Add error context

Summary: When file writing fails, attach some context in the error message.

Reviewed By: jknoxville

Differential Revision: D21400273

fbshipit-source-id: f7cce5446ec27d5eb38f1902f24c61169dd644ac

packer/src/main.rs

@@ -8,7 +8,7 @@
 mod error;
 mod types;
 
-use anyhow::{bail, Result};
+use anyhow::{bail, Context, Result};
 use clap::value_t_or_exit;
 use std::collections::BTreeMap;
 use std::fs::File;
@@ -50,7 +50,12 @@ fn pack(
             );
             let _ = stdout().flush();
             let output_path = path::Path::new(output_directory).join(format!("{}.tar", pack_type));
-            let mut tar = tar::Builder::new(File::create(&output_path)?);
+            let mut tar = tar::Builder::new(File::create(&output_path).with_context(|| {
+                format!(
+                    "Couldn't open file for writing: {}",
+                    &output_path.to_string_lossy()
+                )
+            })?);
             // MacOS uses symlinks for bundling multiple framework versions and pointing
             // to the "Current" one.
             tar.follow_symlinks(false);
@@ -143,6 +148,12 @@ fn main() -> Result<(), anyhow::Error> {
         serde_yaml::from_str(&pack_list_str).expect("Failed to deserialize YAML packlist.");
     let output_directory =
         &path::PathBuf::from(args.value_of("output").expect("argument has default"));
+    std::fs::create_dir_all(output_directory).with_context(|| {
+        format!(
+            "Failed to create output directory '{}'.",
+            output_directory.to_string_lossy()
+        )
+    })?;
     let archive_paths = pack(&platform, &dist_dir, &pack_list, output_directory)?;
     manifest(&archive_paths, &output_directory)?;
 
@@ -166,7 +177,8 @@ fn write_manifest(
     archive_manifest: &PackManifest,
 ) -> Result<path::PathBuf> {
     let path = path::PathBuf::from(output_directory).join("manifest.json");
-    let mut file = File::create(&path)?;
+    let mut file = File::create(&path)
+        .with_context(|| format!("Failed to write manifest to {}", &path.to_string_lossy()))?;
     file.write_all(&serde_json::to_string_pretty(archive_manifest)?.as_bytes())?;
     Ok(path)
 }