From 5a813b6dd66d8056c62d268479c0b27dcd697554 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Arthur=20Woimb=C3=A9e?= <arthur.woimbee@gmail.com>
Date: Wed, 27 May 2020 18:31:22 +0200
Subject: [PATCH 1/2] Fix missing parentheses Fn notation error

---
 src/librustc_typeck/astconv.rs | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/librustc_typeck/astconv.rs b/src/librustc_typeck/astconv.rs
index 12edfed19c07e..ab9db159038af 100644
--- a/src/librustc_typeck/astconv.rs
+++ b/src/librustc_typeck/astconv.rs
@@ -1151,9 +1151,16 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                             .as_ref()
                             .and_then(|args| args.args.get(0))
                             .and_then(|arg| match arg {
-                                hir::GenericArg::Type(ty) => {
-                                    sess.source_map().span_to_snippet(ty.span).ok()
+                                hir::GenericArg::Type(ty) => match ty.kind {
+                                    hir::TyKind::Tup(t) => t
+                                        .iter()
+                                        .map(|e| sess.source_map().span_to_snippet(e.span))
+                                        .collect::<Result<Vec<_>, _>>()
+                                        .map(|a| a.join(", ")),
+                                    _ => sess.source_map().span_to_snippet(ty.span),
                                 }
+                                .map(|s| format!("({})", s))
+                                .ok(),
                                 _ => None,
                             })
                             .unwrap_or_else(|| "()".to_string()),

From c54d4fe93f1640fee0be7bfe9c525938dde558e8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Arthur=20Woimb=C3=A9e?= <arthur.woimbee@gmail.com>
Date: Sat, 30 May 2020 18:29:45 +0200
Subject: [PATCH 2/2] Test ui suggestion fn trait notation

---
 .../ui/suggestions/fn-trait-notation.fixed    | 19 ++++++++++++
 src/test/ui/suggestions/fn-trait-notation.rs  | 19 ++++++++++++
 .../ui/suggestions/fn-trait-notation.stderr   | 30 +++++++++++++++++++
 3 files changed, 68 insertions(+)
 create mode 100644 src/test/ui/suggestions/fn-trait-notation.fixed
 create mode 100644 src/test/ui/suggestions/fn-trait-notation.rs
 create mode 100644 src/test/ui/suggestions/fn-trait-notation.stderr

diff --git a/src/test/ui/suggestions/fn-trait-notation.fixed b/src/test/ui/suggestions/fn-trait-notation.fixed
new file mode 100644
index 0000000000000..cf940f4e9267a
--- /dev/null
+++ b/src/test/ui/suggestions/fn-trait-notation.fixed
@@ -0,0 +1,19 @@
+// run-rustfix
+fn e0658<F, G, H>(f: F, g: G, h: H) -> i32
+where
+    F: Fn(i32) -> i32, //~ ERROR E0658
+    G: Fn(i32, i32) -> (i32, i32), //~ ERROR E0658
+    H: Fn(i32) -> i32, //~ ERROR E0658
+{
+    f(3);
+    g(3, 4);
+    h(3)
+}
+
+fn main() {
+    e0658(
+        |a| a,
+        |a, b| (b, a),
+        |a| a,
+    );
+}
diff --git a/src/test/ui/suggestions/fn-trait-notation.rs b/src/test/ui/suggestions/fn-trait-notation.rs
new file mode 100644
index 0000000000000..f0bb03315d987
--- /dev/null
+++ b/src/test/ui/suggestions/fn-trait-notation.rs
@@ -0,0 +1,19 @@
+// run-rustfix
+fn e0658<F, G, H>(f: F, g: G, h: H) -> i32
+where
+    F: Fn<i32, Output = i32>, //~ ERROR E0658
+    G: Fn<(i32, i32, ), Output = (i32, i32)>, //~ ERROR E0658
+    H: Fn<(i32,), Output = i32>, //~ ERROR E0658
+{
+    f(3);
+    g(3, 4);
+    h(3)
+}
+
+fn main() {
+    e0658(
+        |a| a,
+        |a, b| (b, a),
+        |a| a,
+    );
+}
diff --git a/src/test/ui/suggestions/fn-trait-notation.stderr b/src/test/ui/suggestions/fn-trait-notation.stderr
new file mode 100644
index 0000000000000..3e3b541744017
--- /dev/null
+++ b/src/test/ui/suggestions/fn-trait-notation.stderr
@@ -0,0 +1,30 @@
+error[E0658]: the precise format of `Fn`-family traits' type parameters is subject to change
+  --> $DIR/fn-trait-notation.rs:4:8
+   |
+LL |     F: Fn<i32, Output = i32>,
+   |        ^^^^^^^^^^^^^^^^^^^^^ help: use parenthetical notation instead: `Fn(i32) -> i32`
+   |
+   = note: see issue #29625 <https://github.com/rust-lang/rust/issues/29625> for more information
+   = help: add `#![feature(unboxed_closures)]` to the crate attributes to enable
+
+error[E0658]: the precise format of `Fn`-family traits' type parameters is subject to change
+  --> $DIR/fn-trait-notation.rs:5:8
+   |
+LL |     G: Fn<(i32, i32, ), Output = (i32, i32)>,
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use parenthetical notation instead: `Fn(i32, i32) -> (i32, i32)`
+   |
+   = note: see issue #29625 <https://github.com/rust-lang/rust/issues/29625> for more information
+   = help: add `#![feature(unboxed_closures)]` to the crate attributes to enable
+
+error[E0658]: the precise format of `Fn`-family traits' type parameters is subject to change
+  --> $DIR/fn-trait-notation.rs:6:8
+   |
+LL |     H: Fn<(i32,), Output = i32>,
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^ help: use parenthetical notation instead: `Fn(i32) -> i32`
+   |
+   = note: see issue #29625 <https://github.com/rust-lang/rust/issues/29625> for more information
+   = help: add `#![feature(unboxed_closures)]` to the crate attributes to enable
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0658`.