diff --git a/src/tint/diagnostic/diagnostic.cc b/src/tint/diagnostic/diagnostic.cc
index f7b36a4dec..bd3f297cf6 100644
--- a/src/tint/diagnostic/diagnostic.cc
+++ b/src/tint/diagnostic/diagnostic.cc
@@ -18,8 +18,7 @@
 
 #include "src/tint/diagnostic/formatter.h"
 
-namespace tint {
-namespace diag {
+namespace tint::diag {
 
 Diagnostic::Diagnostic() = default;
 Diagnostic::Diagnostic(const Diagnostic&) = default;
@@ -44,5 +43,4 @@ std::string List::str() const {
   return Formatter{style}.format(*this);
 }
 
-}  // namespace diag
-}  // namespace tint
+}  // namespace tint::diag
diff --git a/src/tint/diagnostic/diagnostic.h b/src/tint/diagnostic/diagnostic.h
index 28b0c6686a..95df55366a 100644
--- a/src/tint/diagnostic/diagnostic.h
+++ b/src/tint/diagnostic/diagnostic.h
@@ -22,8 +22,7 @@
 
 #include "src/tint/source.h"
 
-namespace tint {
-namespace diag {
+namespace tint::diag {
 
 /// Severity is an enumerator of diagnostic severities.
 enum class Severity { Note, Warning, Error, InternalCompilerError, Fatal };
@@ -246,7 +245,6 @@ class List {
   size_t error_count_ = 0;
 };
 
-}  // namespace diag
-}  // namespace tint
+}  // namespace tint::diag
 
 #endif  // SRC_TINT_DIAGNOSTIC_DIAGNOSTIC_H_
diff --git a/src/tint/diagnostic/diagnostic_test.cc b/src/tint/diagnostic/diagnostic_test.cc
index 940971bb56..8bf65e61fa 100644
--- a/src/tint/diagnostic/diagnostic_test.cc
+++ b/src/tint/diagnostic/diagnostic_test.cc
@@ -17,8 +17,7 @@
 #include "gtest/gtest.h"
 #include "src/tint/diagnostic/diagnostic.h"
 
-namespace tint {
-namespace diag {
+namespace tint::diag {
 namespace {
 
 TEST(DiagListTest, OwnedFilesShared) {
@@ -38,5 +37,4 @@ TEST(DiagListTest, OwnedFilesShared) {
 }
 
 }  // namespace
-}  // namespace diag
-}  // namespace tint
+}  // namespace tint::diag
diff --git a/src/tint/diagnostic/formatter.cc b/src/tint/diagnostic/formatter.cc
index 1eabe91889..262be862c5 100644
--- a/src/tint/diagnostic/formatter.cc
+++ b/src/tint/diagnostic/formatter.cc
@@ -21,8 +21,7 @@
 #include "src/tint/diagnostic/diagnostic.h"
 #include "src/tint/diagnostic/printer.h"
 
-namespace tint {
-namespace diag {
+namespace tint::diag {
 namespace {
 
 const char* to_str(Severity severity) {
@@ -267,5 +266,4 @@ std::string Formatter::format(const List& list) const {
 
 Formatter::~Formatter() = default;
 
-}  // namespace diag
-}  // namespace tint
+}  // namespace tint::diag
diff --git a/src/tint/diagnostic/formatter.h b/src/tint/diagnostic/formatter.h
index 209bacb472..179bb2dd95 100644
--- a/src/tint/diagnostic/formatter.h
+++ b/src/tint/diagnostic/formatter.h
@@ -17,8 +17,7 @@
 
 #include <string>
 
-namespace tint {
-namespace diag {
+namespace tint::diag {
 
 class Diagnostic;
 class List;
@@ -66,7 +65,6 @@ class Formatter {
   const Style style_;
 };
 
-}  // namespace diag
-}  // namespace tint
+}  // namespace tint::diag
 
 #endif  // SRC_TINT_DIAGNOSTIC_FORMATTER_H_
diff --git a/src/tint/diagnostic/formatter_test.cc b/src/tint/diagnostic/formatter_test.cc
index cee4140cd0..fc342fb6cc 100644
--- a/src/tint/diagnostic/formatter_test.cc
+++ b/src/tint/diagnostic/formatter_test.cc
@@ -19,8 +19,7 @@
 #include "gtest/gtest.h"
 #include "src/tint/diagnostic/diagnostic.h"
 
-namespace tint {
-namespace diag {
+namespace tint::diag {
 namespace {
 
 Diagnostic Diag(Severity severity,
@@ -306,5 +305,4 @@ TEST_F(DiagFormatterTest, RangeOOB) {
 }
 
