From cb66bb8ff9609d4fc3702ac1ed6197802b54e473 Mon Sep 17 00:00:00 2001
From: ivan770 <leshenko.ivan770@gmail.com>
Date: Tue, 8 Dec 2020 20:47:20 +0200
Subject: Remove this semicolon

---
 crates/hir_ty/src/diagnostics.rs      | 24 ++++++++++++++++++++++++
 crates/hir_ty/src/diagnostics/expr.rs | 27 ++++++++++++++++++++++++++-
 2 files changed, 50 insertions(+), 1 deletion(-)

(limited to 'crates/hir_ty')

diff --git a/crates/hir_ty/src/diagnostics.rs b/crates/hir_ty/src/diagnostics.rs
index b58fe0ed7..e59487e54 100644
--- a/crates/hir_ty/src/diagnostics.rs
+++ b/crates/hir_ty/src/diagnostics.rs
@@ -216,6 +216,30 @@ impl Diagnostic for MissingOkInTailExpr {
     }
 }
 
+#[derive(Debug)]
+pub struct RemoveThisSemicolon {
+    pub file: HirFileId,
+    pub expr: AstPtr<ast::Expr>,
+}
+
+impl Diagnostic for RemoveThisSemicolon {
+    fn code(&self) -> DiagnosticCode {
+        DiagnosticCode("remove-this-semicolon")
+    }
+
+    fn message(&self) -> String {
+        "Remove this semicolon".to_string()
+    }
+
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile { file_id: self.file, value: self.expr.clone().into() }
+    }
+
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}
+
 // Diagnostic: break-outside-of-loop
 //
 // This diagnostic is triggered if `break` keyword is used outside of a loop.
diff --git a/crates/hir_ty/src/diagnostics/expr.rs b/crates/hir_ty/src/diagnostics/expr.rs
index 434b19354..313422968 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::{AdtId, DefWithBodyId, expr::Statement, path::path, resolver::HasResolver};
 use hir_expand::diagnostics::DiagnosticSink;
 use rustc_hash::FxHashSet;
 use syntax::{ast, AstPtr};
@@ -23,6 +23,8 @@ pub(crate) use hir_def::{
     LocalFieldId, VariantId,
 };
 
+use super::RemoveThisSemicolon;
+
 pub(super) struct ExprValidator<'a, 'b: 'a> {
     owner: DefWithBodyId,
     infer: Arc<InferenceResult>,
@@ -78,6 +80,12 @@ 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);
+        } else {
+            if let Expr::Block { statements, .. } = body_expr {
+                if let Some(Statement::Expr(id)) = statements.last() {
+                    self.validate_missing_tail_expr(body.body_expr, *id, db);
+                }
+            }
         }
     }
 
@@ -317,6 +325,23 @@ 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,
+        };
+
+        if let Some(possible_tail_ty) = self.infer.type_of_expr.get(possible_tail_id) {
+            if mismatch.actual == Ty::unit() && mismatch.expected == *possible_tail_ty {
+                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(
-- 
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