From 7fef1628735622ad005245ea2294449720ba7c5c Mon Sep 17 00:00:00 2001
From: Nick Hamann <nick@wabbo.org>
Date: Wed, 18 May 2016 00:02:04 -0500
Subject: [PATCH 1/2] Only print parameters with elided lifetimes in elision
 error messages.

When displaying the function parameters for a lifetime elision error message,
this changes it to first filter out the parameters that don't have elided
lifetimes.

Fixes #30255.
---
 src/librustc_typeck/astconv.rs       | 26 ++++++++++++++-------
 src/test/compile-fail/issue-30255.rs | 35 ++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 8 deletions(-)
 create mode 100644 src/test/compile-fail/issue-30255.rs

diff --git a/src/librustc_typeck/astconv.rs b/src/librustc_typeck/astconv.rs
index 4faefb610562..c3633625436a 100644
--- a/src/librustc_typeck/astconv.rs
+++ b/src/librustc_typeck/astconv.rs
@@ -215,15 +215,24 @@ fn report_elision_failure(
 {
     let mut m = String::new();
     let len = params.len();
-    let mut any_lifetimes = false;
 
-    for (i, info) in params.into_iter().enumerate() {
+    let elided_params: Vec<_> = params.into_iter()
+                                       .filter(|info| info.lifetime_count > 0)
+                                       .collect();
+
+    let elided_len = elided_params.len();
+
+    let any_lifetimes = if elided_len > 0 {
+        true
+    } else {
+        false
+    };
+
+    for (i, info) in elided_params.into_iter().enumerate() {
         let ElisionFailureInfo {
             name, lifetime_count: n, have_bound_regions
         } = info;
 
-        any_lifetimes = any_lifetimes || (n > 0);
-
         let help_name = if name.is_empty() {
             format!("argument {}", i + 1)
         } else {
@@ -237,13 +246,14 @@ fn report_elision_failure(
                     if have_bound_regions { "free " } else { "" } )
         })[..]);
 
-        if len == 2 && i == 0 {
+        if elided_len == 2 && i == 0 {
             m.push_str(" or ");
-        } else if i + 2 == len {
+        } else if i + 2 == elided_len {
             m.push_str(", or ");
-        } else if i + 1 != len {
+        } else if i != elided_len - 1 {
             m.push_str(", ");
         }
+
     }
 
     if len == 0 {
@@ -260,7 +270,7 @@ fn report_elision_failure(
         help!(db,
                    "consider giving it an explicit bounded or 'static \
                     lifetime");
-    } else if len == 1 {
+    } else if elided_len == 1 {
         help!(db,
                    "this function's return type contains a borrowed value, but \
                     the signature does not say which {} it is borrowed from",
diff --git a/src/test/compile-fail/issue-30255.rs b/src/test/compile-fail/issue-30255.rs
new file mode 100644
index 000000000000..1daa6a61f777
--- /dev/null
+++ b/src/test/compile-fail/issue-30255.rs
@@ -0,0 +1,35 @@
+// Copyright 2016 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.
+//
+// Test that lifetime elision error messages correctly omit parameters
+// with no elided lifetimes
+
+struct S<'a> {
+    field: &'a i32,
+}
+
+fn f(a: &S, b: i32) -> &i32 {
+//~^ ERROR missing lifetime specifier [E0106]
+//~^^ HELP does not say which one of `a`'s 2 elided lifetimes it is borrowed from
+    panic!();
+}
+
+fn g(a: &S, b: bool, c: &i32) -> &i32 {
+//~^ ERROR missing lifetime specifier [E0106]
+//~^^ HELP does not say whether it is borrowed from one of `a`'s 2 elided lifetimes or `c`
+    panic!();
+}
+
+fn h(a: &bool, b: bool, c: &S, d: &i32) -> &i32 {
+//~^ ERROR missing lifetime specifier [E0106]
+//~^^ HELP does not say whether it is borrowed from `a`, one of `c`'s 2 elided lifetimes, or `d`
+    panic!();
+}
+

From a50c82bc3bde5988a8f32ef2b593f0b051545e8a Mon Sep 17 00:00:00 2001
From: Nick Hamann <nick@wabbo.org>
Date: Wed, 18 May 2016 13:09:25 -0500
Subject: [PATCH 2/2] Simplify report_elision_failure a little bit.

---
 src/librustc_typeck/astconv.rs | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/src/librustc_typeck/astconv.rs b/src/librustc_typeck/astconv.rs
index c3633625436a..8fc6b552e146 100644
--- a/src/librustc_typeck/astconv.rs
+++ b/src/librustc_typeck/astconv.rs
@@ -222,12 +222,6 @@ fn report_elision_failure(
 
     let elided_len = elided_params.len();
 
-    let any_lifetimes = if elided_len > 0 {
-        true
-    } else {
-        false
-    };
-
     for (i, info) in elided_params.into_iter().enumerate() {
         let ElisionFailureInfo {
             name, lifetime_count: n, have_bound_regions
@@ -262,7 +256,7 @@ fn report_elision_failure(
                     there is no value for it to be borrowed from");
         help!(db,
                    "consider giving it a 'static lifetime");
-    } else if !any_lifetimes {
+    } else if elided_len == 0 {
         help!(db,
                    "this function's return type contains a borrowed value with \
                     an elided lifetime, but the lifetime cannot be derived from \