Merge #6769

6769: Add native "remove this semicolon" diagnostics r=matklad a=ivan770

Closes #6739 
![demo2](https://user-images.githubusercontent.com/14003886/101530533-b76c3180-399a-11eb-9d18-5c8457721655.gif)


Co-authored-by: ivan770 <[email protected]>

1 files changed, 36 insertions, 3 deletions

diff --git a/crates/hir_ty/src/diagnostics/expr.rs b/crates/hir_ty/src/diagnostics/expr.rs
index 434b19354..849415706 100644
--- a/crates/hir_ty/src/diagnostics/expr.rs
+++ b/crates/hir_ty/src/diagnostics/expr.rs
@@ -2,7 +2,7 @@
 
 use std::sync::Arc;
 
-use hir_def::{path::path, resolver::HasResolver, AdtId, DefWithBodyId};
+use hir_def::{expr::Statement, path::path, resolver::HasResolver, AdtId, DefWithBodyId};
 use hir_expand::diagnostics::DiagnosticSink;
 use rustc_hash::FxHashSet;
 use syntax::{ast, AstPtr};
@@ -12,6 +12,7 @@ use crate::{
     diagnostics::{
         match_check::{is_useful, MatchCheckCtx, Matrix, PatStack, Usefulness},
         MismatchedArgCount, MissingFields, MissingMatchArms, MissingOkInTailExpr, MissingPatFields,
+        RemoveThisSemicolon,
     },
     utils::variant_data,
     ApplicationTy, InferenceResult, Ty, TypeCtor,
@@ -76,8 +77,12 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
             }
         }
         let body_expr = &body[body.body_expr];
-        if let Expr::Block { tail: Some(t), .. } = body_expr {
-            self.validate_results_in_tail_expr(body.body_expr, *t, db);
+        if let Expr::Block { statements, tail, .. } = body_expr {
+            if let Some(t) = tail {
+                self.validate_results_in_tail_expr(body.body_expr, *t, db);
+            } else if let Some(Statement::Expr(id)) = statements.last() {
+                self.validate_missing_tail_expr(body.body_expr, *id, db);
+            }
         }
     }
 
@@ -317,6 +322,34 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
             }
         }
     }
+
+    fn validate_missing_tail_expr(
+        &mut self,
+        body_id: ExprId,
+        possible_tail_id: ExprId,
+        db: &dyn HirDatabase,
+    ) {
+        let mismatch = match self.infer.type_mismatch_for_expr(body_id) {
+            Some(m) => m,
+            None => return,
+        };
+
+        let possible_tail_ty = match self.infer.type_of_expr.get(possible_tail_id) {
+            Some(ty) => ty,
+            None => return,
+        };
+
+        if mismatch.actual != Ty::unit() || mismatch.expected != *possible_tail_ty {
+            return;
+        }
+
+        let (_, source_map) = db.body_with_source_map(self.owner.into());
+
+        if let Ok(source_ptr) = source_map.expr_syntax(possible_tail_id) {
+            self.sink
+                .push(RemoveThisSemicolon { file: source_ptr.file_id, expr: source_ptr.value });
+        }
+    }
 }
 
 pub fn record_literal_missing_fields(