Rollup merge of #96086 - jsgf:remove-extern-location, r=davidtwco

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

36 files changed, 6 insertions, 517 deletions

diff --git a/Cargo.lock b/Cargo.lock
index e908520ef69..e3a9eb34936 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3934,7 +3934,6 @@ dependencies = [
  "rustc_infer",
  "rustc_middle",
  "rustc_parse_format",
- "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 9cd072c8b4c..cd17726c785 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 d7c5df7d8e2..339bcc24751 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)]
diff --git a/compiler/rustc_lint/Cargo.toml b/compiler/rustc_lint/Cargo.toml
index 8ea47dda928..02f747eeccc 100644
--- a/compiler/rustc_lint/Cargo.toml
+++ b/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" }
diff --git a/compiler/rustc_lint/src/context.rs b/compiler/rustc_lint/src/context.rs
index 152c53dac7f..0ffa65b79b5 100644
--- a/compiler/rustc_lint/src/context.rs
+++ b/compiler/rustc_lint/src/context.rs
@@ -33,8 +33,7 @@ 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;
@@ -728,30 +727,6 @@ 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);
                 }
diff --git a/compiler/rustc_lint_defs/src/lib.rs b/compiler/rustc_lint_defs/src/lib.rs
index 4debbf26be6..bde773a32db 100644
--- a/compiler/rustc_lint_defs/src/lib.rs
+++ b/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)]
@@ -428,7 +420,6 @@ 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),
diff --git a/compiler/rustc_metadata/src/creader.rs b/compiler/rustc_metadata/src/creader.rs
index 566d27212d0..e5d0cd28925 100644
--- a/compiler/rustc_metadata/src/creader.rs
+++ b/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};
@@ -920,20 +918,7 @@ 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,
@@ -942,7 +927,6 @@ impl<'a> CrateLoader<'a> {
                         name,
                         self.local_crate_name,
                         name),
-                    diag,
                 );
         }
     }
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 5a447aa6237..86a078f4a38 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -15,8 +15,6 @@ use rustc_target::abi::{Align, TargetDataLayout};
 use rustc_target::spec::{LinkerFlavor, SplitDebuginfo, Target, TargetTriple, TargetWarnings};
 use rustc_target::spec::{PanicStrategy, SanitizerSet, TARGETS};
 
-use rustc_serialize::json;
-
 use crate::parse::{CrateCheckConfig, CrateConfig};
 use rustc_feature::UnstableFeatures;
 use rustc_span::edition::{Edition, DEFAULT_EDITION, EDITION_NAME_LIST, LATEST_STABLE_EDITION};
@@ -460,9 +458,6 @@ impl OutputTypes {
 #[derive(Clone)]
 pub struct Externs(BTreeMap<String, ExternEntry>);
 
-#[derive(Clone)]
-pub struct ExternDepSpecs(BTreeMap<String, ExternDepSpec>);
-
 #[derive(Clone, Debug)]
 pub struct ExternEntry {
     pub location: ExternLocation,
@@ -494,27 +489,6 @@ pub enum ExternLocation {
     ExactPaths(BTreeSet<CanonicalizedPath>),
 }
 
-/// Supplied source location of a dependency - for example in a build specification
-/// file like Cargo.toml. We support several syntaxes: if it makes sense to reference
-/// a file and line, then the build system can specify that. On the other hand, it may
-/// make more sense to have an arbitrary raw string.
-#[derive(Clone, PartialEq)]
-pub enum ExternDepSpec {
-    /// Raw string
-    Raw(String),
-    /// Raw data in json format
-    Json(json::Json),
-}
-
-impl<'a> From<&'a ExternDepSpec> for rustc_lint_defs::ExternDepSpec {
-    fn from(from: &'a ExternDepSpec) -> Self {
-        match from {
-            ExternDepSpec::Raw(s) => rustc_lint_defs::ExternDepSpec::Raw(s.clone()),
-            ExternDepSpec::Json(json) => rustc_lint_defs::ExternDepSpec::Json(json.clone()),
-        }
-    }
-}
-
 impl Externs {
     /// Used for testing.
     pub fn new(data: BTreeMap<String, ExternEntry>) -> Externs {
@@ -547,25 +521,6 @@ impl ExternEntry {
     }
 }
 
