Add some more context to errors walking path sources.

Author: ehuss

src/cargo/core/compiler/fingerprint.rs

@@ -1209,7 +1209,12 @@ fn calculate_normal(cx: &mut Context<'_, '_>, unit: &Unit) -> CargoResult<Finger
     let target_root = target_root(cx);
     let local = if unit.mode.is_doc() {
         // rustdoc does not have dep-info files.
-        let fingerprint = pkg_fingerprint(cx.bcx, &unit.pkg)?;
+        let fingerprint = pkg_fingerprint(cx.bcx, &unit.pkg).chain_err(|| {
+            format!(
+                "failed to determine package fingerprint for documenting {}",
+                unit.pkg
+            )
+        })?;
         vec![LocalFingerprint::Precalculated(fingerprint)]
     } else {
         let dep_info = dep_info_loc(cx, unit);
@@ -1270,7 +1275,18 @@ fn calculate_run_custom_build(cx: &mut Context<'_, '_>, unit: &Unit) -> CargoRes
     // the whole crate.
     let (gen_local, overridden) = build_script_local_fingerprints(cx, unit);
     let deps = &cx.build_explicit_deps[unit];
-    let local = (gen_local)(deps, Some(&|| pkg_fingerprint(cx.bcx, &unit.pkg)))?.unwrap();
+    let local = (gen_local)(
+        deps,
+        Some(&|| {
+            pkg_fingerprint(cx.bcx, &unit.pkg).chain_err(|| {
+                format!(
+                    "failed to determine package fingerprint for build script for {}",
+                    unit.pkg
+                )
+            })
+        }),
+    )?
+    .unwrap();
     let output = deps.build_script_output.clone();
 
     // Include any dependencies of our execution, which is typically just the

src/cargo/sources/path.rs

@@ -96,6 +96,15 @@ impl<'cfg> PathSource<'cfg> {
     /// are relevant for building this package, but it also contains logic to
     /// use other methods like .gitignore to filter the list of files.
     pub fn list_files(&self, pkg: &Package) -> CargoResult<Vec<PathBuf>> {
+        self._list_files(pkg).chain_err(|| {
+            format!(
+                "failed to determine list of files in {}",
+                pkg.root().display()
+            )
+        })
+    }
+
+    fn _list_files(&self, pkg: &Package) -> CargoResult<Vec<PathBuf>> {
         let root = pkg.root();
         let no_include_option = pkg.manifest().include().is_empty();
 
@@ -415,7 +424,12 @@ impl<'cfg> PathSource<'cfg> {
 
         let mut max = FileTime::zero();
         let mut max_path = PathBuf::new();
-        for file in self.list_files(pkg)? {
+        for file in self.list_files(pkg).chain_err(|| {
+            format!(
+                "failed to determine the most recently modified file in {}",
+                pkg.root().display()
+            )
+        })? {
             // An `fs::stat` error here is either because path is a
             // broken symlink, a permissions error, or a race
             // condition where this path was `rm`-ed -- either way,

tests/testsuite/build_script.rs

@@ -3985,12 +3985,21 @@ fn build_script_scan_eacces() {
         .build();
     let path = p.root().join("secrets");
     fs::set_permissions(&path, fs::Permissions::from_mode(0)).unwrap();
-    // "Caused by" is a string from libc such as the following:
+    // The last "Caused by" is a string from libc such as the following:
     //   Permission denied (os error 13)
     p.cargo("build")
         .with_stderr(
             "\
-[ERROR] cannot read \"[..]/foo/secrets\"
+[ERROR] failed to determine package fingerprint for build script for foo v0.0.1 ([..]/foo)
+
+Caused by:
+  failed to determine the most recently modified file in [..]/foo
+
+Caused by:
+  failed to determine list of files in [..]/foo
+
+Caused by:
+  cannot read \"[..]/foo/secrets\"
 
 Caused by:
   [..]