Remove --extern-location and all associated code

`--extern-location` was an experiment to investigate the best way to
generate useful diagnostics for unused dependency warnings by enabling a
build system to identify the corresponding build config.

While I did successfully use this, I've since been convinced the
alternative `--json unused-externs` mechanism is the way to go, and
there's no point in having two mechanisms with basically the same
functionality.

This effectively reverts rust-lang#72603

Author: jsgf

Cargo.lock

@@ -3924,7 +3924,6 @@ dependencies = [
  "rustc_infer",
  "rustc_middle",
  "rustc_parse_format",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",

compiler/rustc_errors/src/diagnostic.rs

@@ -1,12 +1,11 @@
 use crate::snippet::Style;
 use crate::{
     CodeSuggestion, DiagnosticMessage, Level, MultiSpan, Substitution, SubstitutionPart,
-    SuggestionStyle, ToolMetadata,
+    SuggestionStyle,
 };
 use rustc_data_structures::stable_map::FxHashMap;
 use rustc_error_messages::FluentValue;
 use rustc_lint_defs::{Applicability, LintExpectationId};
-use rustc_serialize::json::Json;
 use rustc_span::edition::LATEST_STABLE_EDITION;
 use rustc_span::symbol::{Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
@@ -554,7 +553,6 @@ impl Diagnostic {
             msg: msg.into(),
             style,
             applicability,
-            tool_metadata: Default::default(),
         });
         self
     }
@@ -582,7 +580,6 @@ impl Diagnostic {
             msg: msg.into(),
             style: SuggestionStyle::CompletelyHidden,
             applicability,
-            tool_metadata: Default::default(),
         });
         self
     }
@@ -637,7 +634,6 @@ impl Diagnostic {
             msg: msg.into(),
             style,
             applicability,
-            tool_metadata: Default::default(),
         });
         self
     }
@@ -680,7 +676,6 @@ impl Diagnostic {
             msg: msg.into(),
             style: SuggestionStyle::ShowCode,
             applicability,
-            tool_metadata: Default::default(),
         });
         self
     }
@@ -705,7 +700,6 @@ impl Diagnostic {
             msg: msg.into(),
             style: SuggestionStyle::ShowCode,
             applicability,
-            tool_metadata: Default::default(),
         });
         self
     }
@@ -774,23 +768,6 @@ impl Diagnostic {
         self
     }
 
-    /// Adds a suggestion intended only for a tool. The intent is that the metadata encodes
-    /// the suggestion in a tool-specific way, as it may not even directly involve Rust code.
-    pub fn tool_only_suggestion_with_metadata(
-        &mut self,
-        msg: impl Into<DiagnosticMessage>,
-        applicability: Applicability,
-        tool_metadata: Json,
-    ) {
-        self.push_suggestion(CodeSuggestion {
-            substitutions: vec![],
-            msg: msg.into(),
-            style: SuggestionStyle::CompletelyHidden,
-            applicability,
-            tool_metadata: ToolMetadata::new(tool_metadata),
-        })
-    }
-
     pub fn set_span<S: Into<MultiSpan>>(&mut self, sp: S) -> &mut Self {
         self.span = sp.into();
         if let Some(span) = self.span.primary_span() {

compiler/rustc_errors/src/json.rs

@@ -14,7 +14,6 @@ use rustc_span::source_map::{FilePathMapping, SourceMap};
 use crate::emitter::{Emitter, HumanReadableErrorType};
 use crate::registry::Registry;
 use crate::DiagnosticId;
-use crate::ToolMetadata;
 use crate::{
     CodeSuggestion, FluentBundle, LazyFallbackBundle, MultiSpan, SpanLabel, SubDiagnostic,
 };
@@ -30,7 +29,6 @@ use std::sync::{Arc, Mutex};
 use std::vec;
 
 use rustc_serialize::json::{as_json, as_pretty_json};
-use rustc_serialize::{Encodable, Encoder};
 
 #[cfg(test)]
 mod tests;
@@ -205,8 +203,7 @@ impl Emitter for JsonEmitter {
 
 // The following data types are provided just for serialisation.
 
-// NOTE: this has a manual implementation of Encodable which needs to be updated in
-// parallel.
+#[derive(Encodable)]
 struct Diagnostic {
     /// The primary error message.
     message: String,
@@ -218,65 +215,6 @@ struct Diagnostic {
     children: Vec<Diagnostic>,
     /// The message as rustc would render it.
     rendered: Option<String>,
-    /// Extra tool metadata
-    tool_metadata: ToolMetadata,
-}
-
-macro_rules! encode_fields {
-    (
-        $enc:expr,                  // encoder
-        $idx:expr,                  // starting field index
-        $struct:expr,               // struct we're serializing
-        $struct_name:ident,         // struct name
-        [ $($name:ident),+$(,)? ],  // fields to encode
-        [ $($ignore:ident),+$(,)? ] // fields we're skipping
-    ) => {
-        {
-            // Pattern match to make sure all fields are accounted for
-            let $struct_name { $($name,)+ $($ignore: _,)+ } = $struct;
-            let mut idx = $idx;
-            $(
-                $enc.emit_struct_field(
-                    stringify!($name),
-                    idx == 0,
-                    |enc| $name.encode(enc),
-                )?;
-                idx += 1;
-            )+
-            idx
-        }
-    };
-}
-
-// Special-case encoder to skip tool_metadata if not set
-impl<E: Encoder> Encodable<E> for Diagnostic {
-    fn encode(&self, s: &mut E) -> Result<(), E::Error> {
-        s.emit_struct(false, |s| {
-            let mut idx = 0;
-
-            idx = encode_fields!(
-                s,
-                idx,
-                self,
-                Self,
-                [message, code, level, spans, children, rendered],
-                [tool_metadata]
-            );
-            if self.tool_metadata.is_set() {
-                idx = encode_fields!(
-                    s,
-                    idx,
-                    self,
-                    Self,
-                    [tool_metadata],
-                    [message, code, level, spans, children, rendered]
-                );
-            }
-
-            let _ = idx;
-            Ok(())
-        })
-    }
 }
 
