Fix single_match suggestions with expanded macros

Author: phansch

clippy_lints/src/matches.rs

@@ -13,12 +13,13 @@ use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass, in_exte
 use crate::rustc::{declare_tool_lint, lint_array};
 use if_chain::if_chain;
 use crate::rustc::ty::{self, Ty};
+use std::borrow::Cow;
 use std::cmp::Ordering;
 use std::collections::Bound;
 use crate::syntax::ast::LitKind;
 use crate::syntax::source_map::Span;
 use crate::utils::paths;
-use crate::utils::{expr_block, is_allowed, is_expn_of, match_qpath, match_type, multispan_sugg,
+use crate::utils::{expr_block, in_macro, is_allowed, is_expn_of, match_qpath, match_type, multispan_sugg,
             remove_blocks, snippet, span_lint_and_sugg, span_lint_and_then, span_note_and_lint, walk_ptrs_ty};
 use crate::utils::sugg::Sugg;
 use crate::consts::{constant, Constant};
@@ -254,7 +255,18 @@ fn report_single_match_single_pattern(cx: &LateContext<'_, '_>, ex: &Expr, arms:
     } else {
         SINGLE_MATCH
     };
-    let els_str = els.map_or(String::new(), |els| format!(" else {}", expr_block(cx, els, None, "..")));
+    let els_str = els.map_or(String::new(), |els| {
+        if in_macro(els.span) {
+            " else {{ .. }}".to_string()
+        } else {
+            format!(" else {}", expr_block(cx, els, None, ".."))
+        }
+    });
+    let expr_block = if in_macro(arms[0].body.span) {
+        Cow::Owned("{ .. }".to_string())
+    } else {
+        expr_block(cx, &arms[0].body, None, "..")
+    };
     span_lint_and_sugg(
         cx,
         lint,
@@ -266,7 +278,7 @@ fn report_single_match_single_pattern(cx: &LateContext<'_, '_>, ex: &Expr, arms:
             "if let {} = {} {}{}",
             snippet(cx, arms[0].pats[0].span, ".."),
             snippet(cx, ex.span, ".."),
-            expr_block(cx, &arms[0].body, None, ".."),
+            expr_block,
             els_str
         ),
     );

tests/ui/matches.stderr

@@ -33,7 +33,7 @@ error: you seem to be trying to use match for destructuring a single pattern. Co
 51 | |         &(v, 1) => println!("{}", v),
 52 | |         _ => println!("none"),
 53 | |     }
-   | |_____^ help: try this: `if let &(v, 1) = tup { $ crate :: io :: _print ( format_args_nl ! ( $ ( $ arg ) * ) ) ; } else { $ crate :: io :: _print ( format_args_nl ! ( $ ( $ arg ) * ) ) ; }`
+   | |_____^ help: try this: `if let &(v, 1) = tup { .. } else { .. }`
 
 error: you don't need to add `&` to all patterns
   --> $DIR/matches.rs:50:5

tests/ui/single_match.rs

@@ -23,6 +23,15 @@ fn single_match(){
         _ => ()
     };
 
+    let x = Some(1u8);
+    match x {
+        // Note the missing block braces.
+        // We suggest `if let Some(y) = x { .. }` because the macro
+        // is expanded before we can do anything.
+        Some(y) => println!("{:?}", y),
+        _ => ()
+    }
+
     let z = (1u8,1u8);
     match z {
         (2...3, 7...9) => dummy(),

tests/ui/single_match.stderr

@@ -12,38 +12,50 @@ error: you seem to be trying to use match for destructuring a single pattern. Co
 error: you seem to be trying to use match for destructuring a single pattern. Consider using `if let`
   --> $DIR/single_match.rs:27:5
    |
-27 | /     match z {
-28 | |         (2...3, 7...9) => dummy(),
-29 | |         _ => {}
-30 | |     };
+27 | /     match x {
+28 | |         // Note the missing block braces.
+29 | |         // We suggest `if let Some(y) = x { .. }` because the macro
+30 | |         // is expanded before we can do anything.
+31 | |         Some(y) => println!("{:?}", y),
+32 | |         _ => ()
+33 | |     }
+   | |_____^ help: try this: `if let Some(y) = x { .. }`
+
+error: you seem to be trying to use match for destructuring a single pattern. Consider using `if let`
+  --> $DIR/single_match.rs:36:5
+   |
+36 | /     match z {
+37 | |         (2...3, 7...9) => dummy(),
+38 | |         _ => {}
+39 | |     };
    | |_____^ help: try this: `if let (2...3, 7...9) = z { dummy() }`
 
 error: you seem to be trying to use match for destructuring a single pattern. Consider using `if let`
-  --> $DIR/single_match.rs:53:5
+  --> $DIR/single_match.rs:62:5
    |
-53 | /     match x {
-54 | |         Some(y) => dummy(),
-55 | |         None => ()
-56 | |     };
+62 | /     match x {
+63 | |         Some(y) => dummy(),
+64 | |         None => ()
+65 | |     };
    | |_____^ help: try this: `if let Some(y) = x { dummy() }`
 
 error: you seem to be trying to use match for destructuring a single pattern. Consider using `if let`
-  --> $DIR/single_match.rs:58:5
+  --> $DIR/single_match.rs:67:5
    |
-58 | /     match y {
-59 | |         Ok(y) => dummy(),
-60 | |         Err(..) => ()
-61 | |     };
+67 | /     match y {
+68 | |         Ok(y) => dummy(),
+69 | |         Err(..) => ()
+70 | |     };
    | |_____^ help: try this: `if let Ok(y) = y { dummy() }`
 
 error: you seem to be trying to use match for destructuring a single pattern. Consider using `if let`
-  --> $DIR/single_match.rs:65:5
+  --> $DIR/single_match.rs:74:5
    |
-65 | /     match c {
-66 | |         Cow::Borrowed(..) => dummy(),
-67 | |         Cow::Owned(..) => (),
-68 | |     };
+74 | /     match c {
+75 | |         Cow::Borrowed(..) => dummy(),
+76 | |         Cow::Owned(..) => (),
+77 | |     };
    | |_____^ help: try this: `if let Cow::Borrowed(..) = c { dummy() }`
 
-error: aborting due to 5 previous errors
+error: aborting due to 6 previous errors