From 7e3efaf6c5c3ba5f28dcc8854ae1e551664c09f8 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Mon, 7 May 2018 21:15:21 -0700
Subject: [PATCH] Improve error when a 'de lifetime parameter already exists

---
 serde_derive/src/de.rs                           | 16 ++++++++++++++++
 .../precondition/deserialize_de_lifetime.rs      | 15 +++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 test_suite/tests/compile-fail/precondition/deserialize_de_lifetime.rs

diff --git a/serde_derive/src/de.rs b/serde_derive/src/de.rs
index e88d1dd8..73c15b02 100644
--- a/serde_derive/src/de.rs
+++ b/serde_derive/src/de.rs
@@ -82,6 +82,11 @@ pub fn expand_derive_deserialize(input: &syn::DeriveInput) -> Result<Tokens, Str
 }
 
 fn precondition(cx: &Ctxt, cont: &Container) {
+    precondition_sized(cx, cont);
+    precondition_no_de_lifetime(cx, cont);
+}
+
+fn precondition_sized(cx: &Ctxt, cont: &Container) {
     if let Data::Struct(_, ref fields) = cont.data {
         if let Some(last) = fields.last() {
             if let syn::Type::Slice(_) = *last.ty {
@@ -91,6 +96,17 @@ fn precondition(cx: &Ctxt, cont: &Container) {
     }
 }
 
+fn precondition_no_de_lifetime(cx: &Ctxt, cont: &Container) {
+    if let BorrowedLifetimes::Borrowed(_) = borrowed_lifetimes(cont) {
+        for param in cont.generics.lifetimes() {
+            if param.lifetime.to_string() == "'de" {
+                cx.error("cannot deserialize when there is a lifetime parameter called 'de");
+                return;
+            }
+        }
+    }
+}
+
 struct Parameters {
     /// Name of the type the `derive` is on.
     local: syn::Ident,
diff --git a/test_suite/tests/compile-fail/precondition/deserialize_de_lifetime.rs b/test_suite/tests/compile-fail/precondition/deserialize_de_lifetime.rs
new file mode 100644
index 00000000..4ab2f6a3
--- /dev/null
+++ b/test_suite/tests/compile-fail/precondition/deserialize_de_lifetime.rs
@@ -0,0 +1,15 @@
+// Copyright 2018 Serde Developers
+//
+// 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.
+
+#[macro_use]
+extern crate serde_derive;
+
+#[derive(Deserialize)] //~ ERROR: proc-macro derive panicked
+struct S<'de> {
+    s: &'de str, //~^^ HELP: cannot deserialize when there is a lifetime parameter called 'de
+}