diff --git a/StandAlone/StandAlone.cpp b/StandAlone/StandAlone.cpp
index e914150d..8eb3ee3e 100644
--- a/StandAlone/StandAlone.cpp
+++ b/StandAlone/StandAlone.cpp
@@ -701,8 +701,8 @@ void CompileAndLinkShaders()
         shader->setStrings(shaderStrings, 1);
         if (Options & EOptionOutputPreprocessed) {
             std::string str;
-            if (shader->preprocess(&Resources, defaultVersion, ENoProfile,
-                                   false, false, messages, &str)) {
+            if (shader->preprocess(&Resources, defaultVersion, ENoProfile, false, false,
+                                   messages, &str, glslang::TShader::ForbidInclude())) {
                 PutsIfNonEmpty(str.c_str());
             } else {
                 CompileFailed = true;
diff --git a/Test/baseResults/preprocessor.include.disabled.vert.err b/Test/baseResults/preprocessor.include.disabled.vert.err
new file mode 100644
index 00000000..1145a314
--- /dev/null
+++ b/Test/baseResults/preprocessor.include.disabled.vert.err
@@ -0,0 +1,13 @@
+ERROR: 0:8000: '#include' : required extension not requested: GL_GOOGLE_include_directive
+ERROR: 0:8000: '#include' : must be followed by a file designation
+ERROR: 0:8001: '#include' : required extension not requested: GL_GOOGLE_include_directive
+ERROR: 0:8001: '#include' : must be followed by a file designation
+ERROR: 0:8002: '#include' : required extension not requested: GL_GOOGLE_include_directive
+ERROR: 0:8002: '#include' : unexpected include directive
+ERROR: 0:8003: '#include' : required extension not requested: GL_GOOGLE_include_directive
+ERROR: 0:8003: '#include' : extra content after file designation
+ERROR: 0:8004: '#include' : required extension not requested: GL_GOOGLE_include_directive
+ERROR: 0:8004: '#include' : unexpected include directive
+ERROR: 10 compilation errors.  No code generated.
+
+
diff --git a/Test/baseResults/preprocessor.include.disabled.vert.out b/Test/baseResults/preprocessor.include.disabled.vert.out
new file mode 100644
index 00000000..e69de29b
diff --git a/Test/baseResults/preprocessor.include.enabled.vert.err b/Test/baseResults/preprocessor.include.enabled.vert.err
new file mode 100644
index 00000000..2cdf3f28
--- /dev/null
+++ b/Test/baseResults/preprocessor.include.enabled.vert.err
@@ -0,0 +1,8 @@
+ERROR: 0:8000: '#include' : must be followed by a file designation
+ERROR: 0:8001: '#include' : must be followed by a file designation
+ERROR: 0:8002: '#include' : unexpected include directive
+ERROR: 0:8003: '#include' : extra content after file designation
+ERROR: 0:8004: '#include' : unexpected include directive
+ERROR: 5 compilation errors.  No code generated.
+
+
diff --git a/Test/baseResults/preprocessor.include.enabled.vert.out b/Test/baseResults/preprocessor.include.enabled.vert.out
new file mode 100644
index 00000000..e69de29b
diff --git a/Test/preprocessor.include.disabled.vert b/Test/preprocessor.include.disabled.vert
new file mode 100644
index 00000000..130d928e
--- /dev/null
+++ b/Test/preprocessor.include.disabled.vert
@@ -0,0 +1,7 @@
+#line 8000
+#include
+#include 123
+#include "foo"
+#include "foo" garbage
+#include "no-eol"
+
diff --git a/Test/preprocessor.include.enabled.vert b/Test/preprocessor.include.enabled.vert
new file mode 100644
index 00000000..ecdf466e
--- /dev/null
+++ b/Test/preprocessor.include.enabled.vert
@@ -0,0 +1,7 @@
+#extension GL_GOOGLE_include_directive : enable
+#line 8000
+#include
+#include 123
+#include "foo"
+#include "foo" garbage
+#include "no-eol"
diff --git a/Test/test-preprocessor-list b/Test/test-preprocessor-list
index e75ac1b4..cd2381a5 100644
--- a/Test/test-preprocessor-list
+++ b/Test/test-preprocessor-list
@@ -4,6 +4,8 @@ preprocessor.edge_cases.vert
 preprocessor.errors.vert
 preprocessor.extensions.vert
 preprocessor.function_macro.vert
+preprocessor.include.enabled.vert
+preprocessor.include.disabled.vert
 preprocessor.line.vert
 preprocessor.line.frag
 preprocessor.pragma.vert
diff --git a/glslang/MachineIndependent/ParseHelper.h b/glslang/MachineIndependent/ParseHelper.h
index 6f5645ef..e008c0f2 100644
--- a/glslang/MachineIndependent/ParseHelper.h
+++ b/glslang/MachineIndependent/ParseHelper.h
@@ -214,9 +214,11 @@ public:
     int getNumErrors() const { return numErrors; }
     const TSourceLoc& getCurrentLoc() const { return currentScanner->getSourceLoc(); }
     void setCurrentLine(int line) { currentScanner->setLine(line); }
+    void setCurrentColumn(int col) { currentScanner->setColumn(col); }
     void setCurrentSourceName(const char* name) { currentScanner->setFile(name); }
     void setCurrentString(int string) { currentScanner->setString(string); }
     void setScanner(TInputScanner* scanner) { currentScanner  = scanner; }
+    TInputScanner* getScanner() const { return currentScanner; }
 
