simplify how the hir_typeck_pass_to_variadic_function diagnostic is created

compiler/rustc_hir_typeck/messages.ftl

@@ -146,7 +146,6 @@ hir_typeck_option_result_copied = use `{$def_path}::copied` to copy the value in
 
 hir_typeck_pass_to_variadic_function = can't pass `{$ty}` to variadic function
     .suggestion = cast the value to `{$cast_ty}`
-    .help = cast the value to `{$cast_ty}`
     .teach_help = certain types, like `{$ty}`, must be casted before passing them to a variadic function, because of arcane ABI rules dictated by the C standard
 
 hir_typeck_ptr_cast_add_auto_to_object = adding {$traits_len ->

compiler/rustc_hir_typeck/src/errors.rs

@@ -789,11 +789,8 @@ pub(crate) struct PassToVariadicFunction<'a, 'tcx> {
     pub span: Span,
     pub ty: Ty<'tcx>,
     pub cast_ty: &'a str,
-    #[suggestion(code = "{replace}", applicability = "machine-applicable")]
+    #[suggestion(code = " as {cast_ty}", applicability = "machine-applicable", style = "verbose")]
-    pub sugg_span: Option<Span>,
+    pub sugg_span: Span,
-    pub replace: String,
-    #[help]
-    pub help: bool,
     #[note(hir_typeck_teach_help)]
     pub(crate) teach: bool,
 }

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -440,20 +440,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     ty: Ty<'tcx>,
                     cast_ty: &str,
                 ) {
-                    let (sugg_span, replace, help) =
-                        if let Ok(snippet) = sess.source_map().span_to_snippet(span) {
-                            (Some(span), format!("{snippet} as {cast_ty}"), false)
-                        } else {
-                            (None, "".to_string(), true)
-                        };
-
                     sess.dcx().emit_err(errors::PassToVariadicFunction {
                         span,
                         ty,
                         cast_ty,
-                        help,
+                        sugg_span: span.shrink_to_hi(),
-                        replace,
-                        sugg_span,
                         teach: sess.teach(E0617),
                     });
                 }

tests/ui/c-variadic/variadic-ffi-1.stderr

@@ -62,37 +62,67 @@ error[E0617]: can't pass `f32` to variadic function
   --> $DIR/variadic-ffi-1.rs:28:19
    |
 LL |         foo(1, 2, 3f32);
-   |                   ^^^^ help: cast the value to `c_double`: `3f32 as c_double`
+   |                   ^^^^
+   |
+help: cast the value to `c_double`
+   |
+LL |         foo(1, 2, 3f32 as c_double);
+   |                        +++++++++++
 
 error[E0617]: can't pass `bool` to variadic function
   --> $DIR/variadic-ffi-1.rs:29:19
    |
 LL |         foo(1, 2, true);
-   |                   ^^^^ help: cast the value to `c_int`: `true as c_int`
+   |                   ^^^^
+   |
+help: cast the value to `c_int`
+   |
+LL |         foo(1, 2, true as c_int);
+   |                        ++++++++
 
 error[E0617]: can't pass `i8` to variadic function
   --> $DIR/variadic-ffi-1.rs:30:19
    |
 LL |         foo(1, 2, 1i8);
-   |                   ^^^ help: cast the value to `c_int`: `1i8 as c_int`
+   |                   ^^^
+   |
+help: cast the value to `c_int`
+   |
+LL |         foo(1, 2, 1i8 as c_int);
+   |                       ++++++++
 
 error[E0617]: can't pass `u8` to variadic function
   --> $DIR/variadic-ffi-1.rs:31:19
    |
 LL |         foo(1, 2, 1u8);
-   |                   ^^^ help: cast the value to `c_uint`: `1u8 as c_uint`
+   |                   ^^^
+   |
+help: cast the value to `c_uint`
+   |
+LL |         foo(1, 2, 1u8 as c_uint);
+   |                       +++++++++
 
 error[E0617]: can't pass `i16` to variadic function
   --> $DIR/variadic-ffi-1.rs:32:19
    |
 LL |         foo(1, 2, 1i16);
-   |                   ^^^^ help: cast the value to `c_int`: `1i16 as c_int`
+   |                   ^^^^
+   |
+help: cast the value to `c_int`
+   |
+LL |         foo(1, 2, 1i16 as c_int);
+   |                        ++++++++
 
 error[E0617]: can't pass `u16` to variadic function
   --> $DIR/variadic-ffi-1.rs:33:19
    |
 LL |         foo(1, 2, 1u16);
-   |                   ^^^^ help: cast the value to `c_uint`: `1u16 as c_uint`
+   |                   ^^^^
+   |
+help: cast the value to `c_uint`
+   |
+LL |         foo(1, 2, 1u16 as c_uint);
+   |                        +++++++++
 
 error: aborting due to 11 previous errors
 

tests/ui/error-codes/E0617.stderr

@@ -2,31 +2,56 @@ error[E0617]: can't pass `f32` to variadic function
   --> $DIR/E0617.rs:7:36
    |
 LL |         printf(::std::ptr::null(), 0f32);
-   |                                    ^^^^ help: cast the value to `c_double`: `0f32 as c_double`
+   |                                    ^^^^
+   |
+help: cast the value to `c_double`
+   |
+LL |         printf(::std::ptr::null(), 0f32 as c_double);
+   |                                         +++++++++++
 
 error[E0617]: can't pass `i8` to variadic function
   --> $DIR/E0617.rs:10:36
    |
 LL |         printf(::std::ptr::null(), 0i8);
-   |                                    ^^^ help: cast the value to `c_int`: `0i8 as c_int`
+   |                                    ^^^
+   |
+help: cast the value to `c_int`
+   |
+LL |         printf(::std::ptr::null(), 0i8 as c_int);
+   |                                        ++++++++
 
 error[E0617]: can't pass `i16` to variadic function
   --> $DIR/E0617.rs:13:36
    |
 LL |         printf(::std::ptr::null(), 0i16);
-   |                                    ^^^^ help: cast the value to `c_int`: `0i16 as c_int`
+   |                                    ^^^^
+   |
+help: cast the value to `c_int`
+   |
+LL |         printf(::std::ptr::null(), 0i16 as c_int);
+   |                                         ++++++++
 
 error[E0617]: can't pass `u8` to variadic function
   --> $DIR/E0617.rs:16:36
    |
 LL |         printf(::std::ptr::null(), 0u8);
-   |                                    ^^^ help: cast the value to `c_uint`: `0u8 as c_uint`
+   |                                    ^^^
+   |
+help: cast the value to `c_uint`
+   |
+LL |         printf(::std::ptr::null(), 0u8 as c_uint);
+   |                                        +++++++++
 
 error[E0617]: can't pass `u16` to variadic function
   --> $DIR/E0617.rs:19:36
    |
 LL |         printf(::std::ptr::null(), 0u16);
-   |                                    ^^^^ help: cast the value to `c_uint`: `0u16 as c_uint`
+   |                                    ^^^^
+   |
+help: cast the value to `c_uint`
+   |
+LL |         printf(::std::ptr::null(), 0u16 as c_uint);
+   |                                         +++++++++
 
 error[E0617]: can't pass a function item to a variadic function
   --> $DIR/E0617.rs:22:36