incompatible_msrv: lint function calls with any argument count

The lint for function calls was previously restricted to functions taking
exactly one argument. This was not documented.

Generalizing the lint to an arbitrary number of arguments in the function
call requires special casing some macro expansions from the standard
library. Macros such as `panic!()` or `assert_eq!()` exist since Rust
1.0.0, but modern stdlib expand those macros into calls to functions
introduced in later Rust versions. While it is desirable to lint code
inside macros, using MSRV-incompatible functions coming from `core`
in macro expansions has been special-cased to not trigger this lint.

Also, code coming from compiler desugaring may contain function calls
(for example, `a..=b` is now desugared into `RangeInclusive::new(a,
b)`. Those should not be linted either as the compiler is allowed to
use unstable function calls.

Author: samueltardieu

clippy_lints/src/incompatible_msrv.rs

@@ -4,12 +4,12 @@ use clippy_utils::is_in_test;
 use clippy_utils::msrvs::Msrv;
 use rustc_attr_parsing::{RustcVersion, StabilityLevel, StableSince};
 use rustc_data_structures::fx::FxHashMap;
-use rustc_hir::{Expr, ExprKind, HirId};
+use rustc_hir::{Expr, ExprKind, HirId, QPath};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::impl_lint_pass;
 use rustc_span::def_id::DefId;
-use rustc_span::{ExpnKind, Span};
+use rustc_span::{ExpnKind, Span, sym};
 
 declare_clippy_lint! {
     /// ### What it does
@@ -95,6 +95,19 @@ impl IncompatibleMsrv {
             // Intentionally not using `.from_expansion()`, since we do still care about macro expansions
             return;
         }
+        // Functions coming from `core` while expanding a macro such as `assert*!()` get to cheat too: the
+        // macros may have existed prior to the checked MSRV, but their expansion with a recent compiler
+        // might use recent functions or methods. Compiling with an older compiler would not use those.
+        if span.from_expansion()
+            && cx.tcx.crate_name(def_id.krate) == sym::core
+            && span
+                .ctxt()
+                .outer_expn_data()
+                .macro_def_id
+                .is_some_and(|def_id| cx.tcx.crate_name(def_id.krate) == sym::core)
+        {
+            return;
+        }
         self.emit_lint_for(cx, span, version);
     }
 
@@ -125,8 +138,11 @@ impl<'tcx> LateLintPass<'tcx> for IncompatibleMsrv {
                     self.emit_lint_if_under_msrv(cx, method_did, expr.hir_id, span);
                 }
             },
-            ExprKind::Call(call, [_]) => {
-                if let ExprKind::Path(qpath) = call.kind
+            ExprKind::Call(call, _) => {
+                // Desugaring into function calls by the compiler will use `QPath::LangItem` variants. Those should
+                // not be linted as they will not be generated in older compilers if the function is not available,
+                // and the compiler is allowed to call unstable functions.
+                if let ExprKind::Path(qpath @ (QPath::Resolved(..) | QPath::TypeRelative(..))) = call.kind
                     && let Some(path_def_id) = cx.qpath_res(&qpath, call.hir_id).opt_def_id()
                 {
                     self.emit_lint_if_under_msrv(cx, path_def_id, expr.hir_id, call.span);

tests/ui/incompatible_msrv.rs

@@ -1,5 +1,6 @@
 #![warn(clippy::incompatible_msrv)]
 #![feature(custom_inner_attributes)]
+#![feature(panic_internals)]
 #![clippy::msrv = "1.3.0"]
 
 use std::collections::HashMap;
@@ -33,4 +34,42 @@ async fn issue12273(v: impl Future<Output = ()>) {
     v.await;
 }
 
+fn core_special_treatment(p: bool) {
+    // Do not lint code coming from `core` macros expanding into `core` function calls
+    if p {
+        panic!("foo"); // Do not lint
+    }
+
+    // But still lint code calling `core` functions directly
+    if p {
+        core::panicking::panic("foo");
+        //~^ ERROR: is `1.3.0` but this item is stable since `1.6.0`
+    }
+
+    // Lint code calling `core` from non-`core` macros
+    macro_rules! my_panic {
+        ($msg:expr) => {
+            core::panicking::panic($msg)
+        }; //~^ ERROR: is `1.3.0` but this item is stable since `1.6.0`
+    }
+    my_panic!("foo");
+
+    // Lint even when the macro comes from `core` and calls `core` functions
+    assert!(core::panicking::panic("out of luck"));
+    //~^ ERROR: is `1.3.0` but this item is stable since `1.6.0`
+}
+
+#[clippy::msrv = "1.26.0"]
+fn lang_items() {
+    // Do not lint lang items. `..=` will expand into `RangeInclusive::new()`, which was introduced
+    // in Rust 1.27.0.
+    let _ = 1..=3;
+}
+
+#[clippy::msrv = "1.80.0"]
+fn issue14212() {
+    let _ = std::iter::repeat_n((), 5);
+    //~^ ERROR: is `1.80.0` but this item is stable since `1.82.0`
+}
+
 fn main() {}

tests/ui/incompatible_msrv.stderr

@@ -1,5 +1,5 @@
 error: current MSRV (Minimum Supported Rust Version) is `1.3.0` but this item is stable since `1.10.0`
-  --> tests/ui/incompatible_msrv.rs:13:39
+  --> tests/ui/incompatible_msrv.rs:14:39
    |
 LL |     assert_eq!(map.entry("poneyland").key(), &"poneyland");
    |                                       ^^^^^
@@ -8,16 +8,45 @@ LL |     assert_eq!(map.entry("poneyland").key(), &"poneyland");
    = help: to override `-D warnings` add `#[allow(clippy::incompatible_msrv)]`
 
 error: current MSRV (Minimum Supported Rust Version) is `1.3.0` but this item is stable since `1.12.0`
-  --> tests/ui/incompatible_msrv.rs:16:11
+  --> tests/ui/incompatible_msrv.rs:17:11
    |
 LL |         v.into_key();
    |           ^^^^^^^^^^
 
 error: current MSRV (Minimum Supported Rust Version) is `1.3.0` but this item is stable since `1.4.0`
-  --> tests/ui/incompatible_msrv.rs:20:5
+  --> tests/ui/incompatible_msrv.rs:21:5
    |
 LL |     sleep(Duration::new(1, 0));
    |     ^^^^^
 
-error: aborting due to 3 previous errors
+error: current MSRV (Minimum Supported Rust Version) is `1.3.0` but this item is stable since `1.6.0`
+  --> tests/ui/incompatible_msrv.rs:45:9
+   |
+LL |         core::panicking::panic("foo");
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+
+error: current MSRV (Minimum Supported Rust Version) is `1.3.0` but this item is stable since `1.6.0`
+  --> tests/ui/incompatible_msrv.rs:52:13
+   |
+LL |             core::panicking::panic($msg)
+   |             ^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     my_panic!("foo");
+   |     ---------------- in this macro invocation
+   |
+   = note: this error originates in the macro `my_panic` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: current MSRV (Minimum Supported Rust Version) is `1.3.0` but this item is stable since `1.6.0`
+  --> tests/ui/incompatible_msrv.rs:58:13
+   |
+LL |     assert!(core::panicking::panic("out of luck"));
+   |             ^^^^^^^^^^^^^^^^^^^^^^
+
+error: current MSRV (Minimum Supported Rust Version) is `1.80.0` but this item is stable since `1.82.0`
+  --> tests/ui/incompatible_msrv.rs:71:13
+   |
+LL |     let _ = std::iter::repeat_n((), 5);
+   |             ^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 7 previous errors