Add a ui test with ambiguous quote_spanned span

tests/ui/ambiguous-span.rs

@@ -0,0 +1,16 @@
+use proc_macro2::Span;
+use quote::quote_spanned;
+
+trait CallSite {
+    fn get() -> Self;
+}
+
+impl CallSite for Span {
+    fn get() -> Self {
+        Span::call_site()
+    }
+}
+
+fn main() {
+    let _ = quote_spanned!(CallSite::get()=> ...);
+}

tests/ui/ambiguous-span.stderr

@@ -0,0 +1,13 @@
+error[E0283]: type annotations needed
+  --> tests/ui/ambiguous-span.rs:15:28
+   |
+15 |     let _ = quote_spanned!(CallSite::get()=> ...);
+   |             ---------------^^^^^^^^^^^^^^^-------
+   |             |              |
+   |             |              cannot infer type
+   |             required by a bound introduced by this call
+   |
+   = note: cannot satisfy `_: IntoSpan`
+   = help: the following types implement trait `IntoSpan`:
+             DelimSpan
+             Span