Fix find_format_arg_expr when incremental compilation is enabled

Author: Alexendoo

clippy_utils/src/macros.rs

@@ -9,7 +9,7 @@ use rustc_hir::{self as hir, Expr, ExprKind, HirId, Node, QPath};
 use rustc_lint::LateContext;
 use rustc_span::def_id::DefId;
 use rustc_span::hygiene::{self, MacroKind, SyntaxContext};
-use rustc_span::{sym, BytePos, ExpnData, ExpnId, ExpnKind, Span, Symbol};
+use rustc_span::{sym, BytePos, ExpnData, ExpnId, ExpnKind, Span, SpanData, Symbol};
 use std::cell::RefCell;
 use std::ops::ControlFlow;
 use std::sync::atomic::{AtomicBool, Ordering};
@@ -415,8 +415,18 @@ pub fn find_format_arg_expr<'hir, 'ast>(
     start: &'hir Expr<'hir>,
     target: &'ast FormatArgument,
 ) -> Result<&'hir rustc_hir::Expr<'hir>, &'ast rustc_ast::Expr> {
+    let SpanData {
+        lo,
+        hi,
+        ctxt,
+        parent: _,
+    } = target.expr.span.data();
+
     for_each_expr(start, |expr| {
-        if expr.span == target.expr.span {
+        // When incremental compilation is enabled spans gain a parent during AST to HIR lowering,
+        // since we're comparing an AST span to a HIR one we need to ignore the parent field
+        let data = expr.span.data();
+        if data.lo == lo && data.hi == hi && data.ctxt == ctxt {
             ControlFlow::Break(expr)
         } else {
             ControlFlow::Continue(())

tests/ui/to_string_in_format_args_incremental.fixed

@@ -0,0 +1,9 @@
+//@run-rustfix
+//@compile-flags: -C incremental=target/debug/test/incr
+
+// see https://github.com/rust-lang/rust-clippy/issues/10969
+
+fn main() {
+    let s = "Hello, world!";
+    println!("{}", s);
+}

tests/ui/to_string_in_format_args_incremental.rs

@@ -0,0 +1,9 @@
+//@run-rustfix
+//@compile-flags: -C incremental=target/debug/test/incr
+
+// see https://github.com/rust-lang/rust-clippy/issues/10969
+
+fn main() {
+    let s = "Hello, world!";
+    println!("{}", s.to_string());
+}

tests/ui/to_string_in_format_args_incremental.stderr

@@ -0,0 +1,10 @@
+error: `to_string` applied to a type that implements `Display` in `println!` args
+  --> $DIR/to_string_in_format_args_incremental.rs:8:21
+   |
+LL |     println!("{}", s.to_string());
+   |                     ^^^^^^^^^^^^ help: remove this
+   |
+   = note: `-D clippy::to-string-in-format-args` implied by `-D warnings`
+
+error: aborting due to previous error
+