Add configuration option to allow unreachable! in test functions

Author: AMS21

clippy_config/src/conf.rs

@@ -403,6 +403,9 @@ define_Conf! {
     #[lints(renamed_function_params)]
     allow_renamed_params_for: Vec<String> =
         DEFAULT_ALLOWED_TRAITS_WITH_RENAMED_PARAMS.iter().map(ToString::to_string).collect(),
+    /// Whether `unreachable` should be allowed in test functions or `#[cfg(test)]`
+    #[lints(unreachable)]
+    allow_unreachable_in_tests: bool = false,
     /// Whether `unwrap` should be allowed in code always evaluated at compile time
     #[lints(unwrap_used)]
     allow_unwrap_in_consts: bool = true,

clippy_lints/src/panic_unimplemented.rs

@@ -10,12 +10,14 @@ use rustc_span::sym;
 
 pub struct PanicUnimplemented {
     allow_panic_in_tests: bool,
+    allow_unreachable_in_tests: bool,
 }
 
 impl PanicUnimplemented {
     pub fn new(conf: &'static Conf) -> Self {
         Self {
             allow_panic_in_tests: conf.allow_panic_in_tests,
+            allow_unreachable_in_tests: conf.allow_unreachable_in_tests,
         }
     }
 }
@@ -131,6 +133,10 @@ impl<'tcx> LateLintPass<'tcx> for PanicUnimplemented {
                     );
                 },
                 Some(sym::unreachable_macro) => {
+                    if self.allow_unreachable_in_tests && is_in_test(cx.tcx, expr.hir_id) {
+                        return;
+                    }
+
                     span_lint(cx, UNREACHABLE, macro_call.span, "usage of the `unreachable!` macro");
                 },
                 _ => {},

tests/ui-toml/unreachable/clippy.toml

@@ -0,0 +1 @@
+allow-unreachable-in-tests = true

tests/ui-toml/unreachable/unreachable.rs

@@ -0,0 +1,25 @@
+//@compile-flags: --test
+#![warn(clippy::unreachable)]
+
+fn main() {
+    unreachable!();
+    //~^ unreachable
+}
+
+#[test]
+fn allowed_in_test_fn() {
+    unreachable!();
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn nested_test() {
+        unreachable!();
+    }
+
+    fn helper() {
+        // still test context should be allowed
+        unreachable!();
+    }
+}

tests/ui-toml/unreachable/unreachable.stderr

@@ -0,0 +1,11 @@
+error: usage of the `unreachable!` macro
+  --> tests/ui-toml/unreachable/unreachable.rs:5:5
+   |
+LL |     unreachable!();
+   |     ^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::unreachable` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::unreachable)]`
+
+error: aborting due to 1 previous error
+