Support customizing SymbolLookup for tree-sitter native library

Motivation:
- Enable clients to customize the SymbolLookup used for the tree-sitter native library.
  For example, clients can use this capability to embed the tree-sitter native library
  in their JAR, which is a common way to solve the native library distribution problem.

Changes:
- Add interface NativeLibraryLookup.
- Add class ChainedLibraryLookup, which loads NativeLibraryLookup implementations
  using java.util.ServiceLoader and chains the SymbolLookup's returned by them.
- Change TreeSitter.java patch to delegate to ChainedLibraryLookup.
- Update build instructions in README.
- Fix execution of jextract.ps1 script in Windows build.

Result:
- Clients that need to customize the SymbolLookup used for the tree-sitter native library
  no longer need to patch and build java-tree-sitter from source.

Author: odenix

README.md

@@ -15,6 +15,9 @@ Java bindings to the [tree-sitter] parsing library.
 git clone https://github.com/tree-sitter/java-tree-sitter
 cd java-tree-sitter
 git submodule init
+git submodule update
+# build tree-sitter and tree-sitter-java native libraries,
+# for example by replicating the steps in .github/workflows/ci.yml
 mvn test
 ```
 

pom.xml

@@ -81,7 +81,8 @@
               <skip>${jextract.skip}</skip>
               <target name="jextract">
                 <echo level="info">Generating sources using jextract</echo>
-                <exec osfamily="windows" executable="${project.basedir}/scripts/jextract.ps1" failonerror="true">
+                <exec osfamily="windows" executable="powershell" failonerror="true">
+                  <arg value="${project.basedir}/scripts/jextract.ps1"/>
                   <arg value="${project.basedir}"/>
                   <arg value="${project.build.directory}"/>
                 </exec>

scripts/TreeSitter_java.patch

@@ -1,22 +1,13 @@
---- a/generated-sources/jextract/io/github/treesitter/jtreesitter/internal/TreeSitter.java
-+++ b/generated-sources/jextract/io/github/treesitter/jtreesitter/internal/TreeSitter.java
-@@ -55,9 +55,16 @@ public class TreeSitter {
+--- a/target/generated-sources/jextract/io/github/treesitter/jtreesitter/internal/TreeSitter.java	
++++ b/target/generated-sources/jextract/io/github/treesitter/jtreesitter/internal/TreeSitter.java
+@@ -55,9 +55,7 @@
          };
      }
-
+ 
 -    static final SymbolLookup SYMBOL_LOOKUP = SymbolLookup.libraryLookup(System.mapLibraryName("tree-sitter"), LIBRARY_ARENA)
 -            .or(SymbolLookup.loaderLookup())
 -            .or(Linker.nativeLinker().defaultLookup());
-+    static final SymbolLookup SYMBOL_LOOKUP = findLibrary().or(Linker.nativeLinker().defaultLookup());
-+
-+    private static final SymbolLookup findLibrary() {
-+        try {
-+            String library = System.mapLibraryName("tree-sitter");
-+            return SymbolLookup.libraryLookup(library, LIBRARY_ARENA);
-+        } catch (IllegalArgumentException e) {
-+            return SymbolLookup.loaderLookup();
-+        }
-+    }
-
++    static final SymbolLookup SYMBOL_LOOKUP = new ChainedLibraryLookup().get(LIBRARY_ARENA);
+ 
      public static final ValueLayout.OfBoolean C_BOOL = ValueLayout.JAVA_BOOLEAN;
      public static final ValueLayout.OfByte C_CHAR = ValueLayout.JAVA_BYTE;

src/main/java/io/github/treesitter/jtreesitter/NativeLibraryLookup.java

@@ -0,0 +1,21 @@
+package io.github.treesitter.jtreesitter;
+
+import java.lang.foreign.Arena;
+import java.lang.foreign.SymbolLookup;
+
+/**
+ * An interface implemented by clients that wish to customize the {@link SymbolLookup} used for the tree-sitter
+ * native library. Implementation classes must be registered by listing their fully qualified class name
+ * in a resource file named {@code META-INF/services/io.github.treesitter.jtreesitter.NativeLibraryLookup}.
+ *
+ * @see java.util.ServiceLoader
+ */
+public interface NativeLibraryLookup {
+    /**
+     * Returns the {@link SymbolLookup} to be used for the tree-sitter native library.
+     *
+     * @param arena an arena for the symbol lookup
+     * @return the {@link SymbolLookup} to be used for the tree-sitter native library
+     */
+    SymbolLookup get(Arena arena);
+}

src/main/java/io/github/treesitter/jtreesitter/internal/ChainedLibraryLookup.java

@@ -0,0 +1,29 @@
+package io.github.treesitter.jtreesitter.internal;
+
+import io.github.treesitter.jtreesitter.NativeLibraryLookup;
+import java.lang.foreign.Arena;
+import java.lang.foreign.Linker;
+import java.lang.foreign.SymbolLookup;
+import java.util.Optional;
+import java.util.ServiceLoader;
+
+final class ChainedLibraryLookup implements NativeLibraryLookup {
+    @Override
+    public SymbolLookup get(Arena arena) {
+        var serviceLoader = ServiceLoader.load(NativeLibraryLookup.class);
+        SymbolLookup lookup = (name) -> Optional.empty();
+        for (var libraryLookup : serviceLoader) {
+            lookup = lookup.or(libraryLookup.get(arena));
+        }
+        return lookup.or(findLibrary(arena)).or(Linker.nativeLinker().defaultLookup());
+    }
+
+    private SymbolLookup findLibrary(Arena arena) {
+        try {
+            String library = System.mapLibraryName("tree-sitter");
+            return SymbolLookup.libraryLookup(library, arena);
+        } catch (IllegalArgumentException e) {
+            return SymbolLookup.loaderLookup();
+        }
+    }
+}