-impl ExternDepSpecs {
-    pub fn new(data: BTreeMap<String, ExternDepSpec>) -> ExternDepSpecs {
-        ExternDepSpecs(data)
-    }
-
-    pub fn get(&self, key: &str) -> Option<&ExternDepSpec> {
-        self.0.get(key)
-    }
-}
-
-impl fmt::Display for ExternDepSpec {
-    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            ExternDepSpec::Raw(raw) => fmt.write_str(raw),
-            ExternDepSpec::Json(json) => json::as_json(json).fmt(fmt),
-        }
-    }
-}
-
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub enum PrintRequest {
     FileNames,
@@ -785,7 +740,6 @@ impl Default for Options {
             cg: Default::default(),
             error_format: ErrorOutputType::default(),
             externs: Externs(BTreeMap::new()),
-            extern_dep_specs: ExternDepSpecs(BTreeMap::new()),
             crate_name: None,
             libs: Vec::new(),
             unstable_features: UnstableFeatures::Disallow,
@@ -1454,12 +1408,6 @@ pub fn rustc_optgroups() -> Vec<RustcOptGroup> {
             "Specify where an external rust library is located",
             "NAME[=PATH]",
         ),
-        opt::multi_s(
-            "",
-            "extern-location",
-            "Location where an external crate dependency is specified",
-            "NAME=LOCATION",
-        ),
         opt::opt_s("", "sysroot", "Override the system root", "PATH"),
         opt::multi("Z", "", "Set internal debugging options", "FLAG"),
         opt::opt_s(
@@ -2221,68 +2169,6 @@ pub fn parse_externs(
     Externs(externs)
 }
 
-fn parse_extern_dep_specs(
-    matches: &getopts::Matches,
-    debugging_opts: &DebuggingOptions,
-    error_format: ErrorOutputType,
-) -> ExternDepSpecs {
-    let is_unstable_enabled = debugging_opts.unstable_options;
-    let mut map = BTreeMap::new();
-
-    for arg in matches.opt_strs("extern-location") {
-        if !is_unstable_enabled {
-            early_error(
-                error_format,
-                "`--extern-location` option is unstable: set `-Z unstable-options`",
-            );
-        }
-
-        let mut parts = arg.splitn(2, '=');
-        let name = parts.next().unwrap_or_else(|| {
-            early_error(error_format, "`--extern-location` value must not be empty")
-        });
-        let loc = parts.next().unwrap_or_else(|| {
-            early_error(
-                error_format,
-                &format!("`--extern-location`: specify location for extern crate `{name}`"),
-            )
-        });
-
-        let locparts: Vec<_> = loc.split(':').collect();
-        let spec = match &locparts[..] {
-            ["raw", ..] => {
-                // Don't want `:` split string
-                let raw = loc.splitn(2, ':').nth(1).unwrap_or_else(|| {
-                    early_error(error_format, "`--extern-location`: missing `raw` location")
-                });
-                ExternDepSpec::Raw(raw.to_string())
-            }
-            ["json", ..] => {
-                // Don't want `:` split string
-                let raw = loc.splitn(2, ':').nth(1).unwrap_or_else(|| {
-                    early_error(error_format, "`--extern-location`: missing `json` location")
-                });
-                let json = json::from_str(raw).unwrap_or_else(|_| {
-                    early_error(
-                        error_format,
-                        &format!("`--extern-location`: malformed json location `{raw}`"),
-                    )
-                });
-                ExternDepSpec::Json(json)
-            }
-            [bad, ..] => early_error(
-                error_format,
-                &format!("unknown location type `{bad}`: use `raw` or `json`"),
-            ),
-            [] => early_error(error_format, "missing location specification"),
-        };
-
-        map.insert(name.to_string(), spec);
-    }
-
-    ExternDepSpecs::new(map)
-}
-
 fn parse_remap_path_prefix(
     matches: &getopts::Matches,
     debugging_opts: &DebuggingOptions,
@@ -2525,7 +2411,6 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
     }
 
     let externs = parse_externs(matches, &debugging_opts, error_format);
-    let extern_dep_specs = parse_extern_dep_specs(matches, &debugging_opts, error_format);
 
     let crate_name = matches.opt_str("crate-name");
 