     bool lineDirectiveShouldSetNextLine() const;
 
@@ -235,6 +237,7 @@ public:
     void checkDeprecated(const TSourceLoc&, int queryProfiles, int depVersion, const char* featureDesc);
     void requireNotRemoved(const TSourceLoc&, int queryProfiles, int removedVersion, const char* featureDesc);
     void requireExtensions(const TSourceLoc&, int numExtensions, const char* const extensions[], const char* featureDesc);
+    void ppRequireExtensions(const TSourceLoc&, int numExtensions, const char* const extensions[], const char* featureDesc);
     TExtensionBehavior getExtensionBehavior(const char*);
     bool extensionTurnedOn(const char* const extension);
     bool extensionsTurnedOn(int numExtensions, const char* const extensions[]);
@@ -250,13 +253,14 @@ public:
 
 protected:
     void nonInitConstCheck(const TSourceLoc&, TString& identifier, TType& type);
-	void inheritGlobalDefaults(TQualifier& dst) const;
+    void inheritGlobalDefaults(TQualifier& dst) const;
     TVariable* makeInternalVariable(const char* name, const TType&) const;
     TVariable* declareNonArray(const TSourceLoc&, TString& identifier, TType&, bool& newDeclaration);
     void declareArray(const TSourceLoc&, TString& identifier, const TType&, TSymbol*&, bool& newDeclaration);
     TIntermNode* executeInitializer(const TSourceLoc&, TIntermTyped* initializer, TVariable* variable);
     TIntermTyped* convertInitializerList(const TSourceLoc&, const TType&, TIntermTyped* initializer);
     TOperator mapTypeToConstructorOp(const TType&) const;
+    bool checkExtensionsRequested(const TSourceLoc&, int numExtensions, const char* const extensions[], const char* featureDesc);
     void updateExtensionBehavior(const char* const extension, TExtensionBehavior);
     void finalErrorCheck();
     void outputMessage(const TSourceLoc&, const char* szReason, const char* szToken,
diff --git a/glslang/MachineIndependent/Scan.h b/glslang/MachineIndependent/Scan.h
index ff7bfa2f..eade05fd 100644
--- a/glslang/MachineIndependent/Scan.h
+++ b/glslang/MachineIndependent/Scan.h
@@ -154,6 +154,9 @@ public:
         loc[getLastValidSourceIndex()].name = nullptr;
     }
 
+    // for #include content indentation
+    void setColumn(int col) { loc[getLastValidSourceIndex()].column = col; }
+
     const TSourceLoc& getSourceLoc() const { return loc[std::max(0, std::min(currentSource, numSources - finale - 1))]; }
     // Returns the index (starting from 0) of the most recent valid source string we are reading from.
     int getLastValidSourceIndex() const { return std::min(currentSource, numSources - 1); }
diff --git a/glslang/MachineIndependent/ShaderLang.cpp b/glslang/MachineIndependent/ShaderLang.cpp
index e98df614..617f9e21 100644
--- a/glslang/MachineIndependent/ShaderLang.cpp
+++ b/glslang/MachineIndependent/ShaderLang.cpp
@@ -130,7 +130,7 @@ bool InitializeSymbolTable(const TString& builtIns, int version, EProfile profil
     TIntermediate intermediate(language, version, profile);
     
