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 https://github.com/rust-lang/rust/pull/72603

3 files changed, 3 insertions, 128 deletions

diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index ecb3cdd627c..2ae599a134b 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/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() {
diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index 0139007da42..d680e7fab70 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/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(),
         }
     }
 }
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index cfad1fc01ab..9168705bcff 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/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)]