Pass --extern=proc_macro to Rust procedural macros

Summary:
Rebase of D21840371 with `throws InterruptedException` added to unbreak RustBinaryIntegrationTest.java.

 ---

This diff updates Buck's behavior to match the behavior of Cargo 1.42+ ([rust-lang/cargo#7700](rust-lang/cargo#7700)) to no longer require procedural macro crates to specify "extern crate proc_macro". See the release announcement of this change in https://blog.rust-lang.org/2020/03/12/Rust-1.42.html#use-proc_macrotokenstream-now-works.

Buck technically has no lower compiler version bound on its rustc support, so if someone requires support for rustc <1.42 in Buck then we can consider introducing a buckconfig to opt out of --extern=proc_macro.

Reviewed By: jsgf

fbshipit-source-id: 74fac22e9a67e6967151ab7e38f7e97be7300a4d

Author: David Tolnay

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

@@ -294,6 +294,13 @@ private static RustCompileRule createBuild(
       args.add(StringArg.of("-Zsave-analysis"));
     }
 
+    // Don't require "extern crate proc_macro"
+    if (crateType == CrateType.PROC_MACRO) {
+      // pathless extern was stabilized in 1.42
+      // https://blog.rust-lang.org/2020/03/12/Rust-1.42.html#use-proc_macrotokenstream-now-works
+      args.add(StringArg.of("--extern=proc_macro"));
+    }
+
     if (incremental.isPresent()) {
       Path path =
           projectFilesystem

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

@@ -998,11 +998,13 @@ public void includeFileMissing() throws IOException {
   }
 
   @Test
-  public void procmacroCompile() throws IOException {
+  public void procmacroCompile() throws IOException, InterruptedException {
     ProjectWorkspace workspace =
         TestDataHelper.createProjectWorkspaceForScenario(this, "procmacro", tmp);
     workspace.setUp();
 
+    RustAssumptions.assumeVersion(workspace, "1.42");
+
     assertThat(
         // Check that we can build a procmacro crate
         workspace.runBuckCommand("run", "//:test").assertSuccess("link with procmacro").getStdout(),
@@ -1011,22 +1013,26 @@ public void procmacroCompile() throws IOException {
   }
 
   @Test
-  public void procmacroCompileCheck() throws IOException {
+  public void procmacroCompileCheck() throws IOException, InterruptedException {
     ProjectWorkspace workspace =
         TestDataHelper.createProjectWorkspaceForScenario(this, "procmacro", tmp);
     workspace.setUp();
 
+    RustAssumptions.assumeVersion(workspace, "1.42");
+
     workspace.runBuckBuild("//:test#check").assertSuccess();
     BuckBuildLog buildLog = workspace.getBuildLog();
     buildLog.assertTargetBuiltLocally("//:test#check");
   }
 
   @Test
-  public void procmacroCompileShared() throws IOException {
+  public void procmacroCompileShared() throws IOException, InterruptedException {
     ProjectWorkspace workspace =
         TestDataHelper.createProjectWorkspaceForScenario(this, "procmacro", tmp);
     workspace.setUp();
 
+    RustAssumptions.assumeVersion(workspace, "1.42");
+
     assertThat(
         // Check that we can build a procmacro crate
         workspace
@@ -1038,11 +1044,13 @@ public void procmacroCompileShared() throws IOException {
   }
 
   @Test
-  public void procmacroCompileSharedForceRlib() throws IOException {
+  public void procmacroCompileSharedForceRlib() throws IOException, InterruptedException {
     ProjectWorkspace workspace =
         TestDataHelper.createProjectWorkspaceForScenario(this, "procmacro", tmp);
     workspace.setUp();
 
+    RustAssumptions.assumeVersion(workspace, "1.42");
+
     assertThat(
         // Check that we can build a procmacro crate
         workspace

test/com/facebook/buck/features/rust/testdata/procmacro/BUCK.fixture

@@ -5,6 +5,13 @@ rust_library(
     proc_macro = True,
 )
 
+rust_library(
+    name = "helloworld_derive_no_extern",
+    srcs = ["helloworld_derive_no_extern.rs"],
+    deps = [":hellodep"],
+    proc_macro = True,
+)
+
 rust_library(
     name = "hellodep",
     srcs = ["hellodep.rs"],
@@ -15,6 +22,7 @@ rust_binary(
     srcs = ["main.rs"],
     deps = [
         ":helloworld_derive",
+        ":helloworld_derive_no_extern",
     ],
 )
 
@@ -24,5 +32,6 @@ rust_binary(
     link_style = "shared",
     deps = [
         ":helloworld_derive",
+        ":helloworld_derive_no_extern",
     ],
 )

test/com/facebook/buck/features/rust/testdata/procmacro/helloworld_derive_no_extern.rs

@@ -0,0 +1,10 @@
+extern crate hellodep;
+
+use proc_macro::TokenStream;
+use std::str::FromStr;
+
+#[proc_macro_derive(HelloWorldNoExtern)]
+pub fn hello_world_no_extern(_input: TokenStream) -> TokenStream {
+    println!("hellodep returned: {}", hellodep::hellodep());
+    TokenStream::new(); // no-op
+}

test/com/facebook/buck/features/rust/testdata/procmacro/main.rs

@@ -2,6 +2,7 @@
 
 #[macro_use]
 extern crate helloworld_derive;
+extern crate helloworld_derive_no_extern;
 
 trait HelloWorld {
     fn hello_world();
@@ -13,6 +14,9 @@ struct FrenchToast;
 #[derive(HelloWorld)]
 struct Waffles;
 
+#[derive(HelloWorldNoExtern)]
+struct WafflesNoExtern;
+
 fn main() {
     println!("Hello");
 }