impl workspace hint for boolean dependencies

Author: borngraced

crates/cargo-util-schemas/src/manifest/mod.rs

@@ -776,12 +776,22 @@ impl<'de, P: Deserialize<'de> + Clone> de::Deserialize<'de> for TomlDependency<P
     where
         D: de::Deserializer<'de>,
     {
+        use serde::de::Error as _;
+        let expected = "a version string like \"0.9.8\" or a \
+                     detailed dependency like { version = \"0.9.8\" }";
         UntaggedEnumVisitor::new()
-            .expecting(
-                "a version string like \"0.9.8\" or a \
-                     detailed dependency like { version = \"0.9.8\" }",
-            )
+            .expecting(expected)
             .string(|value| Ok(TomlDependency::Simple(value.to_owned())))
+            .bool(|value| {
+                let err = format!(
+                    "invalid type: boolean `{value}`, expected {expected}\n\
+                    note: if you meant to use a workspace member, you can write\n \
+                      dep = {{ workspace = {value} }}\n\
+                    or\n \
+                      dep.workspace = {value}",
+                );
+                Err(serde_untagged::de::Error::custom(err))
+            })
             .map(|value| value.deserialize().map(TomlDependency::Detailed))
             .deserialize(deserializer)
     }

tests/testsuite/bad_config.rs

@@ -2670,6 +2670,10 @@ fn bad_boolean_dependency() {
         .with_status(101)
         .with_stderr_data(str![[r#"
 [ERROR] invalid type: boolean `true`, expected a version string like "0.9.8" or a detailed dependency like { version = "0.9.8" }
+[NOTE] if you meant to use a workspace member, you can write
+ dep = { workspace = true }
+or
+ dep.workspace = true
  --> Cargo.toml:9:23
   |
 9 |                 bar = true