Rollup of 6 pull requests

src/bootstrap/test.rs

@@ -154,6 +154,7 @@ impl Step for Cargotest {
     fn run(self, builder: &Builder<'_>) {
         let compiler = builder.compiler(self.stage, self.host);
         builder.ensure(compile::Rustc { compiler, target: compiler.host });
+        let cargo = builder.ensure(tool::Cargo { compiler, target: compiler.host });
 
         // Note that this is a short, cryptic, and not scoped directory name. This
         // is currently to minimize the length of path on Windows where we otherwise
@@ -165,7 +166,7 @@ impl Step for Cargotest {
         let mut cmd = builder.tool_cmd(Tool::CargoTest);
         try_run(
             builder,
-            cmd.arg(&builder.initial_cargo)
+            cmd.arg(&cargo)
                 .arg(&out_dir)
                 .env("RUSTC", builder.rustc(compiler))
                 .env("RUSTDOC", builder.rustdoc(compiler)),

src/librustc_ast/ast.rs

@@ -25,6 +25,7 @@ pub use UnsafeSource::*;
 use crate::ptr::P;
 use crate::token::{self, DelimToken};
 use crate::tokenstream::{DelimSpan, TokenStream, TokenTree};
+use crate::visit::{walk_ty, Visitor};
 
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::Lrc;
@@ -1795,6 +1796,26 @@ pub struct Ty {
     pub span: Span,
 }
 
+impl Ty {
+    /// Returns `true` if the kind of this type or any types contained within are `impl Trait`.
+    pub fn contains_impl_trait(&self) -> bool {
+        struct ContainsImplTrait(bool);
+
+        impl<'ast> Visitor<'ast> for ContainsImplTrait {
+            fn visit_ty(&mut self, t: &'ast Ty) {
+                self.0 |= matches!(t.kind, TyKind::ImplTrait(..));
+                if !self.0 {
+                    walk_ty(self, t);
+                }
+            }
+        }
+
+        let mut vis = ContainsImplTrait(false);
+        vis.visit_ty(self);
+        vis.0
+    }
+}
+
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub struct BareFnTy {
     pub unsafety: Unsafe,

src/librustc_error_codes/error_codes.rs

@@ -439,6 +439,7 @@ E0752: include_str!("./error_codes/E0752.md"),
 E0753: include_str!("./error_codes/E0753.md"),
 E0754: include_str!("./error_codes/E0754.md"),
 E0758: include_str!("./error_codes/E0758.md"),
+E0759: include_str!("./error_codes/E0759.md"),
 E0760: include_str!("./error_codes/E0760.md"),
 E0761: include_str!("./error_codes/E0761.md"),
 E0762: include_str!("./error_codes/E0762.md"),

src/librustc_error_codes/error_codes/E0759.md

@@ -0,0 +1,67 @@
+A `'static` requirement in a return type involving a trait is not fulfilled.
+
+Erroneous code examples:
+
+```compile_fail,E0759
+use std::fmt::Debug;
+
+fn foo(x: &i32) -> impl Debug {
+    x
+}
+```
+
+```compile_fail,E0759
+# use std::fmt::Debug;
+fn bar(x: &i32) -> Box<dyn Debug> {
+    Box::new(x)
+}
+```
+
+These examples have the same semantics as the following:
+
+```compile_fail,E0759
+# use std::fmt::Debug;
+fn foo(x: &i32) -> impl Debug + 'static {
+    x
+}
+```
+
+```compile_fail,E0759
+# use std::fmt::Debug;
+fn bar(x: &i32) -> Box<dyn Debug + 'static> {
+    Box::new(x)
+}
+```
+
+Both [`dyn Trait`] and [`impl Trait`] in return types have a an implicit
+`'static` requirement, meaning that the value implementing them that is being
+returned has to be either a `'static` borrow or an owned value.
+
+In order to change the requirement from `'static` to be a lifetime derived from
+its arguments, you can add an explicit bound, either to an anonymous lifetime
+`'_` or some appropriate named lifetime.
+
+```
+# use std::fmt::Debug;
+fn foo(x: &i32) -> impl Debug + '_ {
+    x
+}
+fn bar(x: &i32) -> Box<dyn Debug + '_> {
+    Box::new(x)
+}
+```
+
+These are equivalent to the following explicit lifetime annotations:
+
+```
+# use std::fmt::Debug;
+fn foo<'a>(x: &'a i32) -> impl Debug + 'a {
+    x
+}
+fn bar<'a>(x: &'a i32) -> Box<dyn Debug + 'a> {
+    Box::new(x)
+}
+```
+
+[`dyn Trait`]: https://doc.rust-lang.org/book/ch17-02-trait-objects.html#using-trait-objects-that-allow-for-values-of-different-types
+[`impl Trait`]: https://doc.rust-lang.org/book/ch10-02-traits.html#returning-types-that-implement-traits

src/librustc_errors/diagnostic.rs

@@ -296,6 +296,29 @@ impl Diagnostic {
         self
     }
 
+    pub fn multipart_suggestions(
+        &mut self,
+        msg: &str,
+        suggestions: Vec<Vec<(Span, String)>>,
+        applicability: Applicability,
+    ) -> &mut Self {
+        self.suggestions.push(CodeSuggestion {
+            substitutions: suggestions
+                .into_iter()
+                .map(|suggestion| Substitution {
+                    parts: suggestion
+                        .into_iter()
+                        .map(|(span, snippet)| SubstitutionPart { snippet, span })
+                        .collect(),
+                })
+                .collect(),
+            msg: msg.to_owned(),
+            style: SuggestionStyle::ShowCode,
+            applicability,
+        });
+        self
+    }
+
     /// Prints out a message with for a multipart suggestion without showing the suggested code.
     ///
     /// This is intended to be used for suggestions that are obvious in what the changes need to

src/librustc_errors/diagnostic_builder.rs

@@ -260,6 +260,19 @@ impl<'a> DiagnosticBuilder<'a> {
         self
     }
 
+    pub fn multipart_suggestions(
+        &mut self,
+        msg: &str,
+        suggestions: Vec<Vec<(Span, String)>>,
+        applicability: Applicability,
+    ) -> &mut Self {
+        if !self.0.allow_suggestions {
+            return self;
+        }
+        self.0.diagnostic.multipart_suggestions(msg, suggestions, applicability);
+        self
+    }
+
     pub fn tool_only_multipart_suggestion(
         &mut self,
         msg: &str,

src/librustc_infer/infer/error_reporting/mod.rs

@@ -2037,8 +2037,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             self.tcx.sess,
             var_origin.span(),
             E0495,
-            "cannot infer an appropriate lifetime{} \
-             due to conflicting requirements",
+            "cannot infer an appropriate lifetime{} due to conflicting requirements",
             var_description
         )
     }