Avoid suggesting literal formatting that turns into member access

Fixes #90974

Author: notriddle

compiler/rustc_typeck/src/check/method/suggest.rs

@@ -317,14 +317,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                     .span_to_snippet(lit.span)
                                     .unwrap_or_else(|_| "<numeric literal>".to_owned());
 
+                                // If this is a floating point literal that ends with '.',
+                                // get rid of it to stop this from becoming a member access.
+                                let snippet = snippet.strip_suffix('.').unwrap_or(&snippet);
+
                                 err.span_suggestion(
                                     lit.span,
                                     &format!(
                                         "you must specify a concrete type for this numeric value, \
                                          like `{}`",
                                         concrete_type
                                     ),
-                                    format!("{}_{}", snippet, concrete_type),
+                                    format!("{snippet}_{concrete_type}"),
                                     Applicability::MaybeIncorrect,
                                 );
                             }

src/test/ui/suggestions/issue-90974.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("{}", (3.).recip()); //~ERROR
+}

src/test/ui/suggestions/issue-90974.stderr

@@ -0,0 +1,14 @@
+error[E0689]: can't call method `recip` on ambiguous numeric type `{float}`
+  --> $DIR/issue-90974.rs:2:25
+   |
+LL |     println!("{}", (3.).recip());
+   |                         ^^^^^
+   |
+help: you must specify a concrete type for this numeric value, like `f32`
+   |
+LL |     println!("{}", (3_f32).recip());
+   |                     ~~~~~
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0689`.