 }  // namespace
-}  // namespace diag
-}  // namespace tint
+}  // namespace tint::diag
diff --git a/src/tint/diagnostic/printer.cc b/src/tint/diagnostic/printer.cc
index 54fd5f78ad..a3e93bcffd 100644
--- a/src/tint/diagnostic/printer.cc
+++ b/src/tint/diagnostic/printer.cc
@@ -14,8 +14,7 @@
 
 #include "src/tint/diagnostic/printer.h"
 
-namespace tint {
-namespace diag {
+namespace tint::diag {
 
 Printer::~Printer() = default;
 
@@ -30,5 +29,4 @@ void StringPrinter::write(const std::string& str, const Style&) {
   stream << str;
 }
 
-}  // namespace diag
-}  // namespace tint
+}  // namespace tint::diag
diff --git a/src/tint/diagnostic/printer.h b/src/tint/diagnostic/printer.h
index 570223b17d..cb38ac89e1 100644
--- a/src/tint/diagnostic/printer.h
+++ b/src/tint/diagnostic/printer.h
@@ -19,8 +19,7 @@
 #include <sstream>
 #include <string>
 
-namespace tint {
-namespace diag {
+namespace tint::diag {
 
 class List;
 
@@ -77,7 +76,6 @@ class StringPrinter : public Printer {
   std::stringstream stream;
 };
 
-}  // namespace diag
-}  // namespace tint
+}  // namespace tint::diag
 
 #endif  // SRC_TINT_DIAGNOSTIC_PRINTER_H_
diff --git a/src/tint/diagnostic/printer_linux.cc b/src/tint/diagnostic/printer_linux.cc
index fc40cf3500..9d0e315649 100644
--- a/src/tint/diagnostic/printer_linux.cc
+++ b/src/tint/diagnostic/printer_linux.cc
@@ -18,8 +18,7 @@
 
 #include "src/tint/diagnostic/printer.h"
 
-namespace tint {
-namespace diag {
+namespace tint::diag {
 namespace {
 
 bool supports_colors(FILE* f) {
@@ -96,5 +95,4 @@ std::unique_ptr<Printer> Printer::create(FILE* out, bool use_colors) {
   return std::make_unique<PrinterLinux>(out, use_colors);
 }
 
-}  // namespace diag
-}  // namespace tint
+}  // namespace tint::diag
diff --git a/src/tint/diagnostic/printer_other.cc b/src/tint/diagnostic/printer_other.cc
index 21498beb78..65ef0ac94d 100644
--- a/src/tint/diagnostic/printer_other.cc
+++ b/src/tint/diagnostic/printer_other.cc
@@ -16,8 +16,7 @@
 
 #include "src/tint/diagnostic/printer.h"
 
-namespace tint {
-namespace diag {
+namespace tint::diag {
 namespace {
 
 class PrinterOther : public Printer {
@@ -38,5 +37,4 @@ std::unique_ptr<Printer> Printer::create(FILE* out, bool) {
   return std::make_unique<PrinterOther>(out);
 }
 
-}  // namespace diag
-}  // namespace tint
+}  // namespace tint::diag
diff --git a/src/tint/diagnostic/printer_test.cc b/src/tint/diagnostic/printer_test.cc
index f0cf374624..bfc9d4339a 100644
--- a/src/tint/diagnostic/printer_test.cc
+++ b/src/tint/diagnostic/printer_test.cc
@@ -16,8 +16,7 @@
 
 #include "gtest/gtest.h"
 
-namespace tint {
-namespace diag {
+namespace tint::diag {
 namespace {
 
 // Actually verifying that the expected colors are printed is exceptionally
@@ -94,5 +93,4 @@ TEST_F(PrinterTest, BoldWithoutColors) {
 
 #endif  // ENABLE_PRINTER_TESTS
 }  // namespace
-}  // namespace diag
-}  // namespace tint
+}  // namespace tint::diag
diff --git a/src/tint/diagnostic/printer_windows.cc b/src/tint/diagnostic/printer_windows.cc
index 9dcb43c5a6..e8ebc1923b 100644
--- a/src/tint/diagnostic/printer_windows.cc
+++ b/src/tint/diagnostic/printer_windows.cc
@@ -19,8 +19,7 @@
 #define WIN32_LEAN_AND_MEAN 1
 #include <Windows.h>
 
-namespace tint {
-namespace diag {
+namespace tint::diag {
 namespace {
 
 struct ConsoleInfo {
@@ -109,5 +108,4 @@ std::unique_ptr<Printer> Printer::create(FILE* out, bool use_colors) {
   return std::make_unique<PrinterWindows>(out, use_colors);
 }
 
-}  // namespace diag
-}  // namespace tint
+}  // namespace tint::diag