Handle macros with avoidable_slice_indexing lint

Author: xFrednet

clippy_lints/src/avoidable_slice_indexing.rs

@@ -2,7 +2,7 @@ use clippy_utils::consts::{constant, Constant};
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::higher::IfLet;
 use clippy_utils::ty::implements_trait;
-use clippy_utils::{is_lint_allowed, meets_msrv, msrvs};
+use clippy_utils::{in_macro, is_expn_of, is_lint_allowed, meets_msrv, msrvs};
 use if_chain::if_chain;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::Applicability;
@@ -69,6 +69,7 @@ impl_lint_pass!(AvoidableSliceIndexing =>  [AVOIDABLE_SLICE_INDEXING]);
 impl LateLintPass<'_> for AvoidableSliceIndexing {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
         if_chain! {
+            if !in_macro(expr.span) || is_expn_of(expr.span, "if_chain").is_some();
             if let Some(IfLet {let_pat, if_then, ..}) = IfLet::hir(cx, expr);
             if !is_lint_allowed(cx, AVOIDABLE_SLICE_INDEXING, expr.hir_id);
             if meets_msrv(self.msrv.as_ref(), &msrvs::SLICE_PATTERNS);

tests/ui/avoidable_slice_indexing/slice_indexing_in_macro.rs

@@ -0,0 +1,28 @@
+#![deny(clippy::avoidable_slice_indexing)]
+
+extern crate if_chain;
+use if_chain::if_chain;
+
+macro_rules! if_let_slice_macro {
+    () => {
+        // This would normally be linted
+        let slice: Option<&[u32]> = Some(&[1, 2, 3]);
+        if let Some(slice) = slice {
+            println!("{}", slice[0]);
+        }
+    };
+}
+
+fn main() {
+    // Don't lint this
+    if_let_slice_macro!();
+
+    // Do lint this
+    if_chain! {
+        let slice: Option<&[u32]> = Some(&[1, 2, 3]);
+        if let Some(slice) = slice;
+        then {
+            println!("{}", slice[0]);
+        }
+    }
+}

tests/ui/avoidable_slice_indexing/slice_indexing_in_macro.stderr

@@ -0,0 +1,22 @@
+error: this slice can be deconstructured to avoid indexing
+  --> $DIR/slice_indexing_in_macro.rs:24:21
+   |
+LL |         if let Some(slice) = slice;
+   |                     ^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/slice_indexing_in_macro.rs:1:9
+   |
+LL | #![deny(clippy::avoidable_slice_indexing)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: try destructing the slice with a pattern here
+   |
+LL |         if let Some([slice_0, ..]) = slice;
+   |                     ~~~~~~~~~~~~~
+help: and replacing the index expressions here
+   |
+LL |             println!("{}", slice_0);
+   |                            ~~~~~~~
+
+error: aborting due to previous error
+