feat(build): emit PIO-compatible build_info.json for downstream tooling (#297)

crates/fbuild-build/src/avr/avr_linker.rs

@@ -134,6 +134,14 @@ impl Linker for AvrLinker {
         &self.size_path
     }
 
+    fn ar_path(&self) -> Option<&Path> {
+        Some(&self.ar_path)
+    }
+
+    fn objcopy_path(&self) -> Option<&Path> {
+        Some(&self.objcopy_path)
+    }
+
     fn report_size(&self, elf_path: &Path) -> Result<SizeInfo> {
         crate::linker::LinkerBase::report_size(
             &self.size_path,

crates/fbuild-build/src/avr/orchestrator.rs

@@ -223,6 +223,22 @@ impl BuildOrchestrator for AvrOrchestrator {
 
         let mcu_config = super::mcu_config::get_avr_config()?;
 
+        // Snapshot for the optional build_info.json emitter — captured
+        // before `defines` is moved into the compiler. See
+        // FastLED/fbuild#297.
+        let info_snapshot = if params.emit_build_info {
+            Some(crate::build_info::BuildInfoSnapshot {
+                board: ctx.board.clone(),
+                defines: defines.clone(),
+                include_dirs: include_dirs.clone(),
+                sketch_sources: sources.sketch_sources.clone(),
+                link_flags: ctx.overlay_link_flags.clone(),
+                link_libs: ctx.overlay_link_libs.clone(),
+            })
+        } else {
+            None
+        };
+
         let compiler = AvrCompiler::new(
             toolchain.get_gcc_path(),
             toolchain.get_gxx_path(),
@@ -286,6 +302,39 @@ impl BuildOrchestrator for AvrOrchestrator {
             start,
         )?;
 
+        // Emit build_info.json (PIO-compatible) for downstream FastLED
+        // tooling when the caller opted in. See FastLED/fbuild#297.
+        if let Some(snap) = info_snapshot {
+            if build_result.success {
+                let example_name = params
+                    .example_name
+                    .clone()
+                    .or_else(|| crate::build_info::default_example_name(&params.project_dir));
+                let inputs = crate::build_info::OrchestratorBuildInfoInputs {
+                    project_dir: &params.project_dir,
+                    env_name: &params.env_name,
+                    board: &snap.board,
+                    compiler: &compiler,
+                    linker: &linker,
+                    include_dirs: &snap.include_dirs,
+                    defines: &snap.defines,
+                    link_libs: &snap.link_libs,
+                    link_flags: &snap.link_flags,
+                    sketch_sources: &snap.sketch_sources,
+                    frameworks: vec!["arduino".to_string()],
+                    platform: "atmelavr",
+                    prog_path: build_result
+                        .firmware_path
+                        .as_deref()
+                        .or(build_result.elf_path.as_deref()),
+                    example_name: example_name.as_deref(),
+                };
+                if let Err(e) = crate::build_info::emit_build_info_for_orchestrator(inputs) {
+                    tracing::warn!("failed to emit build_info.json: {}", e);
+                }
+            }
+        }
+
         // 10. Persist fingerprint so the next warm invocation can hit the
         // fast path. Skip this for compile-db-only / symbol-analysis runs
         // — they don't produce the full artifact set the fast path