     TParseContext parseContext(symbolTable, intermediate, true, version, profile, language, infoSink);
-    TPpContext ppContext(parseContext);
+    TPpContext ppContext(parseContext, TShader::ForbidInclude());
     TScanContext scanContext(parseContext);
     parseContext.setScanContext(&scanContext);
     parseContext.setPpContext(&ppContext);
@@ -463,7 +463,8 @@ bool ProcessDeferred(
     EShMessages messages,       // warnings/errors/AST; things to print out
     TIntermediate& intermediate, // returned tree, etc.
     ProcessingContext& processingContext,
-    bool requireNonempty
+    bool requireNonempty,
+    const TShader::Includer& includer
     )
 {
     if (! InitThread())
@@ -565,7 +566,7 @@ bool ProcessDeferred(
 
     TParseContext parseContext(symbolTable, intermediate, false, version, profile, compiler->getLanguage(), compiler->infoSink, forwardCompatible, messages);
     glslang::TScanContext scanContext(parseContext);
-    TPpContext ppContext(parseContext);
+    TPpContext ppContext(parseContext, includer);
     parseContext.setScanContext(&scanContext);
     parseContext.setPpContext(&ppContext);
     parseContext.setLimits(*resources);
@@ -838,6 +839,7 @@ bool PreprocessDeferred(
     bool forceDefaultVersionAndProfile,
     bool forwardCompatible,     // give errors for use of deprecated features
     EShMessages messages,       // warnings/errors/AST; things to print out
+    const TShader::Includer& includer,
     TIntermediate& intermediate, // returned tree, etc.
     std::string* outputString)
 {
@@ -845,7 +847,8 @@ bool PreprocessDeferred(
     return ProcessDeferred(compiler, shaderStrings, numStrings, inputLengths, stringNames,
                            preamble, optLevel, resources, defaultVersion,
                            defaultProfile, forceDefaultVersionAndProfile,
-                           forwardCompatible, messages, intermediate, parser, false);
+                           forwardCompatible, messages, intermediate, parser,
+                           false, includer);
 }
 
 
@@ -874,13 +877,15 @@ bool CompileDeferred(
     bool forceDefaultVersionAndProfile,
     bool forwardCompatible,     // give errors for use of deprecated features
     EShMessages messages,       // warnings/errors/AST; things to print out
-    TIntermediate& intermediate) // returned tree, etc.
+    TIntermediate& intermediate,// returned tree, etc.
+    const TShader::Includer& includer)
 {
     DoFullParse parser;
     return ProcessDeferred(compiler, shaderStrings, numStrings, inputLengths, stringNames,
                            preamble, optLevel, resources, defaultVersion,
                            defaultProfile, forceDefaultVersionAndProfile,
-                           forwardCompatible, messages, intermediate, parser, true);
+                           forwardCompatible, messages, intermediate, parser,
+                           true, includer);
 }
 
 } // end anonymous namespace for local functions
@@ -1024,7 +1029,7 @@ int ShCompile(
     TIntermediate intermediate(compiler->getLanguage());
     bool success = CompileDeferred(compiler, shaderStrings, numStrings, inputLengths, nullptr,
                                    "", optLevel, resources, defaultVersion, ENoProfile, false,
-                                   forwardCompatible, messages, intermediate);
+                                   forwardCompatible, messages, intermediate, TShader::ForbidInclude());
 
