Fix `impl trait where` without `impl where`

4 files changed, 35 insertions, 7 deletions

diff --git a/Cargo.toml b/Cargo.toml
index 6f7645d..d606dd9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "impl_trait"
-version = "0.1.5"
+version = "0.1.6"
 authors = ["SoniEx2 <endermoneymod@gmail.com>"]
 edition = "2018"
 description = "Allows impl trait inside inherent impl."
diff --git a/src/lib.rs b/src/lib.rs
index 192d56b..348e4e1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -210,14 +210,16 @@ pub fn impl_trait(item: TokenStream) -> TokenStream {
                         // *then* add the "where" (from the impl-trait)
                         found.last_mut().unwrap().push(tt.clone());
                         // and the parent bounds (except the "where")
-                        found.last_mut().unwrap().extend((&where_bounds).into_iter().skip(1).cloned());
-                        // also make sure that there's an ',' at the correct place
-                        if let Some(&TokenTree::Punct(ref x)) = where_bounds.last() {
-                            if x.as_char() == ',' {
-                                continue 'main_loop;
+                        if !where_bounds.is_empty() {
+                            found.last_mut().unwrap().extend((&where_bounds).into_iter().skip(1).cloned());
+                            // also make sure that there's an ',' at the correct place
+                            if let Some(&TokenTree::Punct(ref x)) = where_bounds.last() {
+                                if x.as_char() == ',' {
+                                    continue 'main_loop;
+                                }
                             }
+                            found.last_mut().unwrap().push(proc_macro::Punct::new(',', proc_macro::Spacing::Alone).into());
                         }
-                        found.last_mut().unwrap().push(proc_macro::Punct::new(',', proc_macro::Spacing::Alone).into());
                         continue 'main_loop;
                     }
                 }
diff --git a/tests/14-where-on-trait.rs b/tests/14-where-on-trait.rs
new file mode 100644
index 0000000..56c7a4a
--- /dev/null
+++ b/tests/14-where-on-trait.rs
@@ -0,0 +1,25 @@
+// Checks that the impl trait can have where.
+
+use impl_trait::impl_trait;
+
+struct Foo<T>(T);
+trait Bar<U> {
+}
+
+impl_trait! {
+    impl<T> Foo<T> {
+        impl trait<U> Bar<U> where Self: From<U> {
+        }
+    }
+}
+impl From<()> for Foo<()> {
+    fn from(x: ()) -> Self {
+        Self { 0: x }
+    }
+}
+
+fn static_assert_1<T: Bar<U>, U>(_t: T, _u: U) {}
+
+fn main() {
+    static_assert_1(Foo(()), ());
+}
diff --git a/tests/progress.rs b/tests/progress.rs
index ef302b0..1cece81 100644
--- a/tests/progress.rs
+++ b/tests/progress.rs
@@ -14,6 +14,7 @@ fn tests() {
     t.pass("tests/11-traits-generics-docs.rs");
     t.pass("tests/12-combining-generics.rs");
     t.pass("tests/13-trait-generics.rs");
+    t.pass("tests/14-where-on-trait.rs");
     t.pass("tests/98-readme.rs");
     t.pass("tests/99-goal.rs");
 }