add_type_neq_err_label: don't .unwrap

src/librustc_typeck/check/op.rs

@@ -481,7 +481,7 @@ fn check_overloaded_binop(
     }
 
     /// If one of the types is an uncalled function and calling it would yield the other type,
-    /// suggest calling the function. Returns whether a suggestion was given.
+    /// suggest calling the function. Returns `true` if suggestion would apply (even if not given).
     fn add_type_neq_err_label(
         &self,
         err: &mut rustc_errors::DiagnosticBuilder<'_>,
@@ -514,24 +514,20 @@ fn add_type_neq_err_label(
                 .lookup_op_method(fn_sig.output(), &[other_ty], Op::Binary(op, is_assign))
                 .is_ok()
             {
-                let (variable_snippet, applicability) = if !fn_sig.inputs().is_empty() {
-                    (
-                        format!("{}( /* arguments */ )", source_map.span_to_snippet(span).unwrap()),
-                        Applicability::HasPlaceholders,
-                    )
-                } else {
-                    (
-                        format!("{}()", source_map.span_to_snippet(span).unwrap()),
-                        Applicability::MaybeIncorrect,
-                    )
-                };
+                if let Ok(snippet) = source_map.span_to_snippet(span) {
+                    let (variable_snippet, applicability) = if !fn_sig.inputs().is_empty() {
+                        (format!("{}( /* arguments */ )", snippet), Applicability::HasPlaceholders)
+                    } else {
+                        (format!("{}()", snippet), Applicability::MaybeIncorrect)
+                    };
 
-                err.span_suggestion(
-                    span,
-                    "you might have forgotten to call this function",
-                    variable_snippet,
-                    applicability,
-                );
+                    err.span_suggestion(
+                        span,
+                        "you might have forgotten to call this function",
+                        variable_snippet,
+                        applicability,
+                    );
+                }
                 return true;
             }
         }

src/test/ui/issues/issue-70724-add_type_neq_err_label-unwrap.rs

@@ -0,0 +1,10 @@
+fn a() -> i32 {
+    3
+}
+
+pub fn main() {
+    assert_eq!(a, 0);
+    //~^ ERROR binary operation `==` cannot
+    //~| ERROR mismatched types
+    //~| ERROR doesn't implement
+}

src/test/ui/issues/issue-70724-add_type_neq_err_label-unwrap.stderr

@@ -0,0 +1,41 @@
+error[E0369]: binary operation `==` cannot be applied to type `fn() -> i32 {a}`
+  --> $DIR/issue-70724-add_type_neq_err_label-unwrap.rs:6:5
+   |
+LL |     assert_eq!(a, 0);
+   |     ^^^^^^^^^^^^^^^^^
+   |     |
+   |     fn() -> i32 {a}
+   |     {integer}
+   |     help: you might have forgotten to call this function: `*left_val()`
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> $DIR/issue-70724-add_type_neq_err_label-unwrap.rs:6:5
+   |
+LL |     assert_eq!(a, 0);
+   |     ^^^^^^^^^^^^^^^^^ expected fn item, found integer
+   |
+   = note: expected fn item `fn() -> i32 {a}`
+                 found type `i32`
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0277]: `fn() -> i32 {a}` doesn't implement `std::fmt::Debug`
+  --> $DIR/issue-70724-add_type_neq_err_label-unwrap.rs:6:5
+   |
+LL | fn a() -> i32 {
+   |    - consider calling this function
+...
+LL |     assert_eq!(a, 0);
+   |     ^^^^^^^^^^^^^^^^^ `fn() -> i32 {a}` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
+   |
+   = help: the trait `std::fmt::Debug` is not implemented for `fn() -> i32 {a}`
+   = help: use parentheses to call the function: `a()`
+   = note: required because of the requirements on the impl of `std::fmt::Debug` for `&fn() -> i32 {a}`
+   = note: required by `std::fmt::Debug::fmt`
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0277, E0308, E0369.
+For more information about an error, try `rustc --explain E0277`.