Make getHeaderSnippet into an internal API

sdk/src/org.graalvm.nativeimage/snapshot.sigtest

@@ -369,7 +369,6 @@ meth public boolean isInConfiguration()
 meth public java.util.List<java.lang.String> getHeaderFiles()
 meth public java.util.List<java.lang.String> getLibraries()
 meth public java.util.List<java.lang.String> getLibraryPaths()
-meth public java.util.List<java.lang.String> getHeaderSnippet()
 meth public java.util.List<java.lang.String> getMacroDefinitions()
 meth public java.util.List<java.lang.String> getOptions()
 

sdk/src/org.graalvm.nativeimage/src/org/graalvm/nativeimage/c/CContext.java

@@ -134,15 +134,5 @@ default List<String> getLibraries() {
         default List<String> getLibraryPaths() {
             return Collections.emptyList();
         }
-
-        /**
-         * Returns a C header file snippet that should be injected into the query code that gets
-         * generated for this CContext.
-         *
-         * @since 20.3
-         */
-        default List<String> getHeaderSnippet() {
-            return Collections.emptyList();
-        }
     }
 }

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/c/BuiltinDirectives.java

@@ -26,11 +26,9 @@
 
 import java.util.List;
 
-import org.graalvm.nativeimage.c.CContext;
-
 import com.oracle.svm.core.c.function.GraalIsolateHeader;
 
-public class BuiltinDirectives implements CContext.Directives {
+public class BuiltinDirectives implements DirectivesExtension {
     @Override
     public List<String> getHeaderSnippet() {
         return GraalIsolateHeader.getGraalIsolatePreamble();

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/c/DirectivesExtension.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2020, 2020, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package com.oracle.svm.hosted.c;
+
+import java.util.Collections;
+import java.util.List;
+
+import org.graalvm.nativeimage.c.CContext;
+
+public interface DirectivesExtension extends CContext.Directives {
+
+    /**
+     * Returns a C header file snippet that should be injected into the query code that gets
+     * generated for this CContext.
+     *
+     */
+    default List<String> getHeaderSnippet() {
+        return Collections.emptyList();
+    }
+}

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/c/codegen/QueryCodeWriter.java

@@ -33,7 +33,9 @@
 import java.util.List;
 
 import org.graalvm.nativeimage.Platform;
+import org.graalvm.nativeimage.c.CContext;
 
+import com.oracle.svm.hosted.c.DirectivesExtension;
 import com.oracle.svm.hosted.c.info.ConstantInfo;
 import com.oracle.svm.hosted.c.info.ElementInfo;
 import com.oracle.svm.hosted.c.info.EnumConstantInfo;
@@ -106,8 +108,10 @@ public String getLine(int lineNumber) {
 
     @Override
     protected void visitNativeCodeInfo(NativeCodeInfo nativeCodeInfo) {
+        CContext.Directives directives = nativeCodeInfo.getDirectives();
+
         /* Write general macro definitions. */
-        List<String> macroDefinitions = nativeCodeInfo.getDirectives().getMacroDefinitions();
+        List<String> macroDefinitions = directives.getMacroDefinitions();
         if (!macroDefinitions.isEmpty()) {
             macroDefinitions.forEach(writer::appendMacroDefinition);
             writer.appendln();
@@ -129,14 +133,16 @@ protected void visitNativeCodeInfo(NativeCodeInfo nativeCodeInfo) {
         }
 
         /* Inject CContext specific C header file snippet. */
-        List<String> headerSnippet = nativeCodeInfo.getDirectives().getHeaderSnippet();
-        if (!headerSnippet.isEmpty()) {
-            headerSnippet.forEach(writer::appendln);
-            writer.appendln();
+        if (directives instanceof DirectivesExtension) {
+            List<String> headerSnippet = ((DirectivesExtension) directives).getHeaderSnippet();
+            if (!headerSnippet.isEmpty()) {
+                headerSnippet.forEach(writer::appendln);
+                writer.appendln();
+            }
         }
 
         /* CContext specific header file inclusions. */
-        List<String> headerFiles = nativeCodeInfo.getDirectives().getHeaderFiles();
+        List<String> headerFiles = directives.getHeaderFiles();
         if (!headerFiles.isEmpty()) {
             writer.includeFiles(headerFiles);
             writer.appendln();

substratevm/src/org.graalvm.polyglot.nativeapi/src/org/graalvm/polyglot/nativeapi/PolyglotNativeAPICContext.java

@@ -27,11 +27,10 @@
 import java.util.Collections;
 import java.util.List;
 
-import org.graalvm.nativeimage.c.CContext.Directives;
-
 import com.oracle.svm.core.c.function.GraalIsolateHeader;
+import com.oracle.svm.hosted.c.DirectivesExtension;
 
-public class PolyglotNativeAPICContext implements Directives {
+public class PolyglotNativeAPICContext implements DirectivesExtension {
 
     @Override
     public List<String> getHeaderFiles() {