Support env_flags attribute for cargo.rust_library/cargo.rust_binary

* When `buildscript.run = true`, set `env_flags` attribute like
  `env_flags = ["@$(location :my_crate-0.0.0-build-script-run[env_flags])"],`

Signed-off-by: Yuxuan Dai <yxdai@smail.nju.edu.cn>

Author: yxdai-nju

src/buck.rs

@@ -557,6 +557,7 @@ pub struct PlatformRustCommon {
     pub deps: Selectable<UniverseName, BTreeSet<RuleRef>>,
     pub named_deps: Selectable<UniverseName, BTreeMap<String, RuleRef>>,
     pub env: Selectable<UniverseName, BTreeMap<String, StringOrPath>>,
+    pub env_flags: BTreeSet<String>,
 
     // This isn't really "common" (Binaries only), but does need to be platform
     pub link_style: Option<String>,
@@ -575,6 +576,7 @@ impl Serialize for PlatformRustCommon {
             deps,
             named_deps,
             env,
+            env_flags,
             link_style,
             linker_flags,
             preferred_linkage,
@@ -586,6 +588,9 @@ impl Serialize for PlatformRustCommon {
         if !env.is_empty() {
             map.serialize_entry("env", env)?;
         }
+        if !env_flags.is_empty() {
+            map.serialize_entry("env_flags", env_flags)?;
+        }
         if !features.is_empty() {
             map.serialize_entry("features", features)?;
         }
@@ -711,6 +716,7 @@ impl Serialize for RustLibrary {
                             deps,
                             named_deps,
                             env,
+                            env_flags,
                             link_style,
                             linker_flags,
                             preferred_linkage,
@@ -739,6 +745,9 @@ impl Serialize for RustLibrary {
         if !env.is_empty() {
             map.serialize_entry("env", env)?;
         }
+        if !env_flags.is_empty() {
+            map.serialize_entry("env_flags", env_flags)?;
+        }
         if !features.is_empty() {
             map.serialize_entry("features", features)?;
         }
@@ -812,6 +821,7 @@ impl Serialize for RustBinary {
                             deps,
                             named_deps,
                             env,
+                            env_flags,
                             link_style,
                             linker_flags,
                             preferred_linkage,
@@ -833,6 +843,9 @@ impl Serialize for RustBinary {
         if !env.is_empty() {
             map.serialize_entry("env", env)?;
         }
+        if !env_flags.is_empty() {
+            map.serialize_entry("env_flags", env_flags)?;
+        }
         if !features.is_empty() {
             map.serialize_entry("features", features)?;
         }

src/buckify.rs

@@ -657,6 +657,23 @@ fn generate_target_rules<'scope>(
     )
     .context("env")?;
 
+    unzip_platform(
+        config,
+        &mut base,
+        &mut perplat,
+        |rule, flags| {
+            log::debug!(
+                "pkg {} target {}: adding env_flags: {:?}",
+                pkg,
+                tgt.name,
+                flags,
+            );
+            rule.env_flags.extend(flags);
+        },
+        fixups.buildscript_env_flags(),
+    )
+    .context("env_flags")?;
+
     // Compute set of dependencies any rule we generate here will need. They will only
     // be emitted if we actually emit some rules below.
     let mut dep_pkgs = Vec::new();

src/fixups.rs

@@ -954,6 +954,26 @@ impl<'meta> Fixups<'meta> {
         Ok(Some(value))
     }
 
+    /// Additional environment variable settings that are passed through flags
+    pub fn buildscript_env_flags(&self) -> Vec<(Option<PlatformExpr>, BTreeSet<String>)> {
+        let mut ret = vec![];
+        if self.buildscript_target().is_none() {
+            return ret; // no buildscript
+        }
+
+        for (platform, config) in self.fixup_config.configs(&self.package.version) {
+            if !self.target.kind_custom_build() && config.buildscript.run.is_some() {
+                let flags = BTreeSet::from_iter([format!(
+                    "@$(location :{}[env_flags])",
+                    self.buildscript_genrule_name()
+                )]);
+                ret.push((platform.cloned(), flags));
+            }
+        }
+
+        ret
+    }
+
     /// Given a glob for the srcs, walk the filesystem to get the full set.
     /// `srcs` is the normal source glob rooted at the package's manifest dir.
     pub fn compute_srcs(