4 files changed, 53 insertions, 23 deletions

diff --git a/source/slang/slang-compiler.h b/source/slang/slang-compiler.h
index 14ac63531..07e611355 100755
--- a/source/slang/slang-compiler.h
+++ b/source/slang/slang-compiler.h
@@ -1366,14 +1366,6 @@ namespace Slang
             ///
         void setIRModule(IRModule* irModule) { m_irModule = irModule; }
 
-        DigestBuilder& getContentsDigestBuilder() { return contentsBuilder; }
-
-            /// Set the contents digest for this module.
-        void setContentsDigest(slang::Digest digest) { contentsDigest = digest; }
-
-            /// Get the contents digest for this module.
-        slang::Digest getContentsDigest() { return contentsDigest; }
-
         Index getEntryPointCount() SLANG_OVERRIDE { return 0; }
         RefPtr<EntryPoint> getEntryPoint(Index index) SLANG_OVERRIDE { SLANG_UNUSED(index); return nullptr; }
         String getEntryPointMangledName(Index index) SLANG_OVERRIDE { SLANG_UNUSED(index); return String(); }
@@ -1483,7 +1475,7 @@ namespace Slang
         StringSlicePool m_mangledExportPool;
         List<NodeBase*> m_mangledExportSymbols;
 
-        DigestBuilder contentsBuilder;
+        slang::Digest lastModifiedDigest;
         slang::Digest contentsDigest;
     };
     typedef Module LoadedModule;
diff --git a/source/slang/slang-preprocessor.cpp b/source/slang/slang-preprocessor.cpp
index c977e44ab..fca8f5029 100644
--- a/source/slang/slang-preprocessor.cpp
+++ b/source/slang/slang-preprocessor.cpp
@@ -32,10 +32,9 @@ void PreprocessorHandler::handleEndOfTranslationUnit(Preprocessor* preprocessor)
     SLANG_UNUSED(preprocessor);
 }
 
-void PreprocessorHandler::handleFileDependency(String const& path, ISlangBlob* contents)
+void PreprocessorHandler::handleFileDependency(String const& path)
 {
     SLANG_UNUSED(path);
-    SLANG_UNUSED(contents);
 }
 
 // In order to simplify the naming scheme, we will nest the implementaiton of the
@@ -2973,7 +2972,7 @@ static SlangResult readFile(
     //
     if( auto handler = context->m_preprocessor->handler )
     {
-        handler->handleFileDependency(path, *outBlob);
+        handler->handleFileDependency(path);
     }
 
     return SLANG_OK;
diff --git a/source/slang/slang-preprocessor.h b/source/slang/slang-preprocessor.h
index 90e03e964..4d7721d31 100644
--- a/source/slang/slang-preprocessor.h
+++ b/source/slang/slang-preprocessor.h
@@ -28,7 +28,7 @@ using preprocessor::Preprocessor;
 struct PreprocessorHandler
 {
     virtual void handleEndOfTranslationUnit(Preprocessor* preprocessor);
-    virtual void handleFileDependency(String const& path, ISlangBlob* contents = nullptr);
+    virtual void handleFileDependency(String const& path);
 };
 
     /// Description of a preprocessor options/dependencies
diff --git a/source/slang/slang.cpp b/source/slang/slang.cpp
index 361f1b193..5add881d6 100644
--- a/source/slang/slang.cpp
+++ b/source/slang/slang.cpp
@@ -49,6 +49,8 @@
 
 #include "../../slang-tag-version.h"
 
+#include <sys/stat.h>
+
 // Used to print exception type names in internal-compiler-error messages
 #include <typeinfo>
 
@@ -1898,13 +1900,9 @@ protected:
     // by applications to decide when they need to "hot reload"
     // their shader code.
     //
-    void handleFileDependency(String const& path, ISlangBlob* sourceBlob) SLANG_OVERRIDE
+    void handleFileDependency(String const& path) SLANG_OVERRIDE
     {
         m_module->addFilePathDependency(path);
-        if (sourceBlob)
-        {
-            m_module->getContentsDigestBuilder().addToDigest(sourceBlob);
-        }
     }
 
     // The second task that this handler deals with is detecting
@@ -3046,10 +3044,6 @@ RefPtr<Module> Linkage::loadModule(
         return nullptr;
     }
 
-    auto builder = module->getContentsDigestBuilder();
-    builder.addToDigest(sourceBlob);
-    module->setContentsDigest(builder.finalize());
-
     return module;
 }
 
@@ -3269,7 +3263,52 @@ void Module::updateDependencyBasedHash(
 
 void Module::updateContentsBasedHash(DigestBuilder& builder)
 {
-    builder.addToDigest(getContentsDigest());
+    auto filePathDependencies = getFilePathDependencies();
+
+    DigestBuilder lastModifiedBuilder;
+    auto statFailed = false;
+    for (auto file : filePathDependencies)
+    {
+        struct stat fileStatus;
+        auto res = stat(file.getBuffer(), &fileStatus);
+        if (res != 0)
+        {
+            statFailed = true;
+            break;
+        }
+        lastModifiedBuilder.addToDigest(fileStatus.st_mtime);
+    }
+
+    slang::Digest temp = lastModifiedBuilder.finalize();
+    if (statFailed || temp != lastModifiedDigest)
+    {
+        // Either a stat() call failed, or changes were made to at least one of the file dependencies,
+        // so we will need to re-generate the contents digest and save the new digest.
+        DigestBuilder contentsBuilder;
+        for (auto file : filePathDependencies)
+        {
+            List<uint8_t> fileContents;
+            if (SLANG_FAILED(File::readAllBytes(file, fileContents)))
+            {
+                // Failure to read the file means this is a digest for the contents of a source
+                // file which does not live on disk.
+                contentsBuilder.addToDigest(DigestUtil::fromString(file.getUnownedSlice()));
+            }
+            else
+            {
+                contentsBuilder.addToDigest(fileContents);
+            }
+        }
+        contentsDigest = contentsBuilder.finalize();
+        if (!statFailed)
+        {
+            // If no stat() calls failed, then we have a valid last modified digest and should
+            // update the one we have saved.
+            lastModifiedDigest = temp;
+        }
+    }
+
+    builder.addToDigest(contentsDigest);
 }
 
 void Module::addModuleDependency(Module* module)