polish invisible-lifetimes lint: terminal-legibility and macro tolerance

zackmdavis · zackmdavis · commit 47aabb382259 · 2018-07-14T18:43:32.000-07:00
• The "indicate the anonymous lifetime: `'_,`" span label seemed at
   risk of being hard to read, even if it's not wrong. When we're
   splicing the anonymous lifetime into an already-existing set of
   angle-brackets like this, it's probably better to show the entire
   expression.

 • By using the path span instead of that of its final segment, we can
   (very) slightly simplify our code (by the amount of one less local
   variable), and handle at least some macro scenarios correctly (see
   `autowrapper!` in the UI test, which is a run-rustfix test)!

 • Another macro scenario (in type-annotation position) is observed to
   work.

This remains part of the grand endeavor of issue no. 52041!
diff --git a/src/librustc/middle/resolve_lifetime.rs b/src/librustc/middle/resolve_lifetime.rs
@@ -2109,16 +2109,15 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
         );
 
         if implicit_lifetimes.len() == 1 {
-            let segment_span = &path.segments[path.segments.len()-1].ident.span;
             let (replace_span,
                  suggestion) = if generic_args.args.len() == implicit_lifetimes.len() &&
                 generic_args.bindings.is_empty() {
                     // If there are no (non-implicit) generic args or bindings, our
                     // suggestion includes the angle brackets
-                    (segment_span.shrink_to_hi(), "<'_>")
+                    (path.span.shrink_to_hi(), "<'_>".to_owned())
                 } else {
                     // Otherwise—sorry, this is kind of gross—we need to infer the
-                    // replacement point span from the generics that do exist
+                    // place to splice in `'_, ` from the generics that do exist
                     let mut first_generic_span = None;
                     for ref arg in &generic_args.args {
                         match arg {
@@ -2143,9 +2142,18 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
                             break;
                         }
                     }
-                    let replace_span = first_generic_span
+                    let first_generic_span = first_generic_span
                         .expect("checked earlier that non-implicit args or bindings exist");
-                    (replace_span.shrink_to_lo(), "'_, ")
+                    // If our codemap can be trusted, construct the entire `Path<'_, T>` source
+                    // suggestion
+                    if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(path.span) {
+                        let (before, after) = snippet.split_at(
+                            (first_generic_span.lo().0 - path.span.lo().0) as usize
+                        );
+                        (path.span, format!("{}{}{}", before, "'_, ", after))
+                    } else {
+                        (first_generic_span.shrink_to_lo(), "'_, ".to_owned())
+                    }
                 };
             err.span_suggestion_with_applicability(
                 replace_span,
diff --git a/src/test/ui/in-band-lifetimes/elided-lifetimes.fixed b/src/test/ui/in-band-lifetimes/elided-lifetimes.fixed
@@ -46,10 +46,41 @@ fn wrap_gift_with_bow(gift: &str) -> WrappedWithBow<'_> {
     WrappedWithBow { gift }
 }
 
+macro_rules! autowrapper {
+    ($type_name:ident, $fn_name:ident, $lt:lifetime) => {
+        struct $type_name<$lt> {
+            gift: &$lt str
+        }
+
+        fn $fn_name(gift: &str) -> $type_name<'_> {
+            //~^ ERROR implicit lifetime parameters in types are deprecated
+            //~| HELP indicate the anonymous lifetime
+            $type_name { gift }
+        }
+    }
+}
+
+autowrapper!(Autowrapped, autowrap_gift, 'a);
+//~^ NOTE in this expansion of autowrapper!
+//~| NOTE in this expansion of autowrapper!
+
+macro_rules! anytuple_ref_ty {
+    ($($types:ty),*) => {
+        Ref<'_, ($($types),*)>
+        //~^ ERROR implicit lifetime parameters in types are deprecated
+        //~| HELP indicate the anonymous lifetime
+    }
+}
+
 fn main() {
     let honesty = RefCell::new((4, 'e'));
     let loyalty: Ref<'_, (u32, char)> = honesty.borrow();
     //~^ ERROR implicit lifetime parameters in types are deprecated
     //~| HELP indicate the anonymous lifetime
     let generosity = Ref::map(loyalty, |t| &t.0);
+
+    let laughter = RefCell::new((true, "magic"));
+    let yellow: anytuple_ref_ty!(bool, &str) = laughter.borrow();
+    //~^ NOTE in this expansion of anytuple_ref_ty!
+    //~| NOTE in this expansion of anytuple_ref_ty!
 }
diff --git a/src/test/ui/in-band-lifetimes/elided-lifetimes.rs b/src/test/ui/in-band-lifetimes/elided-lifetimes.rs
@@ -46,10 +46,41 @@ fn wrap_gift_with_bow(gift: &str) -> WrappedWithBow {
     WrappedWithBow { gift }
 }
 
