diff --git a/mlir/include/mlir/IR/Diagnostics.h b/mlir/include/mlir/IR/Diagnostics.h
--- a/mlir/include/mlir/IR/Diagnostics.h
+++ b/mlir/include/mlir/IR/Diagnostics.h
@@ -523,6 +523,43 @@
   MLIRContext *ctx;
 };
 
+//===----------------------------------------------------------------------===//
+// ScopedDiagInspectorHandler
+//===----------------------------------------------------------------------===//
+
+/// This is a RAII class for inspecting the diagnostic. It can be used to
+/// collect the information at a certain program scope. It's mainly for
+/// debugging purpose.
+class ScopedDiagInspectorHandler {
+public:
+  /// An inspector is only supposed to read the diagnostic so it shouldn't
+  /// update it.
+  using InspectorTy = std::function<LogicalResult(const Diagnostic &)>;
+
+  ScopedDiagInspectorHandler(MLIRContext *ctx, InspectorTy inspector)
+      : ctx(ctx), inspector(inspector) {
+    auto &diagEngine = ctx->getDiagEngine();
+    handlerID =
+        diagEngine.registerHandler([this](Diagnostic &diag) -> LogicalResult {
+          (void)this->inspector(diag);
+          // Inspector is supposed to only read the diagnostic, return failure
+          // to let other handlers do their job.
+          return failure();
+        });
+  }
+  ~ScopedDiagInspectorHandler();
+
+private:
+  /// The context to erase the handler from.
+  MLIRContext *ctx;
+
+  /// The inspector registered by the user.
+  InspectorTy inspector;
+
+  /// The handler id returned by the DiagEngine.
+  DiagnosticEngine::HandlerID handlerID;
+};
+
 //===----------------------------------------------------------------------===//
 // SourceMgrDiagnosticHandler
 //===----------------------------------------------------------------------===//
diff --git a/mlir/lib/IR/Diagnostics.cpp b/mlir/lib/IR/Diagnostics.cpp
--- a/mlir/lib/IR/Diagnostics.cpp
+++ b/mlir/lib/IR/Diagnostics.cpp
@@ -337,6 +337,13 @@
     ctx->getDiagEngine().eraseHandler(handlerID);
 }
 
+//===----------------------------------------------------------------------===//
+// ScopedDiagInspectorHandler
+//===----------------------------------------------------------------------===//
+ScopedDiagInspectorHandler::~ScopedDiagInspectorHandler() {
+  ctx->getDiagEngine().eraseHandler(handlerID);
+}
+
 //===----------------------------------------------------------------------===//
 // SourceMgrDiagnosticHandler
 //===----------------------------------------------------------------------===//
diff --git a/mlir/lib/Transforms/Utils/DialectConversion.cpp b/mlir/lib/Transforms/Utils/DialectConversion.cpp
--- a/mlir/lib/Transforms/Utils/DialectConversion.cpp
+++ b/mlir/lib/Transforms/Utils/DialectConversion.cpp
@@ -1298,6 +1298,8 @@
     Diagnostic diag(loc, DiagnosticSeverity::Remark);
     reasonCallback(diag);
     logger.startLine() << "** Failure : " << diag.str() << "\n";
+    // Emit to the DiagEngine so that the inspector can get notified.
+    loc->getContext()->getDiagEngine().emit(std::move(diag));
   });
   return failure();
 }
diff --git a/mlir/test/IR/diagnostic-inspector.mlir b/mlir/test/IR/diagnostic-inspector.mlir
new file mode 100644
--- /dev/null
+++ b/mlir/test/IR/diagnostic-inspector.mlir
@@ -0,0 +1,8 @@
+// RUN: mlir-opt -test-diagnostic-inspector %s
+// This test verifies that diagnostic inspector can capture the diagnostics.
+
+func @test_diagnostic_inspector() {
+  "test.dummy_0"() : () -> ()
+  "test.dummy_1"() : () -> ()
+  return
+}
diff --git a/mlir/test/lib/IR/TestDiagnostics.cpp b/mlir/test/lib/IR/TestDiagnostics.cpp
--- a/mlir/test/lib/IR/TestDiagnostics.cpp
+++ b/mlir/test/lib/IR/TestDiagnostics.cpp
@@ -11,12 +11,48 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "mlir/IR/Diagnostics.h"
 #include "mlir/Pass/Pass.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/SourceMgr.h"
 
+#include <string>
+
 using namespace mlir;
 
 namespace {
+struct TestDiagnosticInspectorPass
+    : public PassWrapper<TestDiagnosticInspectorPass, OperationPass<FuncOp>> {
+  StringRef getArgument() const final { return "test-diagnostic-inspector"; }
+  StringRef getDescription() const final {
+    return "Test diagnostic inspector support.";
+  }
+
+  TestDiagnosticInspectorPass() {}
+  TestDiagnosticInspectorPass(const TestDiagnosticInspectorPass &) {}
+
+  void runOnOperation() override {
+    llvm::SmallVector<std::string> opNames;
+    ScopedDiagInspectorHandler inspector(
+        &getContext(), [&](const Diagnostic &diag) -> LogicalResult {
+          opNames.push_back(diag.str());
+          return success();
+        });
+
+    getOperation()->walk([&](Operation *op) {
+      // Emit the operation name for inspector.
+      op->emitRemark() << op->getName().getStringRef();
+    });
+
+    // Verify the operation names are captured by the inspector.
+    auto nameIter = opNames.begin();
+    getOperation()->walk([&](Operation *op) {
+      assert(op->getName().getStringRef().equals(*nameIter));
+      ++nameIter;
+    });
+  }
+};
+
 struct TestDiagnosticFilterPass
     : public PassWrapper<TestDiagnosticFilterPass, OperationPass<FuncOp>> {
   StringRef getArgument() const final { return "test-diagnostic-filter"; }
@@ -63,6 +99,7 @@
 namespace test {
 void registerTestDiagnosticsPass() {
   PassRegistration<TestDiagnosticFilterPass>{};
+  PassRegistration<TestDiagnosticInspectorPass>{};
 }
 } // namespace test
 } // namespace mlir