diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index e0c0fdd2a01fe..960bbfdd1ef71 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -1316,8 +1316,6 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
     dep_info_omit_d_target: bool = (false, parse_bool, [TRACKED],
         "in dep-info output, omit targets for tracking dependencies of the dep-info files \
          themselves"),
-    suggestion_applicability: bool = (false, parse_bool, [UNTRACKED],
-        "include machine-applicability of suggestions in JSON output"),
     unpretty: Option<String> = (None, parse_unpretty, [UNTRACKED],
         "Present the input source, unstable (and less-pretty) variants;
         valid types are any of the types for `--pretty`, as well as:
diff --git a/src/librustc/session/mod.rs b/src/librustc/session/mod.rs
index 6c8d4f5669e8e..8df66d8d68855 100644
--- a/src/librustc/session/mod.rs
+++ b/src/librustc/session/mod.rs
@@ -1018,7 +1018,6 @@ pub fn build_session_with_codemap(
                     Some(registry),
                     codemap.clone(),
                     pretty,
-                    sopts.debugging_opts.suggestion_applicability,
                 ).ui_testing(sopts.debugging_opts.ui_testing),
             ),
             (config::ErrorOutputType::Json(pretty), Some(dst)) => Box::new(
@@ -1027,7 +1026,6 @@ pub fn build_session_with_codemap(
                     Some(registry),
                     codemap.clone(),
                     pretty,
-                    sopts.debugging_opts.suggestion_applicability,
                 ).ui_testing(sopts.debugging_opts.ui_testing),
             ),
             (config::ErrorOutputType::Short(color_config), None) => Box::new(
diff --git a/src/librustdoc/core.rs b/src/librustdoc/core.rs
index 90889890e0bc2..458ed105d2650 100644
--- a/src/librustdoc/core.rs
+++ b/src/librustdoc/core.rs
@@ -144,7 +144,6 @@ pub fn new_handler(error_format: ErrorOutputType, codemap: Option<Lrc<codemap::C
                     None,
                     codemap,
                     pretty,
-                    sessopts.debugging_opts.suggestion_applicability,
                 ).ui_testing(sessopts.debugging_opts.ui_testing)
             )
         },
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 604df862dc25b..709c3653b0267 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -846,11 +846,6 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
                                                        is just used for rustc unit tests \
                                                        and will never be stable",
                                                       cfg_fn!(rustc_attrs))),
-    ("rustc_serialize_exclude_null", Normal, Gated(Stability::Unstable,
-                                             "rustc_attrs",
-                                             "the `#[rustc_serialize_exclude_null]` attribute \
-                                              is an internal-only feature",
-                                             cfg_fn!(rustc_attrs))),
     ("rustc_synthetic", Whitelisted, Gated(Stability::Unstable,
                                                       "rustc_attrs",
                                                       "this attribute \
diff --git a/src/libsyntax/json.rs b/src/libsyntax/json.rs
index 2f15e75093b10..f129aea32b8fe 100644
--- a/src/libsyntax/json.rs
+++ b/src/libsyntax/json.rs
@@ -38,22 +38,18 @@ pub struct JsonEmitter {
     registry: Option<Registry>,
     cm: Lrc<CodeMapper + sync::Send + sync::Sync>,
     pretty: bool,
-    /// Whether "approximate suggestions" are enabled in the config
-    suggestion_applicability: bool,
     ui_testing: bool,
 }
 
 impl JsonEmitter {
     pub fn stderr(registry: Option<Registry>,
                   code_map: Lrc<CodeMap>,
-                  pretty: bool,
-                  suggestion_applicability: bool) -> JsonEmitter {
+                  pretty: bool) -> JsonEmitter {
         JsonEmitter {
             dst: Box::new(io::stderr()),
             registry,
             cm: code_map,
             pretty,
-            suggestion_applicability,
             ui_testing: false,
         }
     }
@@ -61,20 +57,18 @@ impl JsonEmitter {
     pub fn basic(pretty: bool) -> JsonEmitter {
         let file_path_mapping = FilePathMapping::empty();
         JsonEmitter::stderr(None, Lrc::new(CodeMap::new(file_path_mapping)),
-                            pretty, false)
+                            pretty)
     }
 
     pub fn new(dst: Box<Write + Send>,
                registry: Option<Registry>,
                code_map: Lrc<CodeMap>,
-               pretty: bool,
-               suggestion_applicability: bool) -> JsonEmitter {
+               pretty: bool) -> JsonEmitter {
         JsonEmitter {
             dst,
             registry,
             cm: code_map,
             pretty,
-            suggestion_applicability,
             ui_testing: false,
         }
     }
@@ -137,7 +131,6 @@ struct DiagnosticSpan {
     /// that should be sliced in atop this span.
     suggested_replacement: Option<String>,
     /// If the suggestion is approximate
-    #[rustc_serialize_exclude_null]
     suggestion_applicability: Option<Applicability>,
     /// Macro invocations that created the code at this span, if any.
     expansion: Option<Box<DiagnosticSpanMacroExpansion>>,
@@ -301,12 +294,6 @@ impl DiagnosticSpan {
             })
         });
 
