suggest workspace hints for boolean dependencies

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

@@ -787,12 +787,26 @@ 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 expected = format!("invalid type: boolean `{value}`, expected {expected}");
+                let err = if value {
+                    format!(
+                        "{expected}\n\
+                    note: if you meant to use a workspace member, you can write\n \
+                      dep.workspace = {value}"
+                    )
+                } else {
+                    expected
+                };
+
+                Err(serde_untagged::de::Error::custom(err))
+            })
             .map(|value| value.deserialize().map(TomlDependency::Detailed))
             .deserialize(deserializer)
     }

tests/testsuite/bad_config.rs

@@ -2641,6 +2641,41 @@ fn bad_dependency() {
         .run();
 }
 
+#[cargo_test]
+fn bad_dependency_true_literal() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.0.0"
+                edition = "2015"
+                authors = []
+
+                [dependencies]
+                bar = true
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("check")
+        .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
+ --> Cargo.toml:9:23
+  |
+9 |                 bar = true
+  |                       ^^^^
+  |
+
+"#]])
+        .run();
+}
+
 #[cargo_test]
 fn bad_debuginfo() {
     let p = project()