Ship rust-analyzer-proc-macro-srv binary with dist::Rustc

This builds `src/tools/rust-analyzer/crates/proc-macro-srv-cli` and
ships it as part of Rustc's dist component. This allows rust-analyzer's
proc macro support to work on all rustc versions (stable, beta and
nightly) starting now.

src/bootstrap/builder.rs

@@ -601,6 +601,7 @@ impl<'a> Builder<'a> {
                 tool::Cargo,
                 tool::Rls,
                 tool::RustAnalyzer,
+                tool::RustAnalyzerProcMacroSrv,
                 tool::RustDemangler,
                 tool::Rustdoc,
                 tool::Clippy,

src/bootstrap/dist.rs

@@ -362,6 +362,18 @@ impl Step for Rustc {
 
             builder.install(&builder.rustdoc(compiler), &image.join("bin"), 0o755);
 
+            let ra_proc_macro_srv = builder
+                .ensure(tool::RustAnalyzerProcMacroSrv {
+                    compiler: builder.compiler_for(
+                        compiler.stage,
+                        builder.config.build,
+                        compiler.host,
+                    ),
+                    target: compiler.host,
+                })
+                .expect("rust-analyzer-proc-macro-server always builds");
+            builder.install(&ra_proc_macro_srv, &image.join("libexec"), 0o755);
+
             let libdir_relative = builder.libdir_relative(compiler);
 
             // Copy runtime DLLs needed by the compiler

src/bootstrap/tool.rs

@@ -727,6 +727,50 @@ impl Step for RustAnalyzer {
     }
 }
 
+#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
+pub struct RustAnalyzerProcMacroSrv {
+    pub compiler: Compiler,
+    pub target: TargetSelection,
+}
+
+impl Step for RustAnalyzerProcMacroSrv {
+    type Output = Option<PathBuf>;
+    const DEFAULT: bool = true;
+    const ONLY_HOSTS: bool = false;
+
+    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
+        let builder = run.builder;
+        run.path("src/tools/rust-analyzer").default_condition(
+            builder.config.extended
+                && builder
+                    .config
+                    .tools
+                    .as_ref()
+                    .map_or(true, |tools| tools.iter().any(|tool| tool == "rust-analyzer")),
+        )
+    }
+
+    fn make_run(run: RunConfig<'_>) {
+        run.builder.ensure(RustAnalyzerProcMacroSrv {
+            compiler: run.builder.compiler(run.builder.top_stage, run.builder.config.build),
+            target: run.target,
+        });
+    }
+
+    fn run(self, builder: &Builder<'_>) -> Option<PathBuf> {
+        builder.ensure(ToolBuild {
+            compiler: self.compiler,
+            target: self.target,
+            tool: "rust-analyzer-proc-macro-srv",
+            mode: Mode::ToolStd,
+            path: "src/tools/rust-analyzer/crates/proc-macro-srv-cli",
+            extra_features: vec!["proc-macro-srv/sysroot-abi".to_owned()],
+            is_optional_tool: false,
+            source_type: SourceType::InTree,
+        })
+    }
+}
+
 macro_rules! tool_extended {
     (($sel:ident, $builder:ident),
        $($name:ident,