3 files changed, 18 insertions, 19 deletions

diff --git a/crates/ra_hir_ty/src/diagnostics.rs b/crates/ra_hir_ty/src/diagnostics.rs
index 6eafdc8f6..0f8522021 100644
--- a/crates/ra_hir_ty/src/diagnostics.rs
+++ b/crates/ra_hir_ty/src/diagnostics.rs
@@ -4,6 +4,7 @@ use std::any::Any;
 
 use hir_expand::{db::AstDatabase, name::Name, HirFileId, InFile};
 use ra_syntax::{ast, AstNode, AstPtr, SyntaxNodePtr};
+use stdx::format_to;
 
 pub use hir_def::diagnostics::UnresolvedModule;
 pub use hir_expand::diagnostics::{AstDiagnostic, Diagnostic, DiagnosticSink};
@@ -37,12 +38,11 @@ pub struct MissingFields {
 
 impl Diagnostic for MissingFields {
     fn message(&self) -> String {
-        use std::fmt::Write;
-        let mut message = String::from("Missing structure fields:\n");
+        let mut buf = String::from("Missing structure fields:\n");
         for field in &self.missed_fields {
-            writeln!(message, "- {}", field).unwrap();
+            format_to!(buf, "- {}", field);
         }
-        message
+        buf
     }
     fn source(&self) -> InFile<SyntaxNodePtr> {
         InFile { file_id: self.file, value: self.field_list.into() }
diff --git a/crates/ra_hir_ty/src/test_db.rs b/crates/ra_hir_ty/src/test_db.rs
index 5bbeabf51..208096aab 100644
--- a/crates/ra_hir_ty/src/test_db.rs
+++ b/crates/ra_hir_ty/src/test_db.rs
@@ -10,6 +10,7 @@ use hir_expand::{db::AstDatabase, diagnostics::DiagnosticSink};
 use ra_db::{
     salsa, CrateId, FileId, FileLoader, FileLoaderDelegate, RelativePath, SourceDatabase, Upcast,
 };
+use stdx::format_to;
 
 use crate::{db::HirDatabase, expr::ExprValidator};
 
@@ -131,7 +132,7 @@ impl TestDB {
             for f in fns {
                 let infer = self.infer(f.into());
                 let mut sink = DiagnosticSink::new(|d| {
-                    buf += &format!("{:?}: {}\n", d.syntax_node(self).text(), d.message());
+                    format_to!(buf, "{:?}: {}\n", d.syntax_node(self).text(), d.message());
                 });
                 infer.add_diagnostics(self, f, &mut sink);
                 let mut validator = ExprValidator::new(f, infer, &mut sink);
diff --git a/crates/ra_hir_ty/src/tests.rs b/crates/ra_hir_ty/src/tests.rs
index 7e9547340..027e5a8f8 100644
--- a/crates/ra_hir_ty/src/tests.rs
+++ b/crates/ra_hir_ty/src/tests.rs
@@ -7,7 +7,6 @@ mod traits;
 mod method_resolution;
 mod macros;
 
-use std::fmt::Write;
 use std::sync::Arc;
 
 use hir_def::{
@@ -26,6 +25,7 @@ use ra_syntax::{
     algo,
     ast::{self, AstNode},
 };
+use stdx::format_to;
 
 use crate::{db::HirDatabase, display::HirDisplay, test_db::TestDB, InferenceResult};
 
@@ -63,7 +63,7 @@ fn infer(ra_fixture: &str) -> String {
 fn infer_with_mismatches(content: &str, include_mismatches: bool) -> String {
     let (db, file_id) = TestDB::with_single_file(content);
 
-    let mut acc = String::new();
+    let mut buf = String::new();
 
     let mut infer_def = |inference_result: Arc<InferenceResult>,
                          body_source_map: Arc<BodySourceMap>| {
@@ -106,15 +106,14 @@ fn infer_with_mismatches(content: &str, include_mismatches: bool) -> String {
                 (src_ptr.value.range(), node.text().to_string().replace("\n", " "))
             };
             let macro_prefix = if src_ptr.file_id != file_id.into() { "!" } else { "" };
-            writeln!(
-                acc,
-                "{}{} '{}': {}",
+            format_to!(
+                buf,
+                "{}{} '{}': {}\n",
                 macro_prefix,
                 range,
                 ellipsize(text, 15),
                 ty.display(&db)
-            )
-            .unwrap();
+            );
         }
         if include_mismatches {
             mismatches.sort_by_key(|(src_ptr, _)| {
@@ -123,15 +122,14 @@ fn infer_with_mismatches(content: &str, include_mismatches: bool) -> String {
             for (src_ptr, mismatch) in &mismatches {
                 let range = src_ptr.value.range();
                 let macro_prefix = if src_ptr.file_id != file_id.into() { "!" } else { "" };
-                writeln!(
-                    acc,
-                    "{}{}: expected {}, got {}",
+                format_to!(
+                    buf,
+                    "{}{}: expected {}, got {}\n",
                     macro_prefix,
                     range,
                     mismatch.expected.display(&db),
                     mismatch.actual.display(&db),
-                )
-                .unwrap();
+                );
             }
         }
     };
@@ -158,8 +156,8 @@ fn infer_with_mismatches(content: &str, include_mismatches: bool) -> String {
         infer_def(infer, source_map);
     }
 
-    acc.truncate(acc.trim_end().len());
-    acc
+    buf.truncate(buf.trim_end().len());
+    buf
 }
 
 fn visit_module(