Add approximate suggestions for rustfix

src/librustc/session/config.rs

@@ -1288,6 +1288,8 @@ 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"),
+    approximate_suggestions: 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:

src/librustc/session/mod.rs

@@ -910,10 +910,12 @@ pub fn build_session_with_codemap(sopts: config::Options,
             Box::new(EmitterWriter::new(dst, Some(codemap.clone()), false))
         }
         (config::ErrorOutputType::Json(pretty), None) => {
-            Box::new(JsonEmitter::stderr(Some(registry), codemap.clone(), pretty))
+            Box::new(JsonEmitter::stderr(Some(registry), codemap.clone(),
+                     pretty, sopts.debugging_opts.approximate_suggestions))
         }
         (config::ErrorOutputType::Json(pretty), Some(dst)) => {
-            Box::new(JsonEmitter::new(dst, Some(registry), codemap.clone(), pretty))
+            Box::new(JsonEmitter::new(dst, Some(registry), codemap.clone(),
+                     pretty, sopts.debugging_opts.approximate_suggestions))
         }
         (config::ErrorOutputType::Short(color_config), None) => {
             Box::new(EmitterWriter::stderr(color_config, Some(codemap.clone()), true))

src/librustc_errors/diagnostic.rs

@@ -222,6 +222,7 @@ impl Diagnostic {
             }],
             msg: msg.to_owned(),
             show_code_when_inline: false,
+            approximate: false,
         });
         self
     }
@@ -252,6 +253,7 @@ impl Diagnostic {
             }],
             msg: msg.to_owned(),
             show_code_when_inline: true,
+            approximate: false,
         });
         self
     }
@@ -267,6 +269,41 @@ impl Diagnostic {
             }).collect(),
             msg: msg.to_owned(),
             show_code_when_inline: true,
+            approximate: false,
+        });
+        self
+    }
+
+    /// This is a suggestion that may contain mistakes or fillers and should
+    /// be read and understood by a human.
+    pub fn span_approximate_suggestion(&mut self, sp: Span, msg: &str,
+                                       suggestion: String) -> &mut Self {
+        self.suggestions.push(CodeSuggestion {
+            substitutions: vec![Substitution {
+                parts: vec![SubstitutionPart {
+                    snippet: suggestion,
+                    span: sp,
+                }],
+            }],
+            msg: msg.to_owned(),
+            show_code_when_inline: true,
+            approximate: true,
+        });
+        self
+    }
+
+    pub fn span_approximate_suggestions(&mut self, sp: Span, msg: &str,
+                                        suggestions: Vec<String>) -> &mut Self {
+        self.suggestions.push(CodeSuggestion {
+            substitutions: suggestions.into_iter().map(|snippet| Substitution {
+                parts: vec![SubstitutionPart {
+                    snippet,
+                    span: sp,
+                }],
+            }).collect(),
+            msg: msg.to_owned(),
+            show_code_when_inline: true,
+            approximate: true,
         });
         self
     }

src/librustc_errors/diagnostic_builder.rs

@@ -186,6 +186,16 @@ impl<'a> DiagnosticBuilder<'a> {
                                      msg: &str,
                                      suggestions: Vec<String>)
                                      -> &mut Self);
+    forward!(pub fn span_approximate_suggestion(&mut self,
+                                                sp: Span,
+                                                msg: &str,
+                                                suggestion: String)
+                                                -> &mut Self);
+    forward!(pub fn span_approximate_suggestions(&mut self,
+                                                 sp: Span,
+                                                 msg: &str,
+                                                 suggestions: Vec<String>)
+                                                 -> &mut Self);
     forward!(pub fn set_span<S: Into<MultiSpan>>(&mut self, sp: S) -> &mut Self);
     forward!(pub fn code(&mut self, s: DiagnosticId) -> &mut Self);
 

src/librustc_errors/lib.rs

@@ -83,6 +83,12 @@ pub struct CodeSuggestion {
     pub substitutions: Vec<Substitution>,
     pub msg: String,
     pub show_code_when_inline: bool,
+    /// Whether or not the suggestion is approximate
+    ///
+    /// Sometimes we may show suggestions with placeholders,
+    /// which are useful for users but not useful for
+    /// tools like rustfix
+    pub approximate: bool,
 }
 
 #[derive(Clone, Debug, PartialEq, Hash, RustcEncodable, RustcDecodable)]

src/libsyntax/feature_gate.rs

@@ -788,6 +788,11 @@ 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 \

src/libsyntax/json.rs

@@ -38,34 +38,41 @@ pub struct JsonEmitter {
     registry: Option<Registry>,
     cm: Rc<CodeMapper + 'static>,
     pretty: bool,
+    /// Whether "approximate suggestions" are enabled in the config
+    approximate_suggestions: bool,
 }
 
 impl JsonEmitter {
     pub fn stderr(registry: Option<Registry>,
                   code_map: Rc<CodeMap>,
-                  pretty: bool) -> JsonEmitter {
+                  pretty: bool,
+                  approximate_suggestions: bool) -> JsonEmitter {
         JsonEmitter {
             dst: Box::new(io::stderr()),
             registry,
             cm: code_map,
             pretty,
+            approximate_suggestions,
         }
     }
 
