1 files changed, 121 insertions, 0 deletions
diff --git a/src/tools/clippy/tests/ui/missing_const_for_fn/cant_be_const.rs b/src/tools/clippy/tests/ui/missing_const_for_fn/cant_be_const.rs
new file mode 100644
index 000000000..aa60d0504
--- /dev/null
+++ b/src/tools/clippy/tests/ui/missing_const_for_fn/cant_be_const.rs
@@ -0,0 +1,121 @@
+//! False-positive tests to ensure we don't suggest `const` for things where it would cause a
+//! compilation error.
+//! The .stderr output of this test should be empty. Otherwise it's a bug somewhere.
+
+// aux-build:helper.rs
+
+#![warn(clippy::missing_const_for_fn)]
+#![feature(start)]
+#![feature(custom_inner_attributes)]
+
+extern crate helper;
+
+struct Game;
+
+// This should not be linted because it's already const
+const fn already_const() -> i32 {
+    32
+}
+
+impl Game {
+    // This should not be linted because it's already const
+    pub const fn already_const() -> i32 {
+        32
+    }
+}
+
+// Allowing on this function, because it would lint, which we don't want in this case.
+#[allow(clippy::missing_const_for_fn)]
+fn random() -> u32 {
+    42
+}
+
+// We should not suggest to make this function `const` because `random()` is non-const
+fn random_caller() -> u32 {
+    random()
+}
+
+static Y: u32 = 0;
+
+// We should not suggest to make this function `const` because const functions are not allowed to
+// refer to a static variable
+fn get_y() -> u32 {
+    Y
+    //~^ ERROR E0013
+}
+
+// Don't lint entrypoint functions
+#[start]
+fn init(num: isize, something: *const *const u8) -> isize {
+    1
+}
+
+trait Foo {
+    // This should not be suggested to be made const
+    // (rustc doesn't allow const trait methods)
+    fn f() -> u32;
+
+    // This should not be suggested to be made const either
+    fn g() -> u32 {
+        33
+    }
+}
+
+// Don't lint in external macros (derive)
+#[derive(PartialEq, Eq)]
+struct Point(isize, isize);
+
+impl std::ops::Add for Point {
+    type Output = Self;
+
+    // Don't lint in trait impls of derived methods
+    fn add(self, other: Self) -> Self {
+        Point(self.0 + other.0, self.1 + other.1)
+    }
+}
+
+mod with_drop {
+    pub struct A;
+    pub struct B;
+    impl Drop for A {
+        fn drop(&mut self) {}
+    }
+
+    impl A {
+        // This can not be const because the type implements `Drop`.
+        pub fn b(self) -> B {
+            B
+        }
+    }
+
+    impl B {
+        // This can not be const because `a` implements `Drop`.
+        pub fn a(self, a: A) -> B {
+            B
+        }
+    }
+}
+
+fn const_generic_params<T, const N: usize>(t: &[T; N]) -> &[T; N] {
+    t
+}
+
+fn const_generic_return<T, const N: usize>(t: &[T]) -> &[T; N] {
+    let p = t.as_ptr() as *const [T; N];
+
+    unsafe { &*p }
+}
+
+// Do not lint this because it calls a function whose constness is unstable.
+fn unstably_const_fn() {
+    helper::unstably_const_fn()
+}
+
+mod const_fn_stabilized_after_msrv {
+    #![clippy::msrv = "1.46.0"]
+
+    // Do not lint this because `u8::is_ascii_digit` is stabilized as a const function in 1.47.0.
+    fn const_fn_stabilized_after_msrv(byte: u8) {
+        byte.is_ascii_digit();
+    }
+}