WIP: wrote 3 tests about improving the error message in the path dependency

src/cargo/core/resolver/errors.rs

@@ -1,10 +1,11 @@
 use std::fmt;
 use std::fmt::Write as _;
+use std::path::Path;
 use std::task::Poll;
 
-use crate::core::{Dependency, PackageId, Registry, Summary};
-use crate::sources::IndexSummary;
+use crate::core::{Dependency, PackageId, Registry, SourceId, Summary};
 use crate::sources::source::QueryKind;
+use crate::sources::{IndexSummary, PathSource, RecursivePathSource};
 use crate::util::edit_distance::{closest, edit_distance};
 use crate::util::errors::CargoResult;
 use crate::util::{GlobalContext, OptVersionReq, VersionExt};
@@ -385,6 +386,14 @@ pub(super) fn activation_error(
                 });
         let _ = writeln!(&mut msg, "perhaps you meant:      {suggestions}");
     } else {
+        let sid = dep.source_id();
+        let path = dep.source_id().url().to_file_path().unwrap();
+
+        if let Some(gctx) = gctx {
+            debug_source_path(&mut msg, &path.as_path(), &gctx, sid);
+            debug_recursive_source(&mut msg, &path.as_path(), &gctx, sid);
+        }
+
         let _ = writeln!(
             &mut msg,
             "no matching package named `{}` found",
@@ -568,3 +577,49 @@ pub(crate) fn describe_path<'a>(
 
     String::new()
 }
+
+fn inspect_root_package(msg: &mut String, path: &Path, gctx: &GlobalContext, sid: SourceId) {
+    let mut ps = PathSource::new(path, sid, gctx);
+
+    if let Err(e) = ps.root_package() {
+        msg.push_str(&e.to_string());
+        msg.push('\n');
+        return;
+    }
+
+    if let Err(e) = ps.load() {
+        msg.push_str(&e.to_string());
+        msg.push('\n');
+        return;
+    }
+
+    if let Err(e) = ps.read_package() {
+        msg.push_str(&e.to_string());
+        msg.push('\n');
+    }
+}
+
+fn inspect_recursive_packages(msg: &mut String, path: &Path, gctx: &GlobalContext, sid: SourceId) {
+    let mut rps = RecursivePathSource::new(path, sid, gctx);
+
+    if let Err(e) = rps.load() {
+        msg.push_str(&e.to_string());
+        msg.push('\n');
+        return;
+    }
+
+    match rps.read_packages() {
+        Ok(pkgs) => {
+            for p in pkgs {
+                if let Err(e) = rps.list_files(&p) {
+                    msg.push_str(&e.to_string());
+                    msg.push('\n');
+                }
+            }
+        }
+        Err(e) => {
+            msg.push_str(&e.to_string());
+            msg.push('\n');
+        }
+    }
+}

src/cargo/sources/path.rs

@@ -123,7 +123,7 @@ impl<'gctx> PathSource<'gctx> {
         Ok(())
     }
 
-    fn read_package(&self) -> CargoResult<Package> {
+    pub fn read_package(&self) -> CargoResult<Package> {
         let path = self.path.join("Cargo.toml");
         let pkg = ops::read_package(&path, self.source_id, self.gctx)?;
         Ok(pkg)

tests/testsuite/path.rs

@@ -1919,3 +1919,151 @@ foo v1.0.0 ([ROOT]/foo)
 "#]])
         .run();
 }
+
+#[cargo_test]
+fn invalid_package_name_in_path() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.5.0"
+            edition = "2015"
+            authors = []
+
+            [workspace]
+
+            [dependencies]
+            definitely_not_bar = { path = "crates/bar" }
+        "#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            "crates/bar/Cargo.toml",
+            r#"
+            [package]
+            name = "bar"
+            version = "0.5.0"
+            edition = "2015"
+            authors = []
+            "#,
+        )
+        .file("crates/bar/src/lib.rs", "")
+        .build();
+
+    p.cargo("generate-lockfile")
+        .with_status(101)
+        .with_stderr_data(str![[r#"
+[ERROR] no matching package named `definitely_not_bar` found
+location searched: [ROOT]/foo/crates/bar
+required by package `foo v0.5.0 ([ROOT]/foo)`
+
+"#]])
+        .run();
+}
+
+#[cargo_test]
+fn invalid_package_in_subdirectory() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.5.0"
+            edition = "2015"
+            authors = []
+
+            [workspace]
+
+            [dependencies]
+            definitely_not_bar = { path = "crates/bar" }
+        "#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            "crates/bar/definitely_not_bar/Cargo.toml",
+            r#"
+            [package]
+            name = "definitely_not_bar"
+            version = "0.5.0"
+            edition = "2015"
+            authors = []
+            "#,
+        )
+        .file("crates/bar/definitely_not_bar/src/lib.rs", "")
+        .build();
+
+    p.cargo("generate-lockfile")
+        .with_status(101)
+        .with_stderr_data(str![[r#"
+[ERROR] failed to load manifest for dependency `definitely_not_bar`
+
+Caused by:
+  failed to read `[ROOT]/foo/crates/bar/Cargo.toml`
+
+Caused by:
+  [NOT_FOUND]
+
+"#]])
+        .run();
+}
+
+#[cargo_test]
+fn invalid_manifest_in_path() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.5.0"
+            edition = "2015"
+            authors = []
+
+            [workspace]
+
+            [dependencies]
+            definitely_not_bar = { path = "crates/bar" }
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            "crates/bar/alice/Cargo.toml",
+            r#"
+            [package]
+            name = "alice"
+            version = "0.5.0"
+            edition = "2015"
+            authors = []
+        "#,
+        )
+        .file("crates/bar/alice/src/lib.rs", "")
+        .file(
+            "crates/bar/bob/Cargo.toml",
+            r#"
+            [package]
+            name = "bob"
+            version = "0.5.0"
+            edition = "2015"
+            authors = []
+        "#,
+        )
+        .file("crates/bar/bob/src/lib.rs", "")
+        .build();
+
+    p.cargo("generate-lockfile")
+        .with_status(101)
+        .with_stderr_data(str![[r#"
+[ERROR] failed to load manifest for dependency `definitely_not_bar`
+
+Caused by:
+  failed to read `[ROOT]/foo/crates/bar/Cargo.toml`
+
+Caused by:
+  [NOT_FOUND]
+
+"#]])
+        .run();
+}