fix(toml): Disallow inheriting of dependency public status

This is a step towards #44663.  When discussing inheriting this field
for rust-lang#13046, we realized that we should probably start by disallowing
inheritance.  We can always add it later.  imo the principle of what should
be inherited is what is truely common among dependencies.  For example,
we don't allow removing features.  Public should not be universally
applied and likely should be explicit so its not over-done, especially
since we can't (atm) lint for when a public dependency could be
non-public.

This reverts parts of rust-lang#12817

src/cargo/util/toml/mod.rs

@@ -120,6 +120,9 @@ fn read_manifest_from_str(
             if dep.is_optional() {
                 bail!("{name} is optional, but workspace dependencies cannot be optional",);
             }
+            if dep.is_public() {
+                bail!("{name} is public, but workspace dependencies cannot be public",);
+            }
         }
     }
     return if manifest.project.is_some() || manifest.package.is_some() {
@@ -1664,11 +1667,6 @@ fn inner_dependency_inherit_with<'a>(
                     }
                     _ => {}
                 }
-                // Inherit the workspace configuration for `public` unless
-                // it's explicitly specified for this dependency.
-                if let Some(public) = dependency.public {
-                    d.public = Some(public);
-                }
                 d.features = match (d.features.clone(), dependency.features.clone()) {
                     (Some(dep_feat), Some(inherit_feat)) => Some(
                         dep_feat

src/cargo/util_schemas/manifest.rs

@@ -534,6 +534,13 @@ impl TomlDependency {
         }
     }
 
+    pub fn is_public(&self) -> bool {
+        match self {
+            TomlDependency::Detailed(d) => d.public.unwrap_or(false),
+            TomlDependency::Simple(..) => false,
+        }
+    }
+
     pub fn unused_keys(&self) -> Vec<String> {
         match self {
             TomlDependency::Simple(_) => vec![],

src/doc/src/reference/unstable.md

@@ -304,6 +304,9 @@ my_dep = { version = "1.2.3", public = true }
 private_dep = "2.0.0" # Will be 'private' by default
 ```
 
+Documentation updates:
+- For workspace's "The `dependencies` table" section, include `public` as an unsupported field for `workspace.dependencies`
+
 ## msrv-policy
 - [#9930](https://github.com/rust-lang/cargo/issues/9930) (MSRV-aware resolver)
 - [#10653](https://github.com/rust-lang/cargo/issues/10653) (MSRV-aware cargo-add)

tests/testsuite/pub_priv.rs

@@ -199,7 +199,7 @@ Caused by:
 }
 
 #[cargo_test(nightly, reason = "exported_private_dependencies lint is unstable")]
-fn workspace_dep_made_public() {
+fn workspace_pub_disallowed() {
     Package::new("foo1", "0.1.0")
         .file("src/lib.rs", "pub struct FromFoo;")
         .publish();
@@ -244,5 +244,14 @@ fn workspace_dep_made_public() {
 
     p.cargo("check")
         .masquerade_as_nightly_cargo(&["public-dependency"])
+        .with_status(101)
+        .with_stderr(
+            "\
+error: failed to parse manifest at `[CWD]/Cargo.toml`
+
+Caused by:
+  foo2 is public, but workspace dependencies cannot be public
+",
+        )
         .run()
 }