+macro_rules! autowrapper {
+    ($type_name:ident, $fn_name:ident, $lt:lifetime) => {
+        struct $type_name<$lt> {
+            gift: &$lt str
+        }
+
+        fn $fn_name(gift: &str) -> $type_name {
+            //~^ ERROR implicit lifetime parameters in types are deprecated
+            //~| HELP indicate the anonymous lifetime
+            $type_name { gift }
+        }
+    }
+}
+
+autowrapper!(Autowrapped, autowrap_gift, 'a);
+//~^ NOTE in this expansion of autowrapper!
+//~| NOTE in this expansion of autowrapper!
+
+macro_rules! anytuple_ref_ty {
+    ($($types:ty),*) => {
+        Ref<($($types),*)>
+        //~^ ERROR implicit lifetime parameters in types are deprecated
+        //~| HELP indicate the anonymous lifetime
+    }
+}
+
 fn main() {
     let honesty = RefCell::new((4, 'e'));
     let loyalty: Ref<(u32, char)> = honesty.borrow();
     //~^ ERROR implicit lifetime parameters in types are deprecated
     //~| HELP indicate the anonymous lifetime
     let generosity = Ref::map(loyalty, |t| &t.0);
+
+    let laughter = RefCell::new((true, "magic"));
+    let yellow: anytuple_ref_ty!(bool, &str) = laughter.borrow();
+    //~^ NOTE in this expansion of anytuple_ref_ty!
+    //~| NOTE in this expansion of anytuple_ref_ty!
 }
diff --git a/src/test/ui/in-band-lifetimes/elided-lifetimes.stderr b/src/test/ui/in-band-lifetimes/elided-lifetimes.stderr
@@ -23,12 +23,28 @@ LL | fn wrap_gift_with_bow(gift: &str) -> WrappedWithBow {
    |                                      ^^^^^^^^^^^^^^- help: indicate the anonymous lifetime: `<'_>`
 
 error: implicit lifetime parameters in types are deprecated
-  --> $DIR/elided-lifetimes.rs:51:18
+  --> $DIR/elided-lifetimes.rs:77:18
    |
 LL |     let loyalty: Ref<(u32, char)> = honesty.borrow();
-   |                  ^^^^-^^^^^^^^^^^
-   |                      |
-   |                      help: indicate the anonymous lifetime: `'_,`
+   |                  ^^^^^^^^^^^^^^^^ help: indicate the anonymous lifetime: `Ref<'_, (u32, char)>`
 
-error: aborting due to 4 previous errors
+error: implicit lifetime parameters in types are deprecated
+  --> $DIR/elided-lifetimes.rs:69:9
+   |
+LL |         Ref<($($types),*)>
+   |         ^^^^^^^^^^^^^^^^^^ help: indicate the anonymous lifetime: `Ref<'_, ($($types),*)>`
+...
+LL |     let yellow: anytuple_ref_ty!(bool, &str) = laughter.borrow();
+   |                 ---------------------------- in this macro invocation
+
+error: implicit lifetime parameters in types are deprecated
+  --> $DIR/elided-lifetimes.rs:55:36
+   |
+LL |         fn $fn_name(gift: &str) -> $type_name {
+   |                                    ^^^^^^^^^^- help: indicate the anonymous lifetime: `<'_>`
+...
+LL | autowrapper!(Autowrapped, autowrap_gift, 'a);
+   | --------------------------------------------- in this macro invocation
+
+error: aborting due to 6 previous errors
 
