Give better suggestion by working on span on deref_addrof lint

Author: ThibsG

clippy_lints/src/reference.rs

@@ -1,9 +1,11 @@
-use crate::utils::{in_macro, snippet_with_applicability, span_lint_and_sugg};
+use crate::utils::{in_macro, snippet_opt, snippet_with_applicability, span_lint_and_sugg};
 use if_chain::if_chain;
-use rustc_ast::ast::{Expr, ExprKind, UnOp};
+use rustc_ast::ast::{Expr, ExprKind, UnOp, Mutability};
 use rustc_errors::Applicability;
 use rustc_lint::{EarlyContext, EarlyLintPass};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::BytePos;
+// use rustc_span::source_map::{BytePos, Span};
 
 declare_clippy_lint! {
     /// **What it does:** Checks for usage of `*&` and `*&mut` in expressions.
@@ -42,13 +44,37 @@ impl EarlyLintPass for DerefAddrOf {
     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &Expr) {
         if_chain! {
             if let ExprKind::Unary(UnOp::Deref, ref deref_target) = e.kind;
-            if let ExprKind::AddrOf(_, _, ref addrof_target) = without_parens(deref_target).kind;
+            if let ExprKind::AddrOf(_, ref mutability, ref addrof_target) = without_parens(deref_target).kind;
             if !in_macro(addrof_target.span);
             then {
                 let mut applicability = Applicability::MachineApplicable;
                 let sugg = if e.span.from_expansion() {
-                    let snip = snippet_with_applicability(cx, e.span, "_", &mut applicability);
-                    snip.trim_start_matches(|c| c == '&' || c == '*').to_string()
+                    if let Ok(macro_source) = cx.sess.source_map().span_to_snippet(e.span) {
+                        // Remove leading whitespace from the given span
+                        // e.g: ` $visitor` turns into `$visitor`
+                        let trim_leading_whitespaces = |span| {
+                            if let Some(start_no_whitespace) = snippet_opt(cx, span).and_then(|snip| {
+                                snip.find(|c: char| !c.is_whitespace()).map(|pos| {
+                                    span.lo() + BytePos(pos as u32)
+                                })
+                            }) {
+                                e.span.with_lo(start_no_whitespace)
+                            } else {
+                                span
+                            }
+                        };
+
+                        let rpos = if *mutability == Mutability::Mut {
+                            macro_source.rfind("mut").expect("already checked this is a mutable reference") + "mut".len()
+                        } else {
+                            macro_source.rfind("&").expect("already checked this is a reference") + "&".len()
+                        };
+                        let span_after_ref = e.span.with_lo(BytePos(e.span.lo().0 + rpos as u32));
+                        let span = trim_leading_whitespaces(span_after_ref);
+                        snippet_with_applicability(cx, span, "_", &mut applicability).to_string()
+                    } else {
+                        snippet_with_applicability(cx, e.span, "_", &mut applicability).to_string()
+                    }
                 } else {
                     snippet_with_applicability(cx, addrof_target.span, "_", &mut applicability).to_string()
                 };

tests/ui/deref_addrof.fixed

@@ -44,9 +44,19 @@ macro_rules! m {
     };
 }
 
+#[rustfmt::skip]
+macro_rules! m_mut {
+    ($visitor: expr) => {
+        $visitor
+    };
+}
+
 pub struct S;
 impl S {
     pub fn f(&self) -> &Self {
         m!(self)
     }
+    pub fn f_mut(&self) -> &Self {
+        m_mut!(self)
+    }
 }

tests/ui/deref_addrof.rs

@@ -40,7 +40,14 @@ fn main() {
 
 macro_rules! m {
     ($visitor: expr) => {
-        *&$visitor
+        *& $visitor
+    };
+}
+
+#[rustfmt::skip]
+macro_rules! m_mut {
+    ($visitor: expr) => {
+        *& mut $visitor
     };
 }
 
@@ -49,4 +56,7 @@ impl S {
     pub fn f(&self) -> &Self {
         m!(self)
     }
+    pub fn f_mut(&self) -> &Self {
+        m_mut!(self)
+    }
 }

tests/ui/deref_addrof.stderr

@@ -51,13 +51,24 @@ LL |     let b = **&aref;
 error: immediately dereferencing a reference
   --> $DIR/deref_addrof.rs:43:9
    |
-LL |         *&$visitor
-   |         ^^^^^^^^^^ help: try this: `$visitor`
+LL |         *& $visitor
+   |         ^^^^^^^^^^^ help: try this: `$visitor`
 ...
 LL |         m!(self)
    |         -------- in this macro invocation
    |
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 9 previous errors
+error: immediately dereferencing a reference
+  --> $DIR/deref_addrof.rs:50:9
+   |
+LL |         *& mut $visitor
+   |         ^^^^^^^^^^^^^^^ help: try this: `$visitor`
+...
+LL |         m_mut!(self)
+   |         ------------ in this macro invocation
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 10 previous errors