From 97d47a5e7c41274eacbec55a4c08112407c78ff5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Sat, 8 Feb 2020 20:02:54 -0800
Subject: [PATCH] Account for type params on method without parens

---
 src/librustc_typeck/check/expr.rs              |  4 ++--
 src/librustc_typeck/check/method/mod.rs        | 18 +++++++++++++-----
 .../suggestions/method-missing-parentheses.rs  |  5 +++++
 .../method-missing-parentheses.stderr          | 17 +++++++++++++++++
 4 files changed, 37 insertions(+), 7 deletions(-)
 create mode 100644 src/test/ui/suggestions/method-missing-parentheses.rs
 create mode 100644 src/test/ui/suggestions/method-missing-parentheses.stderr

diff --git a/src/librustc_typeck/check/expr.rs b/src/librustc_typeck/check/expr.rs
index 9ce89bd636304..90b7b300da9d5 100644
--- a/src/librustc_typeck/check/expr.rs
+++ b/src/librustc_typeck/check/expr.rs
@@ -1586,7 +1586,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 &format!("a method `{}` also exists, call it with parentheses", field),
                 field,
                 expr_t,
-                expr.hir_id,
+                expr,
             );
         }
         err.emit();
@@ -1609,7 +1609,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 "use parentheses to call the method",
                 field,
                 expr_t,
-                expr.hir_id,
+                expr,
             );
         } else {
             err.help("methods are immutable and cannot be assigned to");
diff --git a/src/librustc_typeck/check/method/mod.rs b/src/librustc_typeck/check/method/mod.rs
index e90c2ef5e4361..a75154b160a5c 100644
--- a/src/librustc_typeck/check/method/mod.rs
+++ b/src/librustc_typeck/check/method/mod.rs
@@ -135,7 +135,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         msg: &str,
         method_name: ast::Ident,
         self_ty: Ty<'tcx>,
-        call_expr_id: hir::HirId,
+        call_expr: &hir::Expr<'_>,
     ) {
         let has_params = self
             .probe_for_name(
@@ -144,7 +144,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 method_name,
                 IsSuggestion(false),
                 self_ty,
-                call_expr_id,
+                call_expr.hir_id,
                 ProbeScope::TraitsInScope,
             )
             .and_then(|pick| {
@@ -152,13 +152,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 Ok(sig.inputs().skip_binder().len() > 1)
             });
 
+        // Account for `foo.bar<T>`;
+        let sugg_span = method_name.span.with_hi(call_expr.span.hi());
+        let snippet = self
+            .tcx
+            .sess
+            .source_map()
+            .span_to_snippet(sugg_span)
+            .unwrap_or_else(|_| method_name.to_string());
         let (suggestion, applicability) = if has_params.unwrap_or_default() {
-            (format!("{}(...)", method_name), Applicability::HasPlaceholders)
+            (format!("{}(...)", snippet), Applicability::HasPlaceholders)
         } else {
-            (format!("{}()", method_name), Applicability::MaybeIncorrect)
+            (format!("{}()", snippet), Applicability::MaybeIncorrect)
         };
 
-        err.span_suggestion(method_name.span, msg, suggestion, applicability);
+        err.span_suggestion(sugg_span, msg, suggestion, applicability);
     }
 
     /// Performs method lookup. If lookup is successful, it will return the callee
diff --git a/src/test/ui/suggestions/method-missing-parentheses.rs b/src/test/ui/suggestions/method-missing-parentheses.rs
new file mode 100644
index 0000000000000..e1a85271ad0a3
--- /dev/null
+++ b/src/test/ui/suggestions/method-missing-parentheses.rs
@@ -0,0 +1,5 @@
+fn main() {
+    let _ = vec![].into_iter().collect::<usize>;
+    //~^ ERROR attempted to take value of method `collect` on type `std::vec::IntoIter<_>`
+    //~| ERROR field expressions may not have generic arguments
+}
diff --git a/src/test/ui/suggestions/method-missing-parentheses.stderr b/src/test/ui/suggestions/method-missing-parentheses.stderr
new file mode 100644
index 0000000000000..8569eb6f4ad1e
--- /dev/null
+++ b/src/test/ui/suggestions/method-missing-parentheses.stderr
@@ -0,0 +1,17 @@
+error: field expressions may not have generic arguments
+  --> $DIR/method-missing-parentheses.rs:2:41
+   |
+LL |     let _ = vec![].into_iter().collect::<usize>;
+   |                                         ^^^^^^^
+
+error[E0615]: attempted to take value of method `collect` on type `std::vec::IntoIter<_>`
+  --> $DIR/method-missing-parentheses.rs:2:32
+   |
+LL |     let _ = vec![].into_iter().collect::<usize>;
+   |                                ^^^^^^^---------
+   |                                |
+   |                                help: use parentheses to call the method: `collect::<usize>()`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0615`.