Improve error context chaining

There are a bunch of occasions where we wrongly embed errors into a
string and report the resulting string as a new error. Fix them by
creating proper error chains.

Signed-off-by: Daniel Müller <[email protected]>

Author: d-e-s-o

examples/tc_port_whitelist/src/main.rs

@@ -1,6 +1,9 @@
+#![allow(clippy::let_unit_value)]
+
 use std::os::unix::io::AsFd as _;
 
 use anyhow::bail;
+use anyhow::Context as _;
 use anyhow::Result;
 
 use clap::Parser;
@@ -119,9 +122,11 @@ fn main() -> Result<()> {
         for (i, port) in opts.ports.iter().enumerate() {
             let key = (i as u32).to_ne_bytes();
             let val = port.to_ne_bytes();
-            if let Err(e) = skel.maps_mut().ports().update(&key, &val, MapFlags::ANY) {
-                bail!("Example limited to 10 ports: {e}");
-            }
+            let () = skel
+                .maps_mut()
+                .ports()
+                .update(&key, &val, MapFlags::ANY)
+                .context("Example limited to 10 ports")?;
         }
         ingress.create()?;
 

libbpf-cargo/src/gen/btf.rs

@@ -373,7 +373,7 @@ impl<'s> GenBtf<'s> {
                 }
                 Err(e) => {
                     if gen_impl_default || !t.is_struct {
-                        bail!("Could not construct a necessary Default Impl: {}", e);
+                        return Err(e.context("Could not construct a necessary Default Impl"));
                     }
                 }
             };

libbpf-cargo/src/gen/mod.rs

@@ -963,13 +963,12 @@ pub fn gen_single(
         ),
     };
 
-    if let Err(e) = gen_skel(debug, name, obj_file, output, rustfmt_path) {
-        bail!(
-            "Failed to generate skeleton for {}: {}",
+    let () = gen_skel(debug, name, obj_file, output, rustfmt_path).with_context(|| {
+        format!(
+            "Failed to generate skeleton for {}",
             obj_file.to_string_lossy(),
-            e
-        );
-    }
+        )
+    })?;
 
     Ok(())
 }
@@ -999,20 +998,19 @@ fn gen_project(
         let mut skel_path = obj.path.clone();
         skel_path.pop();
 
-        match gen_skel(
+        let () = gen_skel(
             debug,
             &obj.name,
             obj_file_path.as_path(),
             OutputDest::Directory(skel_path.as_path()),
             rustfmt_path,
-        ) {
-            Ok(_) => (),
-            Err(e) => bail!(
-                "Failed to generate skeleton for {}: {}",
-                obj.path.as_path().display(),
-                e
-            ),
-        }
+        )
+        .with_context(|| {
+            format!(
+                "Failed to generate skeleton for {}",
+                obj.path.as_path().display()
+            )
+        })?;
 
         match package_objs.get_mut(&obj.package) {
             Some(v) => v.push(obj.clone()),
@@ -1023,9 +1021,8 @@ fn gen_project(
     }
 
     for (package, objs) in package_objs {
-        if let Err(e) = gen_mods(&objs, rustfmt_path) {
-            bail!("Failed to generate mod.rs for package={}: {}", package, e);
-        }
+        let () = gen_mods(&objs, rustfmt_path)
+            .with_context(|| format!("Failed to generate mod.rs for package={package}"))?;
     }
 
     Ok(())

libbpf-cargo/src/lib.rs

@@ -55,6 +55,7 @@
 //! build`. This is a convenience command so you don't forget any steps. Alternatively, you could
 //! write a Makefile for your project.
 
+#![allow(clippy::let_unit_value)]
 #![warn(
     elided_lifetimes_in_paths,
     single_use_lifetimes,

libbpf-cargo/src/main.rs

@@ -1,3 +1,5 @@
+#![allow(clippy::let_unit_value)]
+
 use std::path::PathBuf;
 
 use anyhow::Result;

libbpf-cargo/src/metadata.rs

@@ -3,6 +3,7 @@ use std::path::Path;
 use std::path::PathBuf;
 
 use anyhow::bail;
+use anyhow::Context as _;
 use anyhow::Result;
 use cargo_metadata::MetadataCommand;
 use cargo_metadata::Package;
@@ -97,7 +98,7 @@ fn get_package(
                     );
                 }
             } else {
-                bail!(e);
+                return Err(e.into());
             }
         }
     };
@@ -148,11 +149,7 @@ pub fn get(debug: bool, manifest_path: Option<&PathBuf>) -> Result<(PathBuf, Vec
         cmd.manifest_path(path);
     }
 
-    let metadata = match cmd.exec() {
-        Ok(m) => m,
-        Err(e) => bail!("Failed to get cargo metadata: {}", e),
-    };
-
+    let metadata = cmd.exec().context("Failed to get cargo metadata")?;
     if metadata.workspace_members.is_empty() {
         bail!("Failed to find targets")
     }
@@ -162,10 +159,9 @@ pub fn get(debug: bool, manifest_path: Option<&PathBuf>) -> Result<(PathBuf, Vec
     for id in &metadata.workspace_members {
         for package in &metadata.packages {
             if id == &package.id {
-                match &mut get_package(debug, package, &target_directory) {
-                    Ok(vv) => v.append(vv),
-                    Err(e) => bail!("Failed to process package={}, error={}", package.name, e),
-                }
+                let vv = &mut get_package(debug, package, &target_directory)
+                    .with_context(|| format!("Failed to process package={}", package.name))?;
+                let () = v.append(vv);
             }
         }
     }