@@ -2601,7 +2486,6 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
         error_format,
         externs,
         unstable_features: UnstableFeatures::from_environment(crate_name.as_deref()),
-        extern_dep_specs,
         crate_name,
         libs,
         debug_assertions,
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 4994f8eaeb2..df65409a8a0 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -183,7 +183,6 @@ top_level_options!(
         borrowck_mode: BorrowckMode [UNTRACKED],
         cg: CodegenOptions [SUBSTRUCT],
         externs: Externs [UNTRACKED],
-        extern_dep_specs: ExternDepSpecs [UNTRACKED],
         crate_name: Option<String> [TRACKED],
         /// Indicates how the compiler should treat unstable features.
         unstable_features: UnstableFeatures [TRACKED],
diff --git a/src/doc/unstable-book/src/compiler-flags/extern-location.md b/src/doc/unstable-book/src/compiler-flags/extern-location.md
deleted file mode 100644
index 1c80d5426bf..00000000000
--- a/src/doc/unstable-book/src/compiler-flags/extern-location.md
+++ /dev/null
@@ -1,31 +0,0 @@
-# `extern-location`
-
-MCP for this feature: [#303]
-
-[#303]: https://github.com/rust-lang/compiler-team/issues/303
-
-------------------------
-
-The `unused-extern-crates` lint reports when a crate was specified on the rustc
-command-line with `--extern name=path` but no symbols were referenced in it.
-This is useful to know, but it's hard to map that back to a specific place a user
-or tool could fix (ie, to remove the unused dependency).
-
-The `--extern-location` flag allows the build system to associate a location with
-the `--extern` option, which is then emitted as part of the diagnostics. This location
-is abstract and just round-tripped through rustc; the compiler never attempts to
-interpret it in any way.
-
-There are two supported forms of location: a bare string, or a blob of json:
-- `--extern-location foo=raw:Makefile:123` would associate the raw string `Makefile:123`
-- `--extern-location 'bar=json:{"target":"//my_project:library","dep":"//common:serde"}` would
-  associate the json structure with `--extern bar=<path>`, indicating which dependency of
-  which rule introduced the unused extern crate.
-
-This primarily intended to be used with tooling - for example a linter which can automatically
-remove unused dependencies - rather than being directly presented to users.
-
-`raw` locations are presented as part of the normal rendered diagnostics and included in
-the json form. `json` locations are only included in the json form of diagnostics,
-as a `tool_metadata` field. For `raw` locations `tool_metadata` is simply a json string,
-whereas `json` allows the rustc invoker to fully control its form and content.
diff --git a/src/test/ui/unused-crate-deps/extern-loc-bad-loctype.rs b/src/test/ui/unused-crate-deps/extern-loc-bad-loctype.rs
deleted file mode 100644
index e69df0359fd..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-bad-loctype.rs
+++ /dev/null
@@ -1,8 +0,0 @@
-// --extern-location with bad location type
-
-// aux-crate:bar=bar.rs
-// compile-flags:--extern-location bar=badloc:in-the-test-file -Z unstable-options
-
-#![warn(unused_crate_dependencies)]
-
-fn main() {}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-bad-loctype.stderr b/src/test/ui/unused-crate-deps/extern-loc-bad-loctype.stderr
deleted file mode 100644
index 12378f12557..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-bad-loctype.stderr
+++ /dev/null
@@ -1,2 +0,0 @@
-error: unknown location type `badloc`: use `raw` or `json`
-
diff --git a/src/test/ui/unused-crate-deps/extern-loc-defl-json.rs b/src/test/ui/unused-crate-deps/extern-loc-defl-json.rs
deleted file mode 100644
index a023f535b81..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-defl-json.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-// Default extern location from name and path if one isn't specified
-
-// check-pass
-// aux-crate:bar=bar.rs
-// compile-flags:--error-format json
-
-#![warn(unused_crate_dependencies)]
-//~^ WARNING external crate `bar` unused in
-
-fn main() {}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-defl-json.stderr b/src/test/ui/unused-crate-deps/extern-loc-defl-json.stderr
deleted file mode 100644
index cee3f6c1495..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-defl-json.stderr
+++ /dev/null
@@ -1,17 +0,0 @@
