From 68147ebd603129c9f2c56bc47a5d2417a5df1777 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jakub=20Ber=C3=A1nek?= <berykubik@gmail.com>
Date: Fri, 17 Sep 2021 22:18:05 +0200
Subject: [PATCH] Suggest better place to add call parentheses for method
 expressions wrapped in parentheses

---
 compiler/rustc_typeck/src/check/expr.rs          | 16 +++++++++++++---
 compiler/rustc_typeck/src/check/method/mod.rs    |  3 ++-
 .../typeck/issue-89044-wrapped-expr-method.fixed |  9 +++++++++
 .../ui/typeck/issue-89044-wrapped-expr-method.rs |  9 +++++++++
 .../issue-89044-wrapped-expr-method.stderr       | 14 ++++++++++++++
 5 files changed, 47 insertions(+), 4 deletions(-)
 create mode 100644 src/test/ui/typeck/issue-89044-wrapped-expr-method.fixed
 create mode 100644 src/test/ui/typeck/issue-89044-wrapped-expr-method.rs
 create mode 100644 src/test/ui/typeck/issue-89044-wrapped-expr-method.stderr

diff --git a/compiler/rustc_typeck/src/check/expr.rs b/compiler/rustc_typeck/src/check/expr.rs
index 917adf0e2b9..1d08ecee558 100644
--- a/compiler/rustc_typeck/src/check/expr.rs
+++ b/compiler/rustc_typeck/src/check/expr.rs
@@ -1844,6 +1844,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 field,
                 expr_t,
                 expr,
+                None,
             );
         }
         err.emit();
@@ -1870,9 +1871,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             };
         let expr_snippet =
             self.tcx.sess.source_map().span_to_snippet(expr.span).unwrap_or(String::new());
-        if expr_is_call && expr_snippet.starts_with("(") && expr_snippet.ends_with(")") {
-            let after_open = expr.span.lo() + rustc_span::BytePos(1);
-            let before_close = expr.span.hi() - rustc_span::BytePos(1);
+        let is_wrapped = expr_snippet.starts_with("(") && expr_snippet.ends_with(")");
+        let after_open = expr.span.lo() + rustc_span::BytePos(1);
+        let before_close = expr.span.hi() - rustc_span::BytePos(1);
+
+        if expr_is_call && is_wrapped {
             err.multipart_suggestion(
                 "remove wrapping parentheses to call the method",
                 vec![
@@ -1882,12 +1885,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 Applicability::MachineApplicable,
             );
         } else if !self.expr_in_place(expr.hir_id) {
+            // Suggest call parentheses inside the wrapping parentheses
+            let span = if is_wrapped {
+                expr.span.with_lo(after_open).with_hi(before_close)
+            } else {
+                expr.span
+            };
             self.suggest_method_call(
                 &mut err,
                 "use parentheses to call the method",
                 field,
                 expr_t,
                 expr,
+                Some(span),
             );
         } else {
             err.help("methods are immutable and cannot be assigned to");
diff --git a/compiler/rustc_typeck/src/check/method/mod.rs b/compiler/rustc_typeck/src/check/method/mod.rs
index 2136d925423..8e09aa97dcf 100644
--- a/compiler/rustc_typeck/src/check/method/mod.rs
+++ b/compiler/rustc_typeck/src/check/method/mod.rs
@@ -141,6 +141,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         method_name: Ident,
         self_ty: Ty<'tcx>,
         call_expr: &hir::Expr<'_>,
+        span: Option<Span>,
     ) {
         let params = self
             .probe_for_name(
@@ -159,7 +160,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             .unwrap_or(0);
 
         // Account for `foo.bar<T>`;
-        let sugg_span = call_expr.span.shrink_to_hi();
+        let sugg_span = span.unwrap_or_else(|| call_expr.span).shrink_to_hi();
         let (suggestion, applicability) = (
             format!("({})", (0..params).map(|_| "_").collect::<Vec<_>>().join(", ")),
             if params > 0 { Applicability::HasPlaceholders } else { Applicability::MaybeIncorrect },
diff --git a/src/test/ui/typeck/issue-89044-wrapped-expr-method.fixed b/src/test/ui/typeck/issue-89044-wrapped-expr-method.fixed
new file mode 100644
index 00000000000..0a3086a345d
--- /dev/null
+++ b/src/test/ui/typeck/issue-89044-wrapped-expr-method.fixed
@@ -0,0 +1,9 @@
+// run-rustfix
+
+fn main() {
+    let a = Some(42);
+    println!(
+        "The value is {}.",
+        (a.unwrap()) //~ERROR [E0615]
+    );
+}
diff --git a/src/test/ui/typeck/issue-89044-wrapped-expr-method.rs b/src/test/ui/typeck/issue-89044-wrapped-expr-method.rs
new file mode 100644
index 00000000000..83617e035e9
--- /dev/null
+++ b/src/test/ui/typeck/issue-89044-wrapped-expr-method.rs
@@ -0,0 +1,9 @@
+// run-rustfix
+
+fn main() {
+    let a = Some(42);
+    println!(
+        "The value is {}.",
+        (a.unwrap) //~ERROR [E0615]
+    );
+}
diff --git a/src/test/ui/typeck/issue-89044-wrapped-expr-method.stderr b/src/test/ui/typeck/issue-89044-wrapped-expr-method.stderr
new file mode 100644
index 00000000000..6fa0915dcaf
--- /dev/null
+++ b/src/test/ui/typeck/issue-89044-wrapped-expr-method.stderr
@@ -0,0 +1,14 @@
+error[E0615]: attempted to take value of method `unwrap` on type `Option<{integer}>`
+  --> $DIR/issue-89044-wrapped-expr-method.rs:7:12
+   |
+LL |         (a.unwrap)
+   |            ^^^^^^ method, not a field
+   |
+help: use parentheses to call the method
+   |
+LL |         (a.unwrap())
+   |                  ++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0615`.