From d3c06f7252fdca30b19aa6ff8ecf63c86675676e Mon Sep 17 00:00:00 2001
From: Joshua Holmer <jholmer@dminc.com>
Date: Fri, 12 Oct 2018 10:26:55 -0400
Subject: [PATCH 1/3] Exclude pattern guards from unnecessary_fold lint

Methods like `Iterator::any` borrow the iterator mutably,
which is not allowed within a pattern guard and will fail to compile.
This commit prevents clippy from suggesting this type of change.

Closes #3069
---
 clippy_lints/src/methods/mod.rs | 18 ++++++++++++++++++
 tests/ui/unnecessary_fold.rs    |  7 +++++++
 2 files changed, 25 insertions(+)

diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index 7c15eb677cc..66c94746f5a 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -9,6 +9,7 @@
 
 
 use crate::rustc::hir;
+use crate::rustc::hir::{ExprKind, Guard, Node};
 use crate::rustc::hir::def::Def;
 use crate::rustc::lint::{in_external_macro, LateContext, LateLintPass, Lint, LintArray, LintContext, LintPass};
 use crate::rustc::ty::{self, Ty};
@@ -1428,6 +1429,23 @@ fn lint_unnecessary_fold(cx: &LateContext<'_, '_>, expr: &hir::Expr, fold_args:
         return;
     }
 
+    // `Iterator::any` cannot be used within a pattern guard
+    // See https://github.com/rust-lang-nursery/rust-clippy/issues/3069
+    if_chain! {
+        if let Some(fold_parent) = cx.tcx.hir.find(cx.tcx.hir.get_parent_node(expr.id));
+        if let Node::Expr(fold_parent) = fold_parent;
+        if let ExprKind::Match(_, ref arms, _) = fold_parent.node;
+        if arms.iter().any(|arm| {
+            if let Some(Guard::If(ref guard)) = arm.guard {
+                return guard.id == expr.id;
+            }
+            false
+        });
+        then {
+            return;
+        }
+    }
+
     assert!(fold_args.len() == 3,
         "Expected fold_args to have three entries - the receiver, the initial value and the closure");
 
diff --git a/tests/ui/unnecessary_fold.rs b/tests/ui/unnecessary_fold.rs
index e8d84ecea8c..3b70602d4ad 100644
--- a/tests/ui/unnecessary_fold.rs
+++ b/tests/ui/unnecessary_fold.rs
@@ -45,6 +45,13 @@ fn unnecessary_fold_should_ignore() {
 
     let _ = [(0..2), (0..3)].iter().fold(0, |a, b| a + b.len());
     let _ = [(0..2), (0..3)].iter().fold(1, |a, b| a * b.len());
+
+    // Because `any` takes the iterator as a mutable reference,
+    // it cannot be used in a pattern guard, and we must use `fold`.
+    match 1 {
+        _ if (0..3).fold(false, |acc, x| acc || x > 2) => {}
+        _ => {}
+    }
 }
 
 fn main() {}

From 863c8e26fc66e856456cb05e75e1d6c821a04ec6 Mon Sep 17 00:00:00 2001
From: Joshua Holmer <jholmer@dminc.com>
Date: Fri, 12 Oct 2018 13:15:55 -0400
Subject: [PATCH 2/3] Revert "Exclude pattern guards from unnecessary_fold
 lint"

This reverts commit d3c06f7252fdca30b19aa6ff8ecf63c86675676e.
---
 clippy_lints/src/methods/mod.rs | 18 ------------------
 tests/ui/unnecessary_fold.rs    |  7 -------
 2 files changed, 25 deletions(-)

diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index 66c94746f5a..7c15eb677cc 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -9,7 +9,6 @@
 
 
 use crate::rustc::hir;
-use crate::rustc::hir::{ExprKind, Guard, Node};
 use crate::rustc::hir::def::Def;
 use crate::rustc::lint::{in_external_macro, LateContext, LateLintPass, Lint, LintArray, LintContext, LintPass};
 use crate::rustc::ty::{self, Ty};
@@ -1429,23 +1428,6 @@ fn lint_unnecessary_fold(cx: &LateContext<'_, '_>, expr: &hir::Expr, fold_args:
         return;
     }
 
-    // `Iterator::any` cannot be used within a pattern guard
-    // See https://github.com/rust-lang-nursery/rust-clippy/issues/3069
-    if_chain! {
-        if let Some(fold_parent) = cx.tcx.hir.find(cx.tcx.hir.get_parent_node(expr.id));
-        if let Node::Expr(fold_parent) = fold_parent;
-        if let ExprKind::Match(_, ref arms, _) = fold_parent.node;
-        if arms.iter().any(|arm| {
-            if let Some(Guard::If(ref guard)) = arm.guard {
-                return guard.id == expr.id;
-            }
-            false
-        });
-        then {
-            return;
-        }
-    }
-
     assert!(fold_args.len() == 3,
         "Expected fold_args to have three entries - the receiver, the initial value and the closure");
 
diff --git a/tests/ui/unnecessary_fold.rs b/tests/ui/unnecessary_fold.rs
index 3b70602d4ad..e8d84ecea8c 100644
--- a/tests/ui/unnecessary_fold.rs
+++ b/tests/ui/unnecessary_fold.rs
@@ -45,13 +45,6 @@ fn unnecessary_fold_should_ignore() {
 
     let _ = [(0..2), (0..3)].iter().fold(0, |a, b| a + b.len());
     let _ = [(0..2), (0..3)].iter().fold(1, |a, b| a * b.len());
-
-    // Because `any` takes the iterator as a mutable reference,
-    // it cannot be used in a pattern guard, and we must use `fold`.
-    match 1 {
-        _ if (0..3).fold(false, |acc, x| acc || x > 2) => {}
-        _ => {}
-    }
 }
 
 fn main() {}

From 33847b579eb5479f888a0caae37ebc469dd9ccd2 Mon Sep 17 00:00:00 2001
From: Joshua Holmer <jholmer@dminc.com>
Date: Tue, 16 Oct 2018 09:04:02 -0400
Subject: [PATCH 3/3] Update known problems for unnecessary_fold

---
 clippy_lints/src/methods/mod.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index 7c15eb677cc..6fc563a42ea 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -688,7 +688,8 @@ declare_clippy_lint! {
 ///
 /// **Why is this bad?** Readability.
 ///
-/// **Known problems:** None.
+/// **Known problems:** False positive in pattern guards. Will be resolved once
+/// non-lexical lifetimes are stable.
 ///
 /// **Example:**
 /// ```rust