     //
     // Call the machine dependent compiler
@@ -1327,7 +1332,7 @@ void TShader::setStringsWithLengthsAndNames(
 // Returns true for success.
 //
 bool TShader::parse(const TBuiltInResource* builtInResources, int defaultVersion, EProfile defaultProfile, bool forceDefaultVersionAndProfile,
-                    bool forwardCompatible, EShMessages messages)
+                    bool forwardCompatible, EShMessages messages, const Includer& includer)
 {
     if (! InitThread())
         return false;
@@ -1340,7 +1345,7 @@ bool TShader::parse(const TBuiltInResource* builtInResources, int defaultVersion
     return CompileDeferred(compiler, strings, numStrings, lengths, stringNames,
                            preamble, EShOptNone, builtInResources, defaultVersion,
                            defaultProfile, forceDefaultVersionAndProfile,
-                           forwardCompatible, messages, *intermediate);
+                           forwardCompatible, messages, *intermediate, includer);
 }
 
 bool TShader::parse(const TBuiltInResource* builtInResources, int defaultVersion, bool forwardCompatible, EShMessages messages)
@@ -1351,9 +1356,11 @@ bool TShader::parse(const TBuiltInResource* builtInResources, int defaultVersion
 // Fill in a string with the result of preprocessing ShaderStrings
 // Returns true if all extensions, pragmas and version strings were valid.
 bool TShader::preprocess(const TBuiltInResource* builtInResources,
-                         int defaultVersion, EProfile defaultProfile, bool forceDefaultVersionAndProfile,
-                         bool forwardCompatible,
-                         EShMessages message, std::string* output_string)
+                         int defaultVersion, EProfile defaultProfile,
+                         bool forceDefaultVersionAndProfile,
+                         bool forwardCompatible, EShMessages message,
+                         std::string* output_string,
+                         const TShader::Includer& includer)
 {
     if (! InitThread())
         return false;
@@ -1366,7 +1373,7 @@ bool TShader::preprocess(const TBuiltInResource* builtInResources,
     return PreprocessDeferred(compiler, strings, numStrings, lengths, stringNames, preamble,
                               EShOptNone, builtInResources, defaultVersion,
                               defaultProfile, forceDefaultVersionAndProfile,
-                              forwardCompatible, message, *intermediate, output_string);
+                              forwardCompatible, message, includer, *intermediate, output_string);
 }
 
 const char* TShader::getInfoLog()
diff --git a/glslang/MachineIndependent/Versions.cpp b/glslang/MachineIndependent/Versions.cpp
index 28ad10cb..c751076f 100644
--- a/glslang/MachineIndependent/Versions.cpp
+++ b/glslang/MachineIndependent/Versions.cpp
@@ -174,7 +174,9 @@ void TParseContext::initializeExtensionBehavior()
     extensionBehavior[E_GL_ARB_viewport_array]               = EBhDisable;
 //    extensionBehavior[E_GL_ARB_cull_distance]                = EBhDisable;    // present for 4.5, but need extension control over block members
 
+    // #line and #include
     extensionBehavior[E_GL_GOOGLE_cpp_style_line_directive]          = EBhDisable;
+    extensionBehavior[E_GL_GOOGLE_include_directive]                 = EBhDisable;
 
     // AEP
     extensionBehavior[E_GL_ANDROID_extension_pack_es31a]             = EBhDisablePartial;
@@ -219,7 +221,9 @@ const char* TParseContext::getPreamble()
             "#define GL_OES_EGL_image_external 1\n"
             "#define GL_EXT_shader_texture_lod 1\n"
 
+            // #line and #include
             "#define GL_GOOGLE_cpp_style_line_directive 1\n"
+            "#define GL_GOOGLE_include_directive 1\n"
 
             // AEP
             "#define GL_ANDROID_extension_pack_es31a 1\n"
@@ -270,6 +274,7 @@ const char* TParseContext::getPreamble()
             "#define GL_ARB_viewport_array 1\n"
 
             "#define GL_GOOGLE_cpp_style_line_directive 1\n"
+            "#define GL_GOOGLE_include_directive 1\n"
 //            "#define GL_ARB_cull_distance 1\n"    // present for 4.5, but need extension control over block members
             ;
     }
@@ -406,17 +411,15 @@ void TParseContext::requireNotRemoved(const TSourceLoc& loc, int profileMask, in
     }
 }
 