 #[derive(Encodable)]
@@ -380,7 +318,6 @@ impl Diagnostic {
                 spans: DiagnosticSpan::from_suggestion(sugg, &args, je),
                 children: vec![],
                 rendered: None,
-                tool_metadata: sugg.tool_metadata.clone(),
             }
         });
 
@@ -428,7 +365,6 @@ impl Diagnostic {
                 .chain(sugg)
                 .collect(),
             rendered: Some(output),
-            tool_metadata: ToolMetadata::default(),
         }
     }
 
@@ -449,7 +385,6 @@ impl Diagnostic {
                 .unwrap_or_else(|| DiagnosticSpan::from_multispan(&diag.span, args, je)),
             children: vec![],
             rendered: None,
-            tool_metadata: ToolMetadata::default(),
         }
     }
 }

compiler/rustc_errors/src/lib.rs

@@ -36,13 +36,11 @@ pub use rustc_error_messages::{
     LazyFallbackBundle, MultiSpan, SpanLabel, DEFAULT_LOCALE_RESOURCES,
 };
 pub use rustc_lint_defs::{pluralize, Applicability};
-use rustc_serialize::json::Json;
-use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use rustc_span::source_map::SourceMap;
 use rustc_span::{Loc, Span};
 
 use std::borrow::Cow;
-use std::hash::{Hash, Hasher};
+use std::hash::Hash;
 use std::num::NonZeroUsize;
 use std::panic;
 use std::path::Path;
@@ -93,39 +91,6 @@ impl SuggestionStyle {
     }
 }
 
-#[derive(Clone, Debug, PartialEq, Default)]
-pub struct ToolMetadata(pub Option<Json>);
-
-impl ToolMetadata {
-    fn new(json: Json) -> Self {
-        ToolMetadata(Some(json))
-    }
-
-    fn is_set(&self) -> bool {
-        self.0.is_some()
-    }
-}
-
-impl Hash for ToolMetadata {
-    fn hash<H: Hasher>(&self, _state: &mut H) {}
-}
-
-// Doesn't really need to round-trip
-impl<D: Decoder> Decodable<D> for ToolMetadata {
-    fn decode(_d: &mut D) -> Self {
-        ToolMetadata(None)
-    }
-}
-
-impl<S: Encoder> Encodable<S> for ToolMetadata {
-    fn encode(&self, e: &mut S) -> Result<(), S::Error> {
-        match &self.0 {
-            None => e.emit_unit(),
-            Some(json) => json.encode(e),
-        }
-    }
-}
-
 #[derive(Clone, Debug, PartialEq, Hash, Encodable, Decodable)]
 pub struct CodeSuggestion {
     /// Each substitute can have multiple variants due to multiple
@@ -159,8 +124,6 @@ pub struct CodeSuggestion {
     /// which are useful for users but not useful for
     /// tools like rustfix
     pub applicability: Applicability,
-    /// Tool-specific metadata
-    pub tool_metadata: ToolMetadata,
 }
 
 #[derive(Clone, Debug, PartialEq, Hash, Encodable, Decodable)]

compiler/rustc_lint/Cargo.toml

@@ -18,7 +18,6 @@ rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_feature = { path = "../rustc_feature" }
 rustc_index = { path = "../rustc_index" }
 rustc_session = { path = "../rustc_session" }
-rustc_serialize = { path = "../rustc_serialize" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }
 rustc_parse_format = { path = "../rustc_parse_format" }
 rustc_infer = { path = "../rustc_infer" }