-{"message":"external crate `bar` unused in `extern_loc_defl_json`: remove the dependency or add `use bar as _;`","code":{"code":"unused_crate_dependencies","explanation":null},"level":"warning","spans":[{"file_name":"$DIR/extern-loc-defl-json.rs","byte_start":146,"byte_end":146,"line_start":7,"line_end":7,"column_start":1,"column_end":1,"is_primary":true,"text":[{"text":"#![warn(unused_crate_dependencies)]","highlight_start":1,"highlight_end":1}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"the lint level is defined here","code":null,"level":"note","spans":[{"file_name":"$DIR/extern-loc-defl-json.rs","byte_start":154,"byte_end":179,"line_start":7,"line_end":7,"column_start":9,"column_end":34,"is_primary":true,"text":[{"text":"#![warn(unused_crate_dependencies)]","highlight_start":9,"highlight_end":34}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":null},{"message":"remove unnecessary dependency `bar`","code":null,"level":"help","spans":[],"children":[],"rendered":null},{"message":"json extern location","code":null,"level":"help","spans":[],"children":[],"rendered":null,"tool_metadata":{"name":"bar"}}],"rendered":"warning: external crate `bar` unused in `extern_loc_defl_json`: remove the dependency or add `use bar as _;`
-  --> $DIR/extern-loc-defl-json.rs:7:1
-   |
-LL | #![warn(unused_crate_dependencies)]
-   | ^
-   |
-note: the lint level is defined here
-  --> $DIR/extern-loc-defl-json.rs:7:9
-   |
-LL | #![warn(unused_crate_dependencies)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
-   = help: remove unnecessary dependency `bar`
-
-"}
-{"message":"1 warning emitted","code":null,"level":"warning","spans":[],"children":[],"rendered":"warning: 1 warning emitted
-
-"}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-json-bad-json.rs b/src/test/ui/unused-crate-deps/extern-loc-json-bad-json.rs
deleted file mode 100644
index aee6233e428..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-json-bad-json.rs
+++ /dev/null
@@ -1,8 +0,0 @@
-// --extern-location with a raw reference
-
-// aux-crate:bar=bar.rs
-// compile-flags:--extern-location bar=json:[{"malformed -Z unstable-options
-
-#![warn(unused_crate_dependencies)]
-
-fn main() {}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-json-bad-json.stderr b/src/test/ui/unused-crate-deps/extern-loc-json-bad-json.stderr
deleted file mode 100644
index 20d606372e0..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-json-bad-json.stderr
+++ /dev/null
@@ -1,2 +0,0 @@
-error: `--extern-location`: malformed json location `[{"malformed`
-
diff --git a/src/test/ui/unused-crate-deps/extern-loc-json-json.rs b/src/test/ui/unused-crate-deps/extern-loc-json-json.rs
deleted file mode 100644
index c7988cd469e..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-json-json.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-// --extern-location with a raw reference
-
-// check-pass
-// aux-crate:bar=bar.rs
-// compile-flags:--extern-location bar=json:{"key":123,"value":{}} --error-format json -Z unstable-options
-
-#![warn(unused_crate_dependencies)]
-//~^ WARNING external crate `bar` unused in
-
-fn main() {}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-json-json.stderr b/src/test/ui/unused-crate-deps/extern-loc-json-json.stderr
deleted file mode 100644
index 001ec6a2554..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-json-json.stderr
+++ /dev/null
@@ -1,17 +0,0 @@
-{"message":"external crate `bar` unused in `extern_loc_json_json`: remove the dependency or add `use bar as _;`","code":{"code":"unused_crate_dependencies","explanation":null},"level":"warning","spans":[{"file_name":"$DIR/extern-loc-json-json.rs","byte_start":189,"byte_end":189,"line_start":7,"line_end":7,"column_start":1,"column_end":1,"is_primary":true,"text":[{"text":"#![warn(unused_crate_dependencies)]","highlight_start":1,"highlight_end":1}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"the lint level is defined here","code":null,"level":"note","spans":[{"file_name":"$DIR/extern-loc-json-json.rs","byte_start":197,"byte_end":222,"line_start":7,"line_end":7,"column_start":9,"column_end":34,"is_primary":true,"text":[{"text":"#![warn(unused_crate_dependencies)]","highlight_start":9,"highlight_end":34}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":null},{"message":"remove unnecessary dependency `bar`","code":null,"level":"help","spans":[],"children":[],"rendered":null},{"message":"json extern location","code":null,"level":"help","spans":[],"children":[],"rendered":null,"tool_metadata":{"key":123,"value":{}}}],"rendered":"warning: external crate `bar` unused in `extern_loc_json_json`: remove the dependency or add `use bar as _;`