-        let suggestion_applicability = if je.suggestion_applicability {
-             suggestion.map(|x| x.1)
-        } else {
-            None
-        };
-
         DiagnosticSpan {
             file_name: start.file.name.to_string(),
             byte_start: span.lo().0 - start.file.start_pos.0,
@@ -318,7 +305,7 @@ impl DiagnosticSpan {
             is_primary,
             text: DiagnosticSpanLine::from_span(span, je),
             suggested_replacement: suggestion.map(|x| x.0.clone()),
-            suggestion_applicability,
+            suggestion_applicability: suggestion.map(|x| x.1),
             expansion: backtrace_step,
             label,
         }
diff --git a/src/libsyntax_ext/deriving/encodable.rs b/src/libsyntax_ext/deriving/encodable.rs
index 2c6c18cc51cd7..8b409df1f0996 100644
--- a/src/libsyntax_ext/deriving/encodable.rs
+++ b/src/libsyntax_ext/deriving/encodable.rs
@@ -190,7 +190,7 @@ fn encodable_substructure(cx: &mut ExtCtxt,
         Struct(_, ref fields) => {
             let emit_struct_field = cx.ident_of("emit_struct_field");
             let mut stmts = Vec::new();
-            for (i, &FieldInfo { name, ref self_, span, attrs, .. }) in fields.iter().enumerate() {
+            for (i, &FieldInfo { name, ref self_, span, .. }) in fields.iter().enumerate() {
                 let name = match name {
                     Some(id) => id.name,
                     None => Symbol::intern(&format!("_field{}", i)),
@@ -213,17 +213,7 @@ fn encodable_substructure(cx: &mut ExtCtxt,
                     cx.expr(span, ExprKind::Ret(Some(call)))
                 };
 
-                // This exists for https://github.com/rust-lang/rust/pull/47540
-                //
-                // If we decide to stabilize that flag this can be removed
-                let expr = if attrs.iter().any(|a| a.check_name("rustc_serialize_exclude_null")) {
-                    let is_some = cx.ident_of("is_some");
-                    let condition = cx.expr_method_call(span, self_.clone(), is_some, vec![]);
-                    cx.expr_if(span, condition, call, None)
-                } else {
-                    call
-                };
-                let stmt = cx.stmt_expr(expr);
+                let stmt = cx.stmt_expr(call);
                 stmts.push(stmt);
             }
 
diff --git a/src/test/ui/lint/unused_parens_json_suggestion.stderr b/src/test/ui/lint/unused_parens_json_suggestion.stderr
index 40d3758ded5c6..2ec0111ff4b66 100644
--- a/src/test/ui/lint/unused_parens_json_suggestion.stderr
+++ b/src/test/ui/lint/unused_parens_json_suggestion.stderr
@@ -24,6 +24,7 @@
       ],
       "label": null,
       "suggested_replacement": null,
+      "suggestion_applicability": null,
       "expansion": null
     }
   ],
@@ -51,6 +52,7 @@
           ],
           "label": null,
           "suggested_replacement": null,
+          "suggestion_applicability": null,
           "expansion": null
         }
       ],
@@ -80,6 +82,7 @@
           ],
           "label": null,
           "suggested_replacement": "1 / (2 + 3)",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         }
       ],
diff --git a/src/test/ui/lint/use_suggestion_json.stderr b/src/test/ui/lint/use_suggestion_json.stderr
index b90c5aa3a4bac..ce2657a44953b 100644
--- a/src/test/ui/lint/use_suggestion_json.stderr
+++ b/src/test/ui/lint/use_suggestion_json.stderr
@@ -89,6 +89,7 @@ mod foo {
       ],
       "label": "not found in this scope",
       "suggested_replacement": null,
+      "suggestion_applicability": null,
       "expansion": null
     }
   ],
@@ -118,6 +119,7 @@ mod foo {
           "suggested_replacement": "use std::collections::binary_heap::Iter;
 
 ",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         },
         {
@@ -140,6 +142,7 @@ mod foo {
           "suggested_replacement": "use std::collections::btree_map::Iter;
 
 ",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         },
         {
@@ -162,6 +165,7 @@ mod foo {
           "suggested_replacement": "use std::collections::btree_set::Iter;
 
 ",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         },
         {
@@ -184,6 +188,7 @@ mod foo {
           "suggested_replacement": "use std::collections::hash_map::Iter;
 
 ",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         },
         {
@@ -206,6 +211,7 @@ mod foo {
           "suggested_replacement": "use std::collections::hash_set::Iter;
 
 ",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         },
         {
@@ -228,6 +234,7 @@ mod foo {
           "suggested_replacement": "use std::collections::linked_list::Iter;
 
 ",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         },
         {
@@ -250,6 +257,7 @@ mod foo {
           "suggested_replacement": "use std::collections::vec_deque::Iter;
 
 ",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         },
         {
@@ -272,6 +280,7 @@ mod foo {
           "suggested_replacement": "use std::option::Iter;
 
 ",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         },
         {
@@ -294,6 +303,7 @@ mod foo {
           "suggested_replacement": "use std::path::Iter;
 
 ",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         },
         {
@@ -316,6 +326,7 @@ mod foo {
           "suggested_replacement": "use std::result::Iter;
 
 ",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         },
         {
@@ -338,6 +349,7 @@ mod foo {
           "suggested_replacement": "use std::slice::Iter;
 
 ",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         },
         {
@@ -360,6 +372,7 @@ mod foo {
           "suggested_replacement": "use std::sync::mpsc::Iter;
 
 ",
+          "suggestion_applicability": "Unspecified",
           "expansion": null
         }
       ],