1 files changed, 272 insertions, 0 deletions

diff --git a/crates/ide_diagnostics/src/handlers/mismatched_arg_count.rs b/crates/ide_diagnostics/src/handlers/mismatched_arg_count.rs
new file mode 100644
index 000000000..a9b6d3870
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/mismatched_arg_count.rs
@@ -0,0 +1,272 @@
+use crate::{Diagnostic, DiagnosticsContext};
+
+// Diagnostic: mismatched-arg-count
+//
+// This diagnostic is triggered if a function is invoked with an incorrect amount of arguments.
+pub(crate) fn mismatched_arg_count(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::MismatchedArgCount,
+) -> Diagnostic {
+    let s = if d.expected == 1 { "" } else { "s" };
+    let message = format!("expected {} argument{}, found {}", d.expected, s, d.found);
+    Diagnostic::new(
+        "mismatched-arg-count",
+        message,
+        ctx.sema.diagnostics_display_range(d.call_expr.clone().map(|it| it.into())).range,
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::check_diagnostics;
+
+    #[test]
+    fn simple_free_fn_zero() {
+        check_diagnostics(
+            r#"
+fn zero() {}
+fn f() { zero(1); }
+       //^^^^^^^ error: expected 0 arguments, found 1
+"#,
+        );
+
+        check_diagnostics(
+            r#"
+fn zero() {}
+fn f() { zero(); }
+"#,
+        );
+    }
+
+    #[test]
+    fn simple_free_fn_one() {
+        check_diagnostics(
+            r#"
+fn one(arg: u8) {}
+fn f() { one(); }
+       //^^^^^ error: expected 1 argument, found 0
+"#,
+        );
+
+        check_diagnostics(
+            r#"
+fn one(arg: u8) {}
+fn f() { one(1); }
+"#,
+        );
+    }
+
+    #[test]
+    fn method_as_fn() {
+        check_diagnostics(
+            r#"
+struct S;
+impl S { fn method(&self) {} }
+
+fn f() {
+    S::method();
+} //^^^^^^^^^^^ error: expected 1 argument, found 0
+"#,
+        );
+
+        check_diagnostics(
+            r#"
+struct S;
+impl S { fn method(&self) {} }
+
+fn f() {
+    S::method(&S);
+    S.method();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn method_with_arg() {
+        check_diagnostics(
+            r#"
+struct S;
+impl S { fn method(&self, arg: u8) {} }
+
+            fn f() {
+                S.method();
+            } //^^^^^^^^^^ error: expected 1 argument, found 0
+            "#,
+        );
+
+        check_diagnostics(
+            r#"
+struct S;
+impl S { fn method(&self, arg: u8) {} }
+
+fn f() {
+    S::method(&S, 0);
+    S.method(1);
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn method_unknown_receiver() {
+        // note: this is incorrect code, so there might be errors on this in the
+        // future, but we shouldn't emit an argument count diagnostic here
+        check_diagnostics(
+            r#"
+trait Foo { fn method(&self, arg: usize) {} }
+
+fn f() {
+    let x;
+    x.method();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn tuple_struct() {
+        check_diagnostics(
+            r#"
+struct Tup(u8, u16);
+fn f() {
+    Tup(0);
+} //^^^^^^ error: expected 2 arguments, found 1
+"#,
+        )
+    }
+
+    #[test]
+    fn enum_variant() {
+        check_diagnostics(
+            r#"
+enum En { Variant(u8, u16), }
+fn f() {
+    En::Variant(0);
+} //^^^^^^^^^^^^^^ error: expected 2 arguments, found 1
+"#,
+        )
+    }
+
+    #[test]
+    fn enum_variant_type_macro() {
+        check_diagnostics(
+            r#"
+macro_rules! Type {
+    () => { u32 };
+}
+enum Foo {
+    Bar(Type![])
+}
+impl Foo {
+    fn new() {
+        Foo::Bar(0);
+        Foo::Bar(0, 1);
+      //^^^^^^^^^^^^^^ error: expected 1 argument, found 2
+        Foo::Bar();
+      //^^^^^^^^^^ error: expected 1 argument, found 0
+    }
+}
+        "#,
+        );
+    }
+
+    #[test]
+    fn varargs() {
+        check_diagnostics(
+            r#"
+extern "C" {
+    fn fixed(fixed: u8);
+    fn varargs(fixed: u8, ...);
+    fn varargs2(...);
+}
+
+fn f() {
+    unsafe {
+        fixed(0);
+        fixed(0, 1);
+      //^^^^^^^^^^^ error: expected 1 argument, found 2
+        varargs(0);
+        varargs(0, 1);
+        varargs2();
+        varargs2(0);
+        varargs2(0, 1);
+    }
+}
+        "#,
+        )
+    }
+
+    #[test]
+    fn arg_count_lambda() {
+        check_diagnostics(
+            r#"
+fn main() {
+    let f = |()| ();
+    f();
+  //^^^ error: expected 1 argument, found 0
+    f(());
+    f((), ());
+  //^^^^^^^^^ error: expected 1 argument, found 2
+}
+"#,
+        )
+    }
+
+    #[test]
+    fn cfgd_out_call_arguments() {
+        check_diagnostics(
+            r#"
+struct C(#[cfg(FALSE)] ());
+impl C {
+    fn new() -> Self {
+        Self(
+            #[cfg(FALSE)]
+            (),
+        )
+    }
+
+    fn method(&self) {}
+}
+
+fn main() {
+    C::new().method(#[cfg(FALSE)] 0);
+}
+            "#,
+        );
+    }
+
+    #[test]
+    fn cfgd_out_fn_params() {
+        check_diagnostics(
+            r#"
+fn foo(#[cfg(NEVER)] x: ()) {}
+
+struct S;
+
+impl S {
+    fn method(#[cfg(NEVER)] self) {}
+    fn method2(#[cfg(NEVER)] self, arg: u8) {}
+    fn method3(self, #[cfg(NEVER)] arg: u8) {}
+}
+
+extern "C" {
+    fn fixed(fixed: u8, #[cfg(NEVER)] ...);
+    fn varargs(#[cfg(not(NEVER))] ...);
+}
+
+fn main() {
+    foo();
+    S::method();
+    S::method2(0);
+    S::method3(S);
+    S.method3();
+    unsafe {
+        fixed(0);
+        varargs(1, 2, 3);
+    }
+}
+            "#,
+        )
+    }
+}