-  --> $DIR/extern-loc-json-json.rs:7:1
-   |
-LL | #![warn(unused_crate_dependencies)]
-   | ^
-   |
-note: the lint level is defined here
-  --> $DIR/extern-loc-json-json.rs:7:9
-   |
-LL | #![warn(unused_crate_dependencies)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
-   = help: remove unnecessary dependency `bar`
-
-"}
-{"message":"1 warning emitted","code":null,"level":"warning","spans":[],"children":[],"rendered":"warning: 1 warning emitted
-
-"}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-json.rs b/src/test/ui/unused-crate-deps/extern-loc-json.rs
deleted file mode 100644
index c0d76c86b89..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-json.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-// --extern-location with a raw reference
-
-// check-pass
-// aux-crate:bar=bar.rs
-// compile-flags:--extern-location bar=json:{"key":123,"value":{}} -Z unstable-options
-
-#![warn(unused_crate_dependencies)]
-//~^ WARNING external crate `bar` unused in
-
-fn main() {}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-json.stderr b/src/test/ui/unused-crate-deps/extern-loc-json.stderr
deleted file mode 100644
index a6bbc0da1c6..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-json.stderr
+++ /dev/null
@@ -1,15 +0,0 @@
-warning: external crate `bar` unused in `extern_loc_json`: remove the dependency or add `use bar as _;`
-  --> $DIR/extern-loc-json.rs:7:1
-   |
-LL | #![warn(unused_crate_dependencies)]
-   | ^
-   |
-note: the lint level is defined here
-  --> $DIR/extern-loc-json.rs:7:9
-   |
-LL | #![warn(unused_crate_dependencies)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
-   = help: remove unnecessary dependency `bar`
-
-warning: 1 warning emitted
-
diff --git a/src/test/ui/unused-crate-deps/extern-loc-missing-loc.rs b/src/test/ui/unused-crate-deps/extern-loc-missing-loc.rs
deleted file mode 100644
index 6ac558974d0..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-missing-loc.rs
+++ /dev/null
@@ -1,8 +0,0 @@
-// --extern-location with a raw reference
-
-// aux-crate:bar=bar.rs
-// compile-flags:--extern-location bar -Zunstable-options
-
-#![warn(unused_crate_dependencies)]
-
-fn main() {}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-missing-loc.stderr b/src/test/ui/unused-crate-deps/extern-loc-missing-loc.stderr
deleted file mode 100644
index 4584fbfb67f..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-missing-loc.stderr
+++ /dev/null
@@ -1,2 +0,0 @@
-error: `--extern-location`: specify location for extern crate `bar`
-
diff --git a/src/test/ui/unused-crate-deps/extern-loc-missing-loctype.rs b/src/test/ui/unused-crate-deps/extern-loc-missing-loctype.rs
deleted file mode 100644
index 3590b9c2812..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-missing-loctype.rs
+++ /dev/null
@@ -1,8 +0,0 @@
-// --extern-location with no type
-
-// aux-crate:bar=bar.rs
-// compile-flags:--extern-location bar=missing-loc-type -Z unstable-options
-
-#![warn(unused_crate_dependencies)]
-
-fn main() {}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-missing-loctype.stderr b/src/test/ui/unused-crate-deps/extern-loc-missing-loctype.stderr
deleted file mode 100644
index d0c36ebeb14..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-missing-loctype.stderr
+++ /dev/null
@@ -1,2 +0,0 @@
-error: unknown location type `missing-loc-type`: use `raw` or `json`
-
diff --git a/src/test/ui/unused-crate-deps/extern-loc-raw-json.rs b/src/test/ui/unused-crate-deps/extern-loc-raw-json.rs
deleted file mode 100644
index 64c3d77ce08..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-raw-json.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-// --extern-location with a raw reference
-
-// check-pass
-// aux-crate:bar=bar.rs
-// compile-flags:--extern-location bar=raw:in-the-test-file --error-format json -Z unstable-options
-
-#![warn(unused_crate_dependencies)]
-//~^ WARNING external crate `bar` unused in
-
-fn main() {}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-raw-json.stderr b/src/test/ui/unused-crate-deps/extern-loc-raw-json.stderr
deleted file mode 100644
index 4083bd51835..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-raw-json.stderr
+++ /dev/null
@@ -1,17 +0,0 @@
