[x-lint] better error messages for IO errors

Make errors easier to diagnose. Closes: diem#3487 Approved by: bmwill
yuan-xy · Apr 20, 2020 · aa588d4 · aa588d4
1 parent df84bf7
commit aa588d4
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Showing 3 changed files with 20 additions and 12 deletions.
diff --git a/devtools/x-lint/src/errors.rs b/devtools/x-lint/src/errors.rs
@@ -1,7 +1,7 @@
 // Copyright (c) The Libra Core Contributors
 // SPDX-License-Identifier: Apache-2.0
 
-use std::{error, fmt, io, process::ExitStatus, result};
+use std::{borrow::Cow, error, fmt, io, process::ExitStatus, result};
 
 /// Type alias for the return type for `run` methods.
 pub type Result<T, E = SystemError> = result::Result<T, E>;
@@ -15,7 +15,19 @@ pub enum SystemError {
         status: ExitStatus,
     },
     Guppy(guppy::Error),
-    Io(io::Error),
+    Io {
+        context: Cow<'static, str>,
+        err: io::Error,
+    },
+}
+
+impl SystemError {
+    pub fn io(context: impl Into<Cow<'static, str>>, err: io::Error) -> Self {
+        SystemError::Io {
+            context: context.into(),
+            err,
+        }
+    }
 }
 
 impl fmt::Display for SystemError {
@@ -25,7 +37,7 @@ impl fmt::Display for SystemError {
                 Some(code) => write!(f, "'{}' failed with exit code {}", cmd, code),
                 None => write!(f, "'{}' terminated by signal", cmd),
             },
-            SystemError::Io(err) => write!(f, "IO error: {}", err),
+            SystemError::Io { context, .. } => write!(f, "while {}", context),
             SystemError::Guppy(err) => write!(f, "guppy error: {}", err),
         }
     }
@@ -35,7 +47,7 @@ impl error::Error for SystemError {
     fn source(&self) -> Option<&(dyn error::Error + 'static)> {
         match self {
             SystemError::Exec { .. } => None,
-            SystemError::Io(err) => Some(err),
+            SystemError::Io { err, .. } => Some(err),
             SystemError::Guppy(err) => Some(err),
         }
     }
@@ -46,9 +58,3 @@ impl From<guppy::Error> for SystemError {
         SystemError::Guppy(err)
     }
 }
-
-impl From<io::Error> for SystemError {
-    fn from(err: io::Error) -> Self {
-        SystemError::Io(err)
-    }
-}
diff --git a/devtools/x-lint/src/file.rs b/devtools/x-lint/src/file.rs
@@ -40,7 +40,8 @@ impl<'l> FileContext<'l> {
     /// `pub(super)` is to dissuade individual linters from loading file contexts.
     pub(super) fn load(self) -> Result<ContentContext<'l>> {
         let full_path = self.project_ctx.full_path(self.file_path);
-        let content = fs::read(&full_path)?;
+        let content = fs::read(&full_path)
+            .map_err(|err| SystemError::io(format!("loading {}", full_path.display()), err))?;
         Ok(ContentContext::new(self, content))
     }
 }

diff --git a/devtools/x-lint/src/runner.rs b/devtools/x-lint/src/runner.rs
@@ -244,7 +244,8 @@ impl<'cfg> LintEngine<'cfg> {
                     // The -z causes files to not be quoted, and to be separated by \0.
                     .args(&["ls-files", "-z"])
                     .stderr(Stdio::inherit())
-                    .output()?;
+                    .output()
+                    .map_err(|err| SystemError::io("running git ls-files", err))?;
                 if !output.status.success() {
                     return Err(SystemError::Exec {
                         cmd: "git ls-files",