From 6d5f9478b22da27dc59d204cf94060bf949b6746 Mon Sep 17 00:00:00 2001
From: Georg Brandl <georg@python.org>
Date: Wed, 12 Aug 2015 07:48:00 +0200
Subject: [PATCH] utils: implement if_let_chain macro as suggested by isHavvy

---
 src/lib.rs     |  3 ++-
 src/returns.rs | 26 ++++++++++++--------------
 src/utils.rs   | 29 +++++++++++++++++++++++++++++
 3 files changed, 43 insertions(+), 15 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index c5469c198..fef678f66 100755
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -13,6 +13,8 @@ extern crate collections;
 use rustc::plugin::Registry;
 use rustc::lint::LintPassObject;
 
+#[macro_use]
+pub mod utils;
 pub mod types;
 pub mod misc;
 pub mod eq_op;
@@ -27,7 +29,6 @@ pub mod len_zero;
 pub mod attrs;
 pub mod collapsible_if;
 pub mod unicode;
-pub mod utils;
 pub mod strings;
 pub mod methods;
 pub mod returns;
diff --git a/src/returns.rs b/src/returns.rs
index 9bfc99972..5a361d3a7 100644
--- a/src/returns.rs
+++ b/src/returns.rs
@@ -67,20 +67,18 @@ impl ReturnPass {
     // Check for "let x = EXPR; x"
     fn check_let_return(&mut self, cx: &Context, block: &Block) {
         // we need both a let-binding stmt and an expr
-        if let Some(stmt) = block.stmts.last() {
-            if let StmtDecl(ref decl, _) = stmt.node {
-                if let DeclLocal(ref local) = decl.node {
-                    if let Some(ref initexpr) = local.init {
-                        if let PatIdent(_, Spanned { node: id, .. }, _) = local.pat.node {
-                            if let Some(ref retexpr) = block.expr {
-                                if let ExprPath(_, ref path) = retexpr.node {
-                                    if match_path(path, &[&*id.name.as_str()]) {
-                                        self.emit_let_lint(cx, retexpr.span, initexpr.span);
-                                    }
-                                }
-                            }
-                        }
-                    }
+        if_let_chain! {
+            [
+                Some(stmt) = block.stmts.last(),
+                StmtDecl(ref decl, _) = stmt.node,
+                DeclLocal(ref local) = decl.node,
+                Some(ref initexpr) = local.init,
+                PatIdent(_, Spanned { node: id, .. }, _) = local.pat.node,
+                Some(ref retexpr) = block.expr,
+                ExprPath(_, ref path) = retexpr.node
+            ], {
+                if match_path(path, &[&*id.name.as_str()]) {
+                    self.emit_let_lint(cx, retexpr.span, initexpr.span);
                 }
             }
         }
diff --git a/src/utils.rs b/src/utils.rs
index 107f5c6f9..575d39b0c 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -92,3 +92,32 @@ pub fn walk_ptrs_ty<'t>(ty: ty::Ty<'t>) -> ty::Ty<'t> {
         _ => ty
     }
 }
+
+/// Produce a nested chain of if-lets from the patterns:
+///
+///     if_let_chain! {[Some(y) = x, Some(z) = y],
+///         {
+///             block
+///         }
+///     }
+///
+/// becomes
+///
+///     if let Some(y) = x {
+///         if let Some(z) = y {
+///             block
+///         }
+///     }
+#[macro_export]
+macro_rules! if_let_chain {
+    ([$pat:pat = $expr:expr, $($p2:pat = $e2:expr),+], $block:block) => {
+        if let $pat = $expr {
+           if_let_chain!{ [$($p2 = $e2),+], $block }
+        }
+    };
+    ([$pat:pat = $expr:expr], $block:block) => {
+        if let $pat = $expr {
+           $block
+        }
+    };
+}