-{"message":"external crate `bar` unused in `extern_loc_raw_json`: remove the dependency or add `use bar as _;`","code":{"code":"unused_crate_dependencies","explanation":null},"level":"warning","spans":[{"file_name":"$DIR/extern-loc-raw-json.rs","byte_start":182,"byte_end":182,"line_start":7,"line_end":7,"column_start":1,"column_end":1,"is_primary":true,"text":[{"text":"#![warn(unused_crate_dependencies)]","highlight_start":1,"highlight_end":1}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[{"message":"the lint level is defined here","code":null,"level":"note","spans":[{"file_name":"$DIR/extern-loc-raw-json.rs","byte_start":190,"byte_end":215,"line_start":7,"line_end":7,"column_start":9,"column_end":34,"is_primary":true,"text":[{"text":"#![warn(unused_crate_dependencies)]","highlight_start":9,"highlight_end":34}],"label":null,"suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":null},{"message":"remove unnecessary dependency `bar` at `in-the-test-file`","code":null,"level":"help","spans":[],"children":[],"rendered":null},{"message":"raw extern location","code":null,"level":"help","spans":[{"file_name":"$DIR/extern-loc-raw-json.rs","byte_start":0,"byte_end":0,"line_start":1,"line_end":1,"column_start":1,"column_end":1,"is_primary":true,"text":[],"label":null,"suggested_replacement":"in-the-test-file","suggestion_applicability":"Unspecified","expansion":null}],"children":[],"rendered":null},{"message":"json extern location","code":null,"level":"help","spans":[],"children":[],"rendered":null,"tool_metadata":"in-the-test-file"}],"rendered":"warning: external crate `bar` unused in `extern_loc_raw_json`: remove the dependency or add `use bar as _;`
-  --> $DIR/extern-loc-raw-json.rs:7:1
-   |
-LL | #![warn(unused_crate_dependencies)]
-   | ^
-   |
-note: the lint level is defined here
-  --> $DIR/extern-loc-raw-json.rs:7:9
-   |
-LL | #![warn(unused_crate_dependencies)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
-   = help: remove unnecessary dependency `bar` at `in-the-test-file`
-
-"}
-{"message":"1 warning emitted","code":null,"level":"warning","spans":[],"children":[],"rendered":"warning: 1 warning emitted
-
-"}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-raw-missing-loc.rs b/src/test/ui/unused-crate-deps/extern-loc-raw-missing-loc.rs
deleted file mode 100644
index a9e7afbda31..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-raw-missing-loc.rs
+++ /dev/null
@@ -1,8 +0,0 @@
-// --extern-location with a raw reference
-
-// aux-crate:bar=bar.rs
-// compile-flags:--extern-location bar=raw -Z unstable-options
-
-#![warn(unused_crate_dependencies)]
-
-fn main() {}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-raw-missing-loc.stderr b/src/test/ui/unused-crate-deps/extern-loc-raw-missing-loc.stderr
deleted file mode 100644
index 4b51266e4f6..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-raw-missing-loc.stderr
+++ /dev/null
@@ -1,2 +0,0 @@
-error: `--extern-location`: missing `raw` location
-
diff --git a/src/test/ui/unused-crate-deps/extern-loc-raw.rs b/src/test/ui/unused-crate-deps/extern-loc-raw.rs
deleted file mode 100644
index 27d0975d01a..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-raw.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-// --extern-location with a raw reference
-
-// check-pass
-// aux-crate:bar=bar.rs
-// compile-flags:--extern-location bar=raw:in-the-test-file -Z unstable-options
-
-#![warn(unused_crate_dependencies)]
-//~^ WARNING external crate `bar` unused in
-
-fn main() {}
diff --git a/src/test/ui/unused-crate-deps/extern-loc-raw.stderr b/src/test/ui/unused-crate-deps/extern-loc-raw.stderr
deleted file mode 100644
index 2cdd0055866..00000000000
--- a/src/test/ui/unused-crate-deps/extern-loc-raw.stderr
+++ /dev/null
@@ -1,15 +0,0 @@
-warning: external crate `bar` unused in `extern_loc_raw`: remove the dependency or add `use bar as _;`
-  --> $DIR/extern-loc-raw.rs:7:1
-   |
-LL | #![warn(unused_crate_dependencies)]
-   | ^
-   |
-note: the lint level is defined here
-  --> $DIR/extern-loc-raw.rs:7:9
-   |
-LL | #![warn(unused_crate_dependencies)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
-   = help: remove unnecessary dependency `bar` at `in-the-test-file`
-
-warning: 1 warning emitted
-
diff --git a/src/test/ui/unused-crate-deps/libfib.stderr b/src/test/ui/unused-crate-deps/libfib.stderr
index 479f51bff46..15833126bd6 100644
--- a/src/test/ui/unused-crate-deps/libfib.stderr
+++ b/src/test/ui/unused-crate-deps/libfib.stderr
@@ -5,7 +5,6 @@ LL | pub fn fib(n: u32) -> Vec<u32> {
    | ^
    |
    = note: requested on the command line with `-W unused-crate-dependencies`
-   = help: remove unnecessary dependency `bar`
 