     pub fn basic(pretty: bool) -> JsonEmitter {
         let file_path_mapping = FilePathMapping::empty();
-        JsonEmitter::stderr(None, Rc::new(CodeMap::new(file_path_mapping)), pretty)
+        JsonEmitter::stderr(None, Rc::new(CodeMap::new(file_path_mapping)),
+                            pretty, false)
     }
 
     pub fn new(dst: Box<Write + Send>,
                registry: Option<Registry>,
                code_map: Rc<CodeMap>,
-               pretty: bool) -> JsonEmitter {
+               pretty: bool,
+               approximate_suggestions: bool) -> JsonEmitter {
         JsonEmitter {
             dst,
             registry,
             cm: code_map,
             pretty,
+            approximate_suggestions,
         }
     }
 }
@@ -101,6 +108,7 @@ struct Diagnostic {
 }
 
 #[derive(RustcEncodable)]
+#[allow(unused_attributes)]
 struct DiagnosticSpan {
     file_name: String,
     byte_start: u32,
@@ -121,6 +129,9 @@ struct DiagnosticSpan {
     /// If we are suggesting a replacement, this will contain text
     /// that should be sliced in atop this span.
     suggested_replacement: Option<String>,
+    /// If the suggestion is approximate
+    #[rustc_serialize_exclude_null]
+    suggestion_approximate: Option<bool>,
     /// Macro invocations that created the code at this span, if any.
     expansion: Option<Box<DiagnosticSpanMacroExpansion>>,
 }
@@ -220,7 +231,7 @@ impl Diagnostic {
 
 impl DiagnosticSpan {
     fn from_span_label(span: SpanLabel,
-                       suggestion: Option<&String>,
+                       suggestion: Option<(&String, bool)>,
                        je: &JsonEmitter)
                        -> DiagnosticSpan {
         Self::from_span_etc(span.span,
@@ -233,7 +244,7 @@ impl DiagnosticSpan {
     fn from_span_etc(span: Span,
                      is_primary: bool,
                      label: Option<String>,
-                     suggestion: Option<&String>,
+                     suggestion: Option<(&String, bool)>,
                      je: &JsonEmitter)
                      -> DiagnosticSpan {
         // obtain the full backtrace from the `macro_backtrace`
@@ -253,7 +264,7 @@ impl DiagnosticSpan {
     fn from_span_full(span: Span,
                       is_primary: bool,
                       label: Option<String>,
-                      suggestion: Option<&String>,
+                      suggestion: Option<(&String, bool)>,
                       mut backtrace: vec::IntoIter<MacroBacktrace>,
                       je: &JsonEmitter)
                       -> DiagnosticSpan {
@@ -281,6 +292,13 @@ impl DiagnosticSpan {
                 def_site_span,
             })
         });
+
+        let suggestion_approximate = if je.approximate_suggestions {
+             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,
@@ -291,7 +309,8 @@ impl DiagnosticSpan {
             column_end: end.col.0 + 1,
             is_primary,
             text: DiagnosticSpanLine::from_span(span, je),
-            suggested_replacement: suggestion.cloned(),
+            suggested_replacement: suggestion.map(|x| x.0.clone()),
+            suggestion_approximate,
             expansion: backtrace_step,
             label,
         }
@@ -309,14 +328,15 @@ impl DiagnosticSpan {
         suggestion.substitutions
                       .iter()
                       .flat_map(|substitution| {
-                          substitution.parts.iter().map(move |suggestion| {
+                          substitution.parts.iter().map(move |suggestion_inner| {
                               let span_label = SpanLabel {
-                                  span: suggestion.span,
+                                  span: suggestion_inner.span,
                                   is_primary: true,
                                   label: None,
                               };
                               DiagnosticSpan::from_span_label(span_label,
-                                                              Some(&suggestion.snippet),
+                                                              Some((&suggestion_inner.snippet,
+                                                                   suggestion.approximate)),
                                                               je)
                           })
                       })

src/libsyntax/lib.rs

@@ -25,6 +25,7 @@
 #![feature(match_default_bindings)]
 #![feature(i128_type)]
 #![feature(const_atomic_usize_new)]
+#![feature(rustc_attrs)]
 
 // See librustc_cratesio_shim/Cargo.toml for a comment explaining this.
 #[allow(unused_extern_crates)]

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, .. }) in fields.iter().enumerate() {
+            for (i, &FieldInfo { name, ref self_, span, attrs, .. }) in fields.iter().enumerate() {
                 let name = match name {
                     Some(id) => id.name,
                     None => Symbol::intern(&format!("_field{}", i)),
@@ -212,7 +212,19 @@ fn encodable_substructure(cx: &mut ExtCtxt,
                 } else {
                     cx.expr(span, ExprKind::Ret(Some(call)))
                 };
-                stmts.push(cx.stmt_expr(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);
+                stmts.push(stmt);
             }
 
             // unit structs have no fields and need to return Ok()