &::std::ops::RangeInclusive::new(0, 1)
+
+    take_range(&std::ops::RangeTo { end: 5 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &std::ops::RangeTo { end: 5 }
+
+    take_range(&::std::ops::RangeTo { end: 5 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &::std::ops::RangeTo { end: 5 }
+
+    take_range(&std::ops::RangeToInclusive { end: 5 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &std::ops::RangeToInclusive { end: 5 }
+
+    take_range(&::std::ops::RangeToInclusive { end: 5 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &::std::ops::RangeToInclusive { end: 5 }
+}

src/test/ui/range/issue-54505-no-literals.rs

@@ -0,0 +1,85 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// run-rustfix
+
+// Regression test for changes introduced while fixing #54505
+
+// This test uses non-literals for Ranges
+// (expecting no parens with borrow suggestion)
+
+use std::ops::RangeBounds;
+
+
+// take a reference to any built-in range
+fn take_range(_r: &impl RangeBounds<i8>) {}
+
+
+fn main() {
+    take_range(std::ops::Range { start: 0, end: 1 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &std::ops::Range { start: 0, end: 1 }
+
+    take_range(::std::ops::Range { start: 0, end: 1 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &::std::ops::Range { start: 0, end: 1 }
+
+    take_range(std::ops::RangeFrom { start: 1 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &std::ops::RangeFrom { start: 1 }
+
+    take_range(::std::ops::RangeFrom { start: 1 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &::std::ops::RangeFrom { start: 1 }
+
+    take_range(std::ops::RangeFull {});
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &std::ops::RangeFull {}
+
+    take_range(::std::ops::RangeFull {});
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &::std::ops::RangeFull {}
+
+    take_range(std::ops::RangeInclusive::new(0, 1));
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &std::ops::RangeInclusive::new(0, 1)
+
+    take_range(::std::ops::RangeInclusive::new(0, 1));
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &::std::ops::RangeInclusive::new(0, 1)
+
+    take_range(std::ops::RangeTo { end: 5 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &std::ops::RangeTo { end: 5 }
+
+    take_range(::std::ops::RangeTo { end: 5 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &::std::ops::RangeTo { end: 5 }
+
+    take_range(std::ops::RangeToInclusive { end: 5 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &std::ops::RangeToInclusive { end: 5 }
+
+    take_range(::std::ops::RangeToInclusive { end: 5 });
+    //~^ ERROR mismatched types [E0308]
+    //~| HELP consider borrowing here
+    //~| SUGGESTION &::std::ops::RangeToInclusive { end: 5 }
+}