 warning: 1 warning emitted
 
diff --git a/src/test/ui/unused-crate-deps/unused-aliases.stderr b/src/test/ui/unused-crate-deps/unused-aliases.stderr
index 1142d156d0e..c8c6c4507b0 100644
--- a/src/test/ui/unused-crate-deps/unused-aliases.stderr
+++ b/src/test/ui/unused-crate-deps/unused-aliases.stderr
@@ -9,7 +9,6 @@ note: the lint level is defined here
    |
 LL | #![warn(unused_crate_dependencies)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^
-   = help: remove unnecessary dependency `barbar`
 
 warning: 1 warning emitted
 
diff --git a/src/test/ui/unused-crate-deps/warn-attr.stderr b/src/test/ui/unused-crate-deps/warn-attr.stderr
index 29667d9525c..0d38315704b 100644
--- a/src/test/ui/unused-crate-deps/warn-attr.stderr
+++ b/src/test/ui/unused-crate-deps/warn-attr.stderr
@@ -9,7 +9,6 @@ note: the lint level is defined here
    |
 LL | #![warn(unused_crate_dependencies)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^
-   = help: remove unnecessary dependency `bar`
 
 warning: 1 warning emitted
 
diff --git a/src/test/ui/unused-crate-deps/warn-cmdline-static.stderr b/src/test/ui/unused-crate-deps/warn-cmdline-static.stderr
index 2c0c9215129..65956461d64 100644
--- a/src/test/ui/unused-crate-deps/warn-cmdline-static.stderr
+++ b/src/test/ui/unused-crate-deps/warn-cmdline-static.stderr
@@ -5,7 +5,6 @@ LL | fn main() {}
    | ^
    |
    = note: requested on the command line with `-W unused-crate-dependencies`
-   = help: remove unnecessary dependency `bar`
 
 warning: 1 warning emitted
 
diff --git a/src/test/ui/unused-crate-deps/warn-cmdline.stderr b/src/test/ui/unused-crate-deps/warn-cmdline.stderr
index 2cd49218f5a..ea675ba9a1e 100644
--- a/src/test/ui/unused-crate-deps/warn-cmdline.stderr
+++ b/src/test/ui/unused-crate-deps/warn-cmdline.stderr
@@ -5,7 +5,6 @@ LL | fn main() {}
    | ^
    |
    = note: requested on the command line with `-W unused-crate-dependencies`
-   = help: remove unnecessary dependency `bar`
 
 warning: 1 warning emitted