Helpful error when the [package] table is missing

Author: kornelski

src/cargo/util/toml/mod.rs

@@ -577,13 +577,40 @@ fn normalize_toml(
         normalized_toml.badges = original_toml.badges.clone();
     } else {
         if let Some(field) = original_toml.requires_package().next() {
-            bail!("this virtual manifest specifies a `{field}` section, which is not allowed");
+            return Err(field_requires_package_error(
+                field,
+                original_toml.workspace.is_some(),
+            ));
         }
     }
 
     Ok(normalized_toml)
 }
 
+fn field_requires_package_error(field: &str, has_workspace: bool) -> anyhow::Error {
+    let toml_brackets = if matches!(field, "bin" | "example" | "test" | "bench") {
+        ("[[", "]]")
+    } else {
+        ("[", "]")
+    };
+    let toml_table = format_args!("{}{field}{}", toml_brackets.0, toml_brackets.1);
+    let suggest_workspace = has_workspace
+        && matches!(
+            field,
+            "dependencies" | "dev-dependencies" | "build-dependencies" | "lints"
+        );
+    let help = if suggest_workspace {
+        format_args!(
+            "\nhelp: you can use `[workspace.{field}]` to define a template for workspace members to inherit from"
+        )
+    } else {
+        format_args!("")
+    };
+    anyhow!(
+        "this virtual manifest does not have a `[package]` section, which is required when specifying the `{toml_table}` section{help}"
+    )
+}
+
 fn normalize_patch<'a>(
     gctx: &GlobalContext,
     original_patch: Option<&BTreeMap<String, BTreeMap<PackageName, TomlDependency>>>,

tests/testsuite/workspaces.rs

@@ -2281,22 +2281,45 @@ fn ws_rustc_err() {
 }
 
 #[cargo_test]
-fn ws_err_unused() {
-    for table in &[
-        "[lib]",
-        "[[bin]]",
-        "[[example]]",
-        "[[test]]",
-        "[[bench]]",
-        "[dependencies]",
-        "[dev-dependencies]",
-        "[build-dependencies]",
-        "[features]",
-        "[target]",
-        "[badges]",
-        "[lints]",
-    ] {
-        let key = table.trim_start_matches('[').trim_end_matches(']');
+fn ws_err_unused_inheritable() {
+    ws_err_unused_inner(
+        &[
+            "[dependencies]",
+            "[dev-dependencies]",
+            "[build-dependencies]",
+            "[lints]",
+        ],
+        true,
+    );
+}
+
+#[cargo_test]
+fn ws_err_unused_package_only() {
+    ws_err_unused_inner(
+        &[
+            "[lib]",
+            "[[bin]]",
+            "[[example]]",
+            "[[test]]",
+            "[[bench]]",
+            "[features]",
+            "[target]",
+            "[badges]",
+        ],
+        false,
+    );
+}
+
+fn ws_err_unused_inner(tables: &[&str], expected_help: bool) {
+    for table in tables {
+        let expected_help = if expected_help {
+            format_args!(
+                "\n  [HELP] you can use `[workspace.{}]` to define a template for workspace members to inherit from",
+                table.trim_matches(['[', ']'])
+            )
+        } else {
+            format_args!("")
+        };
         let p = project()
             .file(
                 "Cargo.toml",
@@ -2319,7 +2342,7 @@ fn ws_err_unused() {
 [ERROR] failed to parse manifest at `[..]/foo/Cargo.toml`
 
 Caused by:
-  this virtual manifest specifies a `{key}` section, which is not allowed
+  this virtual manifest does not have a `[package]` section, which is required when specifying the `{table}` section{expected_help}
 ",
             ))
             .run();