From 2b2b675011ec6377d68f9466d8708080642b3903 Mon Sep 17 00:00:00 2001
From: Cole Helbling <cole.e.helbling@outlook.com>
Date: Fri, 3 Apr 2020 10:17:04 -0700
Subject: [PATCH 1/2] nixenv: describe what went wrong when io fails

Instead of just propagating a raw `std::io::Error`, wrap that in our own
`Error` enum to provide more context for what actually went wrong.
---
 ofborg/src/nixenv.rs | 54 +++++++++++++++++++++++++++++++++-----------
 1 file changed, 41 insertions(+), 13 deletions(-)

diff --git a/ofborg/src/nixenv.rs b/ofborg/src/nixenv.rs
index 80afa98..fc3753f 100644
--- a/ofborg/src/nixenv.rs
+++ b/ofborg/src/nixenv.rs
@@ -5,7 +5,7 @@ use crate::nixstats::EvaluationStats;
 use crate::outpathdiff;
 
 use std::fs::{self, File};
-use std::io::{BufRead, BufReader, Read, Seek, SeekFrom, Write};
+use std::io::{self, BufRead, BufReader, Read, Seek, SeekFrom, Write};
 use std::path::PathBuf;
 
 pub struct HydraNixEnv {
@@ -59,16 +59,32 @@ impl HydraNixEnv {
 
     /// Put outpaths.nix in to the project root, which is what
     /// emulates Hydra's behavior.
-    fn place_nix(&self) -> Result<(), std::io::Error> {
-        let mut file = File::create(self.outpath_nix_path())?;
-        file.write_all(include_bytes!("outpaths.nix"))?;
+    fn place_nix(&self) -> Result<(), Error> {
+        let outpath = self.outpath_nix_path();
 
-        Ok(())
+        let mut file = match File::create(&outpath) {
+            Ok(f) => f,
+            Err(e) => return Err(Error::CreateFile(outpath, e)),
+        };
+
+        match file.write_all(include_bytes!("outpaths.nix")) {
+            Ok(_) => Ok(()),
+            Err(e) => Err(Error::WriteFile(file, e)),
+        }
     }
 
-    fn remove_nix(&self) -> Result<(), std::io::Error> {
-        fs::remove_file(self.outpath_nix_path())?;
-        fs::remove_file(self.outpath_stats_path())?;
+    fn remove_nix(&self) -> Result<(), Error> {
+        let outpath_nix = self.outpath_nix_path();
+        let outpath_stats = self.outpath_stats_path();
+
+        if let Err(e) = fs::remove_file(&outpath_nix) {
+            return Err(Error::RemoveFile(outpath_nix, e));
+        }
+
+        if let Err(e) = fs::remove_file(&outpath_stats) {
+            return Err(Error::RemoveFile(outpath_stats, e));
+        }
+
         Ok(())
     }
 
@@ -80,7 +96,7 @@ impl HydraNixEnv {
         self.path.join(".gc-of-borg-stats.json")
     }
 
-    fn run_nix_env(&self) -> (bool, File, File, Result<File, std::io::Error>) {
+    fn run_nix_env(&self) -> (bool, File, File, Result<File, io::Error>) {
         let check_meta = if self.check_meta { "true" } else { "false" };
 
         let mut cmd = self.nix.safe_command(
@@ -106,14 +122,17 @@ impl HydraNixEnv {
 }
 
 pub enum Error {
-    Io(std::io::Error),
+    Io(io::Error),
+    CreateFile(PathBuf, io::Error),
+    RemoveFile(PathBuf, io::Error),
+    WriteFile(File, io::Error),
     CommandFailed(File),
-    StatsParse(File, Result<u64, std::io::Error>, serde_json::Error),
+    StatsParse(File, Result<u64, io::Error>, serde_json::Error),
     UncleanEvaluation(Vec<String>),
 }
 
-impl From<std::io::Error> for Error {
-    fn from(e: std::io::Error) -> Error {
+impl From<io::Error> for Error {
+    fn from(e: io::Error) -> Error {
         Error::Io(e)
     }
 }
@@ -122,6 +141,15 @@ impl Error {
     pub fn display(self) -> String {
         match self {
             Error::Io(e) => format!("Failed during the setup of executing nix-env: {:?}", e),
+            Error::CreateFile(path, err) => {
+                format!("Failed to create file '{:?}': {:?}", path, err)
+            }
+            Error::RemoveFile(path, err) => {
+                format!("Failed to remove file '{:?}': {:?}", path, err)
+            }
+            Error::WriteFile(file, err) => {
+                format!("Failed to write to file '{:?}': {:?}", file, err)
+            }
             Error::CommandFailed(mut fd) => {
                 let mut buffer = Vec::new();
                 let read_result = fd.read_to_end(&mut buffer);

From 9dc0fd123a6a01b10fc5ad140b31fb4d1d2a5feb Mon Sep 17 00:00:00 2001
From: Cole Helbling <cole.e.helbling@outlook.com>
Date: Fri, 3 Apr 2020 10:51:02 -0700
Subject: [PATCH 2/2] `match` -> `map_err`

---
 ofborg/src/nixenv.rs | 21 +++++----------------
 1 file changed, 5 insertions(+), 16 deletions(-)

diff --git a/ofborg/src/nixenv.rs b/ofborg/src/nixenv.rs
index fc3753f..756489c 100644
--- a/ofborg/src/nixenv.rs
+++ b/ofborg/src/nixenv.rs
@@ -61,29 +61,18 @@ impl HydraNixEnv {
     /// emulates Hydra's behavior.
     fn place_nix(&self) -> Result<(), Error> {
         let outpath = self.outpath_nix_path();
+        let mut file = File::create(&outpath).map_err(|e| Error::CreateFile(outpath, e))?;
 
-        let mut file = match File::create(&outpath) {
-            Ok(f) => f,
-            Err(e) => return Err(Error::CreateFile(outpath, e)),
-        };
-
-        match file.write_all(include_bytes!("outpaths.nix")) {
-            Ok(_) => Ok(()),
-            Err(e) => Err(Error::WriteFile(file, e)),
-        }
+        file.write_all(include_bytes!("outpaths.nix"))
+            .map_err(|e| Error::WriteFile(file, e))
     }
 
     fn remove_nix(&self) -> Result<(), Error> {
         let outpath_nix = self.outpath_nix_path();
         let outpath_stats = self.outpath_stats_path();
 
-        if let Err(e) = fs::remove_file(&outpath_nix) {
-            return Err(Error::RemoveFile(outpath_nix, e));
-        }
-
-        if let Err(e) = fs::remove_file(&outpath_stats) {
-            return Err(Error::RemoveFile(outpath_stats, e));
-        }
+        fs::remove_file(&outpath_nix).map_err(|e| Error::RemoveFile(outpath_nix, e))?;
+        fs::remove_file(&outpath_stats).map_err(|e| Error::RemoveFile(outpath_stats, e))?;
 
         Ok(())
     }