-//
-// Use when there are no profile/version to check, it's just an error if one of the
-// extensions is not present.
-//
-void TParseContext::requireExtensions(const TSourceLoc& loc, int numExtensions, const char* const extensions[], const char* featureDesc)
+// Returns true if at least one of the extensions in the extensions parameter is requested. Otherwise, returns false.
+// Warns appropriately if the requested behavior of an extension is "warn".
+bool TParseContext::checkExtensionsRequested(const TSourceLoc& loc, int numExtensions, const char* const extensions[], const char* featureDesc)
 {
     // First, see if any of the extensions are enabled
     for (int i = 0; i < numExtensions; ++i) {
         TExtensionBehavior behavior = getExtensionBehavior(extensions[i]);
         if (behavior == EBhEnable || behavior == EBhRequire)
-            return;
+            return true;
     }
 
     // See if any extensions want to give a warning on use; give warnings for all such extensions
@@ -433,7 +436,17 @@ void TParseContext::requireExtensions(const TSourceLoc& loc, int numExtensions,
         }
     }
     if (warned)
-        return;
+        return true;
+    return false;
+}
+
+//
+// Use when there are no profile/version to check, it's just an error if one of the
+// extensions is not present.
+//
+void TParseContext::requireExtensions(const TSourceLoc& loc, int numExtensions, const char* const extensions[], const char* featureDesc)
+{
+    if (checkExtensionsRequested(loc, numExtensions, extensions, featureDesc)) return;
 
     // If we get this far, give errors explaining what extensions are needed
     if (numExtensions == 1)
@@ -445,6 +458,24 @@ void TParseContext::requireExtensions(const TSourceLoc& loc, int numExtensions,
     }
 }
 
+//
+// Use by preprocessor when there are no profile/version to check, it's just an error if one of the
+// extensions is not present.
+//
+void TParseContext::ppRequireExtensions(const TSourceLoc& loc, int numExtensions, const char* const extensions[], const char* featureDesc)
+{
+    if (checkExtensionsRequested(loc, numExtensions, extensions, featureDesc)) return;
+
+    // If we get this far, give errors explaining what extensions are needed
+    if (numExtensions == 1)
+        ppError(loc, "required extension not requested:", featureDesc, extensions[0]);
+    else {
+        ppError(loc, "required extension not requested:", featureDesc, "Possible extensions include:");
+        for (int i = 0; i < numExtensions; ++i)
+            infoSink.info.message(EPrefixNone, extensions[i]);
+    }
+}
+
 TExtensionBehavior TParseContext::getExtensionBehavior(const char* extension)
 {
     auto iter = extensionBehavior.find(TString(extension));
@@ -525,6 +556,8 @@ void TParseContext::updateExtensionBehavior(int line, const char* extension, con
         updateExtensionBehavior(line, "GL_EXT_shader_io_blocks", behaviorString);
     else if (strcmp(extension, "GL_OES_tessellation_shader") == 0)
         updateExtensionBehavior(line, "GL_OES_shader_io_blocks", behaviorString);
+    else if (strcmp(extension, "GL_GOOGLE_include_directive") == 0)
+        updateExtensionBehavior(line, "GL_GOOGLE_cpp_style_line_directive", behaviorString);
 }
 
 void TParseContext::updateExtensionBehavior(const char* extension, TExtensionBehavior behavior)
diff --git a/glslang/MachineIndependent/Versions.h b/glslang/MachineIndependent/Versions.h
index ae8fd414..bb3cbc4d 100644
--- a/glslang/MachineIndependent/Versions.h
+++ b/glslang/MachineIndependent/Versions.h
@@ -112,7 +112,9 @@ const char* const E_GL_ARB_shader_texture_image_samples = "GL_ARB_shader_texture
 const char* const E_GL_ARB_viewport_array               = "GL_ARB_viewport_array";
 //const char* const E_GL_ARB_cull_distance            = "GL_ARB_cull_distance";  // present for 4.5, but need extension control over block members
 
+// #line and #include
 const char* const E_GL_GOOGLE_cpp_style_line_directive          = "GL_GOOGLE_cpp_style_line_directive";
+const char* const E_GL_GOOGLE_include_directive                 = "GL_GOOGLE_include_directive";
 
