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

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,

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],