compiler/rustc_lint/src/context.rs

@@ -32,8 +32,7 @@ use rustc_middle::middle::stability;
 use rustc_middle::ty::layout::{LayoutError, LayoutOfHelpers, TyAndLayout};
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, print::Printer, subst::GenericArg, RegisteredTools, Ty, TyCtxt};
-use rustc_serialize::json::Json;
-use rustc_session::lint::{BuiltinLintDiagnostics, ExternDepSpec};
+use rustc_session::lint::BuiltinLintDiagnostics;
 use rustc_session::lint::{FutureIncompatibleInfo, Level, Lint, LintBuffer, LintId};
 use rustc_session::Session;
 use rustc_span::lev_distance::find_best_match_for_name;
@@ -712,30 +711,6 @@ pub trait LintContext: Sized {
                 BuiltinLintDiagnostics::LegacyDeriveHelpers(span) => {
                     db.span_label(span, "the attribute is introduced here");
                 }
-                BuiltinLintDiagnostics::ExternDepSpec(krate, loc) => {
-                    let json = match loc {
-                        ExternDepSpec::Json(json) => {
-                            db.help(&format!("remove unnecessary dependency `{}`", krate));
-                            json
-                        }
-                        ExternDepSpec::Raw(raw) => {
-                            db.help(&format!("remove unnecessary dependency `{}` at `{}`", krate, raw));
-                            db.span_suggestion_with_style(
-                                DUMMY_SP,
-                                "raw extern location",
-                                raw.clone(),
-                                Applicability::Unspecified,
-                                SuggestionStyle::CompletelyHidden,
-                            );
-                            Json::String(raw)
-                        }
-                    };
-                    db.tool_only_suggestion_with_metadata(
-                        "json extern location",
-                        Applicability::Unspecified,
-                        json
-                    );
-                }
                 BuiltinLintDiagnostics::ProcMacroBackCompat(note) => {
                     db.note(&note);
                 }

compiler/rustc_lint_defs/src/lib.rs

@@ -9,7 +9,6 @@ use rustc_ast::{AttrId, Attribute};
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
 use rustc_error_messages::MultiSpan;
 use rustc_hir::HirId;
-use rustc_serialize::json::Json;
 use rustc_span::edition::Edition;
 use rustc_span::{sym, symbol::Ident, Span, Symbol};
 use rustc_target::spec::abi::Abi;
@@ -403,13 +402,6 @@ impl<HCX> ToStableHashKey<HCX> for LintId {
     }
 }
 
-// Duplicated from rustc_session::config::ExternDepSpec to avoid cyclic dependency
-#[derive(PartialEq, Debug)]
-pub enum ExternDepSpec {
-    Json(Json),
-    Raw(String),
-}
-
 // This could be a closure, but then implementing derive trait
 // becomes hacky (and it gets allocated).
 #[derive(Debug)]
@@ -427,7 +419,6 @@ pub enum BuiltinLintDiagnostics {
     UnusedBuiltinAttribute { attr_name: Symbol, macro_name: String, invoc_span: Span },
     PatternsInFnsWithoutBody(Span, Ident),
     LegacyDeriveHelpers(Span),
-    ExternDepSpec(String, ExternDepSpec),
     ProcMacroBackCompat(String),
     OrPatternsBackCompat(Span, String),
     ReservedPrefix(Span),

compiler/rustc_metadata/src/creader.rs

@@ -13,11 +13,10 @@ use rustc_hir::def_id::{CrateNum, LocalDefId, StableCrateId, LOCAL_CRATE};
 use rustc_hir::definitions::Definitions;
 use rustc_index::vec::IndexVec;
 use rustc_middle::ty::TyCtxt;
-use rustc_serialize::json::ToJson;
 use rustc_session::config::{self, CrateType, ExternLocation};
 use rustc_session::cstore::{CrateDepKind, CrateSource, ExternCrate};
 use rustc_session::cstore::{ExternCrateSource, MetadataLoaderDyn};
-use rustc_session::lint::{self, BuiltinLintDiagnostics, ExternDepSpec};
+use rustc_session::lint;
 use rustc_session::output::validate_crate_name;
 use rustc_session::search_paths::PathKind;
 use rustc_session::Session;
@@ -27,7 +26,6 @@ use rustc_span::{Span, DUMMY_SP};
 use rustc_target::spec::{PanicStrategy, TargetTriple};
 
 use proc_macro::bridge::client::ProcMacro;
-use std::collections::BTreeMap;
 use std::ops::Fn;
 use std::path::Path;
 use std::{cmp, env};
@@ -919,20 +917,7 @@ impl<'a> CrateLoader<'a> {
                 continue;
             }
 
-            let diag = match self.sess.opts.extern_dep_specs.get(name) {
-                Some(loc) => BuiltinLintDiagnostics::ExternDepSpec(name.clone(), loc.into()),
-                None => {
-                    // If we don't have a specific location, provide a json encoding of the `--extern`
-                    // option.
-                    let meta: BTreeMap<String, String> =
-                        std::iter::once(("name".to_string(), name.to_string())).collect();
-                    BuiltinLintDiagnostics::ExternDepSpec(
-                        name.clone(),
-                        ExternDepSpec::Json(meta.to_json()),
-                    )
-                }
-            };
-            self.sess.parse_sess.buffer_lint_with_diagnostic(
+            self.sess.parse_sess.buffer_lint(
                     lint::builtin::UNUSED_CRATE_DEPENDENCIES,
                     span,
                     ast::CRATE_NODE_ID,
@@ -941,7 +926,6 @@ impl<'a> CrateLoader<'a> {
                         name,
                         self.local_crate_name,
                         name),
-                    diag,
                 );
         }
     }