buck/rust: remove support for --extern-location

Summary:
`--extern-location` was an experimental option in rustc to pass tool
diagnostic information through rustc. It was used to pass location information
for unused dependencies from Buck via rustc for consumption by rustfixdeps.

This was removed in upstream rust in
rust-lang/rust#96086 so remove support for it here.

Reviewed By: cjhopman

fbshipit-source-id: 3509c3b2680a3a86fc782839f2a12312674f9d52

Author: jsgf

src/com/facebook/buck/features/rust/PrebuiltRustLibraryDescription.java

@@ -42,11 +42,6 @@
 public class PrebuiltRustLibraryDescription
     implements DescriptionWithTargetGraph<PrebuiltRustLibraryDescriptionArg>,
         VersionPropagator<PrebuiltRustLibraryDescriptionArg> {
-  private final RustBuckConfig rustBuckConfig;
-
-  public PrebuiltRustLibraryDescription(RustBuckConfig rustBuckConfig) {
-    this.rustBuckConfig = rustBuckConfig;
-  }
 
   @Override
   public Class<PrebuiltRustLibraryDescriptionArg> getConstructorArgType() {
@@ -88,8 +83,7 @@ public com.facebook.buck.rules.args.Arg getLinkerArg(
             ruleFlags,
             args.getRlib(),
             directDependent,
-            dependentFilesystem.relativize(rlibAbsolutePath).toString(),
-            rustBuckConfig.getExternLocations());
+            dependentFilesystem.relativize(rlibAbsolutePath).toString());
       }
 
       @Override

src/com/facebook/buck/features/rust/RustBuckConfig.java

@@ -50,7 +50,6 @@ public class RustBuckConfig {
   private static final String PREFER_STATIC_LIBS = "prefer_static_libs";
   private static final String RUSTC_INCREMENTAL = "incremental";
   private static final String DEFAULT_EDITION = "default_edition";
-  private static final String EXTERN_LOCATIONS = "extern_locations";
   private static final String RUSTC_PLUGIN_PLATFORM = "rustc_plugin_platform";
   private static final String NATIVE_UNBUNDLE_DEPS = "native_unbundle_deps";
 
@@ -230,18 +229,6 @@ boolean getUnflavoredBinaries() {
     return delegate.getBooleanValue(SECTION, UNFLAVORED_BINARIES, false);
   }
 
-  /**
-   * Get extern_locations option. This controls whether to pass `--extern-location` to rustc for
-   * each `--extern` so that when it reports an unused dependency it can refer to the actual Buck
-   * target and dependency in question. The location is a json object with `target` (unflavored
-   * build target) and `dep` (unflavored dependency for target) keys.
-   *
-   * @return Boolean of whether to pass --extern-location to rustc.
-   */
-  boolean getExternLocations() {
-    return delegate.getBooleanValue(SECTION, EXTERN_LOCATIONS, false);
-  }
-
   /**
    * Get source path remapping option. This controls whether we ask rustc to remap source paths in
    * all output (ie, compiler messages, file!() macros, debug info, etc).

src/com/facebook/buck/features/rust/RustDescriptionsProvider.java

@@ -40,6 +40,6 @@ public Collection<Description<?>> getDescriptions(DescriptionCreationContext con
         new RustBinaryDescription(toolchainProvider, rustBuckConfig, downwardApiConfig),
         new RustLibraryDescription(toolchainProvider, rustBuckConfig, downwardApiConfig),
         new RustTestDescription(toolchainProvider, rustBuckConfig, downwardApiConfig),
-        new PrebuiltRustLibraryDescription(rustBuckConfig));
+        new PrebuiltRustLibraryDescription());
   }
 }

src/com/facebook/buck/features/rust/RustLibraryArg.java

@@ -36,11 +36,6 @@
  * referenced by. Indirect dependencies are not explicitly enumerated; instead the `-Ldependency`
  * option adds a search directory in which dependencies can be found (in practice with Buck builds,
  * there's one directory per dependency).
- *
- * <p>We also keep the target name we're adding the dependency for, and the target a dependent crate
- * comes from. This is so we can pass an `--extern-location` option to rustc which allows compiler
- * diagnostics for unused dependencies to directly reference the dependency which needs to be
- * removed.
  */
 @BuckStyleValue
 public abstract class RustLibraryArg implements Arg, HasSourcePath {
@@ -70,20 +65,15 @@ public abstract class RustLibraryArg implements Arg, HasSourcePath {
   @AddToRuleKey
   public abstract String getRlibRelativePath();
 
-  /// True if the `extern_locations` option is set.
-  @AddToRuleKey
-  public abstract boolean getExternLoc();
-
   public static RustLibraryArg of(
       BuildTarget target,
       String crate,
       ImmutableList<String> flags,
       SourcePath rlib,
       Optional<BuildTarget> directDependent,
-      String rlibRelativePath,
-      boolean extern_loc) {
+      String rlibRelativePath) {
     return ImmutableRustLibraryArg.ofImpl(
-        target, crate, flags, rlib, directDependent, rlibRelativePath, extern_loc);
+        target, crate, flags, rlib, directDependent, rlibRelativePath);
   }
 
   @Override
@@ -108,15 +98,6 @@ public void appendToCommandLine(
 
       consumer.accept(
           String.format("--extern=%s%s=%s", externQualifiers, crate, getRlibRelativePath()));
-      if (getExternLoc()) {
-        // assume targets never need json string quoting
-        consumer.accept(
-            String.format(
-                "--extern-location=%s=json:{\"target\":\"%s\",\"dep\":\"%s\"}",
-                crate,
-                directDep.get().withoutFlavors().getFullyQualifiedName(),
-                getTarget().getFullyQualifiedName()));
-      }
     } else {
       consumer.accept(
           String.format("-Ldependency=%s", Paths.get(getRlibRelativePath()).getParent()));

src/com/facebook/buck/features/rust/RustLibraryDescription.java

@@ -357,8 +357,7 @@ public Arg getLinkerArg(
               ruleFlags,
               rlib,
               directDependent,
-              dependentFilesystem.relativize(rlibAbsolutePath).toString(),
-              rustBuckConfig.getExternLocations());
+              dependentFilesystem.relativize(rlibAbsolutePath).toString());
         }
 
         @Override

test/com/facebook/buck/features/rust/PrebuiltRustLibraryBuilder.java

@@ -16,7 +16,6 @@
 
 package com.facebook.buck.features.rust;
 
-import com.facebook.buck.core.config.FakeBuckConfig;
 import com.facebook.buck.core.model.BuildTarget;
 import com.facebook.buck.core.model.BuildTargetFactory;
 import com.facebook.buck.core.model.targetgraph.AbstractNodeBuilder;
@@ -37,9 +36,8 @@ private PrebuiltRustLibraryBuilder(
   }
 
   public static PrebuiltRustLibraryBuilder from(String target) {
-    RustBuckConfig config = new RustBuckConfig(FakeBuckConfig.builder().build());
     return new PrebuiltRustLibraryBuilder(
-        new PrebuiltRustLibraryDescription(config), BuildTargetFactory.newInstance(target));
+        new PrebuiltRustLibraryDescription(), BuildTargetFactory.newInstance(target));
   }
 
   public PrebuiltRustLibraryBuilder setRlib(SourcePath rlib) {