fix(cargo-lints): Respect Forbid lint level

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

@@ -1506,7 +1506,7 @@ pub struct TomlLintConfig {
     pub priority: i8,
 }
 
-#[derive(Serialize, Deserialize, Debug, Copy, Clone)]
+#[derive(Serialize, Deserialize, Debug, Copy, Clone, Eq, PartialEq)]
 #[serde(rename_all = "kebab-case")]
 pub enum TomlLintLevel {
     Forbid,

src/cargo/util/lints.rs

@@ -68,6 +68,13 @@ pub struct LintGroup {
     pub edition_lint_opts: Option<(Edition, LintLevel)>,
 }
 
+const TEST_DUMMY_UNSTABLE: LintGroup = LintGroup {
+    name: "test_dummy_unstable",
+    desc: "test_dummy_unstable is meant to only be used in tests",
+    default_level: LintLevel::Allow,
+    edition_lint_opts: None,
+};
+
 #[derive(Copy, Clone, Debug)]
 pub struct Lint {
     pub name: &'static str,
@@ -79,23 +86,37 @@ pub struct Lint {
 
 impl Lint {
     pub fn level(&self, lints: &TomlToolLints, edition: Edition) -> LintLevel {
+        let edition_level = self
+            .edition_lint_opts
+            .filter(|(e, _)| edition >= *e)
+            .map(|(_, l)| l);
+
+        if self.default_level == LintLevel::Forbid || edition_level == Some(LintLevel::Forbid) {
+            return LintLevel::Forbid;
+        }
+
         let level = self
             .groups
             .iter()
             .map(|g| g.name)
             .chain(std::iter::once(self.name))
             .filter_map(|n| lints.get(n).map(|l| (n, l)))
-            .max_by_key(|(n, l)| (l.priority(), std::cmp::Reverse(*n)));
+            .max_by_key(|(n, l)| {
+                (
+                    l.level() == TomlLintLevel::Forbid,
+                    l.priority(),
+                    std::cmp::Reverse(*n),
+                )
+            });
 
         match level {
             Some((_, toml_lint)) => toml_lint.level().into(),
             None => {
-                if let Some((lint_edition, lint_level)) = self.edition_lint_opts {
-                    if edition >= lint_edition {
-                        return lint_level;
-                    }
+                if let Some(level) = edition_level {
+                    level
+                } else {
+                    self.default_level
                 }
-                self.default_level
             }
         }
     }
@@ -145,7 +166,7 @@ impl From<TomlLintLevel> for LintLevel {
 const IM_A_TEAPOT: Lint = Lint {
     name: "im_a_teapot",
     desc: "`im_a_teapot` is specified",
-    groups: &[],
+    groups: &[TEST_DUMMY_UNSTABLE],
     default_level: LintLevel::Allow,
     edition_lint_opts: None,
 };

tests/testsuite/lints_table.rs

@@ -899,3 +899,43 @@ warning: `im_a_teapot` is specified
         )
         .run();
 }
+
+#[cargo_test]
+fn forbid_not_overridden() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+cargo-features = ["test-dummy-unstable"]
+
+[package]
+name = "foo"
+version = "0.0.1"
+edition = "2015"
+authors = []
+im-a-teapot = true
+
+[lints.cargo]
+im-a-teapot = { level = "warn", priority = 10 }
+test-dummy-unstable = { level = "forbid", priority = -1 }
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("check -Zcargo-lints")
+        .masquerade_as_nightly_cargo(&["cargo-lints", "test-dummy-unstable"])
+        .with_status(101)
+        .with_stderr(
+            "\
+error: `im_a_teapot` is specified
+ --> Cargo.toml:9:1
+  |
+9 | im-a-teapot = true
+  | ^^^^^^^^^^^^^^^^^^
+  |
+  = note: `cargo::im_a_teapot` is set to `forbid`
+",
+        )
+        .run();
+}