 // AEP
 const char* const E_GL_ANDROID_extension_pack_es31a             = "GL_ANDROID_extension_pack_es31a";
diff --git a/glslang/MachineIndependent/preprocessor/Pp.cpp b/glslang/MachineIndependent/preprocessor/Pp.cpp
index 279706ec..d62b7369 100644
--- a/glslang/MachineIndependent/preprocessor/Pp.cpp
+++ b/glslang/MachineIndependent/preprocessor/Pp.cpp
@@ -83,6 +83,7 @@ NVIDIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include <stdarg.h>
 #include <stdio.h>
+#include <sstream>
 #include <stdlib.h>
 #include <string.h>
 #include <ctype.h>
@@ -596,6 +597,51 @@ int TPpContext::CPPifdef(int defined, TPpToken* ppToken)
     return token;
 }
 
+// Handle #include
+int TPpContext::CPPinclude(TPpToken* ppToken)
+{
+    const TSourceLoc directiveLoc = ppToken->loc;
+    int token = scanToken(ppToken);
+    if (token != PpAtomConstString) {
+        // TODO: handle angle brackets.
+        parseContext.ppError(directiveLoc, "must be followed by a file designation", "#include", "");
+    } else {
+        // Make a copy of the name because it will be overwritten by the next token scan.
+        const std::string filename = ppToken->name;
+        token = scanToken(ppToken);
+        if (token != '\n' && token != EndOfInput) {
+            parseContext.ppError(ppToken->loc, "extra content after file designation", "#include", "");
+        } else {
+            std::string sourceName;
+            std::string replacement;
+            std::tie(sourceName, replacement) = includer.include(filename.c_str());
+            if (!sourceName.empty()) {
+                if (!replacement.empty()) {
+                    const bool forNextLine = parseContext.lineDirectiveShouldSetNextLine();
+                    std::ostringstream content;
+                    content << "#line " << forNextLine << " " << "\"" << sourceName << "\"\n";
+                    content << replacement << (replacement.back() == '\n' ? "" : "\n");
+                    content << "#line " << directiveLoc.line + forNextLine << " ";
+                    if (directiveLoc.name != nullptr) {
+                        content << "\"" << directiveLoc.name << "\"";
+                    } else {
+                        content << directiveLoc.string;
+                    }
+                    content << "\n";
+                    pushInput(new TokenizableString(directiveLoc, content.str(), this));
+                }
+                // At EOF, there's no "current" location anymore.
+                if (token != EndOfInput) parseContext.setCurrentColumn(0);
+                // Don't accidentally return EndOfInput, which will end all preprocessing.
+                return '\n';
+            } else {
+                parseContext.ppError(directiveLoc, replacement.c_str(), "#include", "");
+            }
+        }
+    }
+    return token;
+}
+
 // Handle #line
 int TPpContext::CPPline(TPpToken* ppToken) 
 {
@@ -629,7 +675,7 @@ int TPpContext::CPPline(TPpToken* ppToken)
 
         if (token != '\n') {
             if (token == PpAtomConstString) {
-                parseContext.requireExtensions(directiveLoc, 1, &E_GL_GOOGLE_cpp_style_line_directive, "filename-based #line");
+                parseContext.ppRequireExtensions(directiveLoc, 1, &E_GL_GOOGLE_cpp_style_line_directive, "filename-based #line");
                 // We need to save a copy of the string instead of pointing
                 // to the name field of the token since the name field
                 // will likely be overwritten by the next token scan.
@@ -845,6 +891,10 @@ int TPpContext::readCPPline(TPpToken* ppToken)
         case PpAtomIfndef:
             token = CPPifdef(0, ppToken);
             break;
+        case PpAtomInclude:
+            parseContext.ppRequireExtensions(ppToken->loc, 1, &E_GL_GOOGLE_include_directive, "#include");
+            token = CPPinclude(ppToken);
+            break;
         case PpAtomLine:
             token = CPPline(ppToken);
             break;
@@ -967,7 +1017,7 @@ int TPpContext::MacroExpand(int atom, TPpToken* ppToken, bool expandUndef, bool
 
