fix tests and code cleanup

Author: chenyukang

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1816,11 +1816,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         if let Some(Expr { kind: ExprKind::Assign(lhs, rhs, _), .. }) =
             self.diagnostic_metadata.in_assignment
         {
-            let is_rhs_assign = match rhs.kind {
-                ExprKind::Assign(..) => true,
-                _ => false,
-            };
-
+            let is_rhs_assign = matches!(rhs.kind, ExprKind::Assign(..));
             if let ast::ExprKind::Path(None, _) = lhs.kind && !is_rhs_assign {
                 let sm = self.r.session.source_map();
                 let line_span = sm.span_extend_to_line(ident_span);

src/test/ui/suggestions/issue-104086-suggest-let.rs

@@ -1,10 +1,30 @@
-// error-pattern: not found in this scope
-
 fn main() {
     x = x = x;
+    //~^ ERROR cannot find value `x` in this scope
+    //~| ERROR cannot find value `x` in this scope
+    //~| ERROR cannot find value `x` in this scope
+
     x = y = y = y;
+    //~^ ERROR cannot find value `y` in this scope
+    //~| ERROR cannot find value `y` in this scope
+    //~| ERROR cannot find value `y` in this scope
+    //~| ERROR cannot find value `x` in this scope
+
     x = y = y;
+    //~^ ERROR cannot find value `x` in this scope
+    //~| ERROR cannot find value `y` in this scope
+    //~| ERROR cannot find value `y` in this scope
+
     x = x = y;
+    //~^ ERROR cannot find value `x` in this scope
+    //~| ERROR cannot find value `x` in this scope
+    //~| ERROR cannot find value `y` in this scope
+
     x = x; // will suggest add `let`
+    //~^ ERROR cannot find value `x` in this scope
+    //~| ERROR cannot find value `x` in this scope
+
     x = y // will suggest add `let`
+    //~^ ERROR cannot find value `x` in this scope
+    //~| ERROR cannot find value `y` in this scope
 }

src/test/ui/suggestions/issue-104086-suggest-let.stderr

@@ -1,81 +1,115 @@
 error[E0425]: cannot find value `x` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:4:5
+  --> $DIR/issue-104086-suggest-let.rs:2:5
    |
 LL |     x = x = x;
    |     ^ not found in this scope
 
 error[E0425]: cannot find value `x` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:4:9
+  --> $DIR/issue-104086-suggest-let.rs:2:9
    |
 LL |     x = x = x;
    |         ^ not found in this scope
 
 error[E0425]: cannot find value `x` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:4:13
+  --> $DIR/issue-104086-suggest-let.rs:2:13
    |
 LL |     x = x = x;
    |             ^ not found in this scope
 
 error[E0425]: cannot find value `x` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:5:5
+  --> $DIR/issue-104086-suggest-let.rs:7:5
    |
 LL |     x = y = y = y;
    |     ^ not found in this scope
 
 error[E0425]: cannot find value `y` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:5:9
+  --> $DIR/issue-104086-suggest-let.rs:7:9
    |
 LL |     x = y = y = y;
    |         ^ not found in this scope
 
 error[E0425]: cannot find value `y` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:5:13
+  --> $DIR/issue-104086-suggest-let.rs:7:13
    |
 LL |     x = y = y = y;
    |             ^ not found in this scope
 
 error[E0425]: cannot find value `y` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:5:17
+  --> $DIR/issue-104086-suggest-let.rs:7:17
    |
 LL |     x = y = y = y;
    |                 ^ not found in this scope
 
 error[E0425]: cannot find value `x` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:6:5
+  --> $DIR/issue-104086-suggest-let.rs:13:5
    |
 LL |     x = y = y;
    |     ^ not found in this scope
 
 error[E0425]: cannot find value `y` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:6:9
+  --> $DIR/issue-104086-suggest-let.rs:13:9
    |
 LL |     x = y = y;
    |         ^ not found in this scope
 
 error[E0425]: cannot find value `y` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:6:13
+  --> $DIR/issue-104086-suggest-let.rs:13:13
    |
 LL |     x = y = y;
    |             ^ not found in this scope
 
 error[E0425]: cannot find value `x` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:7:5
+  --> $DIR/issue-104086-suggest-let.rs:18:5
    |
 LL |     x = x = y;
    |     ^ not found in this scope
 
 error[E0425]: cannot find value `x` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:7:9
+  --> $DIR/issue-104086-suggest-let.rs:18:9
    |
 LL |     x = x = y;
    |         ^ not found in this scope
 
 error[E0425]: cannot find value `y` in this scope
-  --> $DIR/issue-104086-suggest-let.rs:7:13
+  --> $DIR/issue-104086-suggest-let.rs:18:13
    |
 LL |     x = x = y;
    |             ^ not found in this scope
 
-error: aborting due to 13 previous errors
+error[E0425]: cannot find value `x` in this scope
+  --> $DIR/issue-104086-suggest-let.rs:23:5
+   |
+LL |     x = x; // will suggest add `let`
+   |     ^
+   |
+help: you might have meant to introduce a new binding
+   |
+LL |     let x = x; // will suggest add `let`
+   |     +++
+
+error[E0425]: cannot find value `x` in this scope
+  --> $DIR/issue-104086-suggest-let.rs:23:9
+   |
+LL |     x = x; // will suggest add `let`
+   |         ^ not found in this scope
+
+error[E0425]: cannot find value `x` in this scope
+  --> $DIR/issue-104086-suggest-let.rs:27:5
+   |
+LL |     x = y // will suggest add `let`
+   |     ^
+   |
+help: you might have meant to introduce a new binding
+   |
+LL |     let x = y // will suggest add `let`
+   |     +++
+
+error[E0425]: cannot find value `y` in this scope
+  --> $DIR/issue-104086-suggest-let.rs:27:9
+   |
+LL |     x = y // will suggest add `let`
+   |         ^ not found in this scope
+
+error: aborting due to 17 previous errors
 
 For more information about this error, try `rustc --explain E0425`.