     case PpAtomFileMacro: {
         if (const char* current_file = parseContext.getCurrentLoc().name) {
-            parseContext.requireExtensions(ppToken->loc, 1, &E_GL_GOOGLE_cpp_style_line_directive, "filename-based __FILE__");
+            parseContext.ppRequireExtensions(ppToken->loc, 1, &E_GL_GOOGLE_cpp_style_line_directive, "filename-based __FILE__");
             sprintf(ppToken->name, "\"%s\"", current_file);
         } else {
             ppToken->ival = parseContext.getCurrentLoc().string;
diff --git a/glslang/MachineIndependent/preprocessor/PpAtom.cpp b/glslang/MachineIndependent/preprocessor/PpAtom.cpp
index 04e0d630..b3cb2b07 100644
--- a/glslang/MachineIndependent/preprocessor/PpAtom.cpp
+++ b/glslang/MachineIndependent/preprocessor/PpAtom.cpp
@@ -120,6 +120,9 @@ const struct {
     { PpAtomLineMacro,       "__LINE__" },
     { PpAtomFileMacro,       "__FILE__" },
     { PpAtomVersionMacro,    "__VERSION__" },
+
+    { PpAtomInclude,        "include" },
+
 };
 
 } // end anonymous namespace
diff --git a/glslang/MachineIndependent/preprocessor/PpContext.cpp b/glslang/MachineIndependent/preprocessor/PpContext.cpp
index 828764b0..b8d2c737 100644
--- a/glslang/MachineIndependent/preprocessor/PpContext.cpp
+++ b/glslang/MachineIndependent/preprocessor/PpContext.cpp
@@ -83,8 +83,8 @@ NVIDIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 namespace glslang {
 
-TPpContext::TPpContext(TParseContext& pc) : 
-    preamble(0), strings(0), parseContext(pc), inComment(false)
+TPpContext::TPpContext(TParseContext& pc, const TShader::Includer& inclr) : 
+    preamble(0), strings(0), parseContext(pc), includer(inclr), inComment(false)
 {
     InitAtomTable();
     InitScanner();
diff --git a/glslang/MachineIndependent/preprocessor/PpContext.h b/glslang/MachineIndependent/preprocessor/PpContext.h
index 74a9f5dd..5d06e701 100644
--- a/glslang/MachineIndependent/preprocessor/PpContext.h
+++ b/glslang/MachineIndependent/preprocessor/PpContext.h
@@ -118,7 +118,7 @@ class TInputScanner;
 // Don't expect too much in terms of OO design.
 class TPpContext {
 public:
-    TPpContext(TParseContext&);
+    TPpContext(TParseContext&, const TShader::Includer&);
     virtual ~TPpContext();
 
     void setPreamble(const char* preamble, size_t length);
@@ -134,6 +134,10 @@ public:
         virtual int getch() = 0;
         virtual void ungetch() = 0;
 
+        // Will be called when we start reading tokens from this instance
+        virtual void notifyActivated() {}
+        // Will be called when we do not read tokens from this instance anymore
+        virtual void notifyDeleted() {}
     protected:
         bool done;
         TPpContext* pp;
@@ -144,9 +148,11 @@ public:
     void pushInput(tInput* in)
     {
         inputStack.push_back(in);
+        in->notifyActivated();
     }
     void popInput()
     {
+        inputStack.back()->notifyDeleted();
         delete inputStack.back();
         inputStack.pop_back();
     }
@@ -281,6 +287,8 @@ protected:
     // from Pp.cpp
     //
     TSourceLoc ifloc; /* outermost #if */
+    // Used to obtain #include content.
+    const TShader::Includer& includer;
 
     int InitCPP();
     int CPPdefine(TPpToken * ppToken);
@@ -291,6 +299,7 @@ protected:
     int evalToToken(int token, bool shortCircuit, int& res, bool& err, TPpToken * ppToken);
     int CPPif (TPpToken * ppToken); 
     int CPPifdef(int defined, TPpToken * ppToken);
+    int CPPinclude(TPpToken * ppToken);
     int CPPline(TPpToken * ppToken); 
     int CPPerror(TPpToken * ppToken); 
     int CPPpragma(TPpToken * ppToken);
@@ -419,6 +428,51 @@ protected:
         TInputScanner* input;
     };
 
+    // Holds a string that can be tokenized via the tInput interface.
+    class TokenizableString : public tInput {
+    public:
+        // Copies str, which must be non-empty.
+        TokenizableString(const TSourceLoc& startLoc, const std::string& str, TPpContext* pp)
+            : tInput(pp),
+              str_(str),
+              strings(str_.data()),
+              length(str_.size()),
+              scanner(1, &strings, &length),
+              prevScanner(nullptr),
+              stringInput(pp, scanner) {
+                  scanner.setLine(startLoc.line);
+                  scanner.setString(startLoc.string);
+                  scanner.setFile(startLoc.name);
+        }
+
+        // tInput methods:
+        int scan(TPpToken* t) override { return stringInput.scan(t); }
+        int getch() override { return stringInput.getch(); }
+        void ungetch() override { stringInput.ungetch(); }
+
+        void notifyActivated() override
+        {
+            prevScanner = pp->parseContext.getScanner();
+            pp->parseContext.setScanner(&scanner);
+        }
+        void notifyDeleted() override { pp->parseContext.setScanner(prevScanner); }
+
+    private:
+        // Stores the titular string.
+        const std::string str_;
+        // Will point to str_[0] and be passed to scanner constructor.
+        const char* const strings;
+        // Length of str_, passed to scanner constructor.
+        size_t length;
+        // Scans over str_.
+        TInputScanner scanner;
+        // The previous effective scanner before the scanner in this instance
+        // has been activated.
+        TInputScanner* prevScanner;
+        // Delegate object implementing the tInput interface.
+        tStringInput stringInput;
+    };
+
     int InitScanner();
     int ScanFromString(char* s);
     void missingEndifCheck();
diff --git a/glslang/MachineIndependent/preprocessor/PpTokens.h b/glslang/MachineIndependent/preprocessor/PpTokens.h
index 0d116f9b..391b04ad 100644
--- a/glslang/MachineIndependent/preprocessor/PpTokens.h
+++ b/glslang/MachineIndependent/preprocessor/PpTokens.h
@@ -158,6 +158,9 @@ enum EFixedAtoms {
     PpAtomFileMacro,
     PpAtomVersionMacro,
 
+    // #include
+    PpAtomInclude,
+
     PpAtomLast,
 };
 
diff --git a/glslang/Public/ShaderLang.h b/glslang/Public/ShaderLang.h
index edca638c..3fbfe354 100644
--- a/glslang/Public/ShaderLang.h
+++ b/glslang/Public/ShaderLang.h
@@ -249,6 +249,7 @@ SH_IMPORT_EXPORT int ShGetUniformLocation(const ShHandle uniformMap, const char*
 
 #include <list>
 #include <string>
+#include <utility>
 
 class TCompiler;
 class TInfoSink;
@@ -288,14 +289,35 @@ public:
     void setStringsWithLengthsAndNames(
         const char* const* s, const int* l, const char* const* names, int n);
     void setPreamble(const char* s) { preamble = s; }
-    bool parse(const TBuiltInResource*, int defaultVersion, EProfile defaultProfile, bool forceDefaultVersionAndProfile, bool forwardCompatible, EShMessages);
+
+    // Interface to #include handlers.
+    class Includer {
+    public:
+        // On success, returns the full path and content of the file with the given
+        // filename that replaces "#include filename". On failure, returns an empty
+        // string and an error message.
+        virtual std::pair<std::string, std::string> include(const char* filename) const = 0;
+    };
+
+    // Returns an error message for any #include directive.
+    class ForbidInclude : public Includer {
+    public:
+        std::pair<std::string, std::string> include(const char* filename) const override
+        {
+            return std::make_pair<std::string, std::string>("", "unexpected include directive");
+        }
+    };
+
+    bool parse(const TBuiltInResource*, int defaultVersion, EProfile defaultProfile, bool forceDefaultVersionAndProfile,
+               bool forwardCompatible, EShMessages, const Includer& = ForbidInclude());
+
     // Equivalent to parse() without a default profile and without forcing defaults.
     // Provided for backwards compatibility.
     bool parse(const TBuiltInResource*, int defaultVersion, bool forwardCompatible, EShMessages);
     bool preprocess(const TBuiltInResource* builtInResources,
                     int defaultVersion, EProfile defaultProfile, bool forceDefaultVersionAndProfile,
-                    bool forwardCompatible,
-                    EShMessages message, std::string* outputString);
+                    bool forwardCompatible, EShMessages message, std::string* outputString,
+                    const TShader::Includer& includer);
 
     const char* getInfoLog();
     const char* getInfoDebugLog();