feat(language): add static load function

Closes #23

Author: ObserverOfTime

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

@@ -1,10 +1,10 @@
 package io.github.treesitter.jtreesitter;
 
+import java.lang.foreign.*;
 import static io.github.treesitter.jtreesitter.internal.TreeSitter.*;
 
 import io.github.treesitter.jtreesitter.internal.TreeSitter;
-import java.lang.foreign.Arena;
-import java.lang.foreign.MemorySegment;
+
 import org.jspecify.annotations.NullMarked;
 import org.jspecify.annotations.Nullable;
 
@@ -22,6 +22,13 @@ public final class Language {
     /** The earliest ABI version that is supported by the current version of the library. */
     public static final @Unsigned int MIN_COMPATIBLE_LANGUAGE_VERSION = TREE_SITTER_MIN_COMPATIBLE_LANGUAGE_VERSION();
 
+    private static final ValueLayout VOID_PTR =
+        ValueLayout.ADDRESS.withTargetLayout(MemoryLayout.sequenceLayout(Long.MAX_VALUE, ValueLayout.JAVA_BYTE));
+
+    private static final FunctionDescriptor FUNC_DESC = FunctionDescriptor.of(VOID_PTR);
+
+    private static final Linker LINKER = Linker.nativeLinker();
+
     private final MemorySegment self;
 
     private final @Unsigned int version;
@@ -43,6 +50,37 @@ public Language(MemorySegment self) throws IllegalArgumentException {
         }
     }
 
+    private static UnsatisfiedLinkError unresolved(String name) {
+        return new UnsatisfiedLinkError("Unresolved symbol: %s".formatted(name));
+    }
+
+    /**
+     * Load a language by looking for its function in the given symbols.
+     *
+     * <h4 id="load-example">Example</h4>
+     *
+     * <p>{@snippet lang="java" :
+     * Language language;
+     * try (Arena arena = Arena.ofConfined()) {
+     *    String library = System.mapLibraryName("tree-sitter-java");
+     *    SymbolLookup symbols = SymbolLookup.libraryLookup(library, arena);
+     *    language = Language.load(symbols, "tree_sitter_java");
+     * }
+     * }
+     *
+     * @throws RuntimeException If the language could not be loaded.
+     */
+    // TODO: deprecate when the bindings are generated by the CLI
+    public static Language load(SymbolLookup symbols, String language) throws RuntimeException {
+        var address = symbols.find(language).orElseThrow(() -> unresolved(language));
+        try {
+            var function = LINKER.downcallHandle(address, FUNC_DESC);
+            return new Language((MemorySegment) function.invokeExact());
+        } catch (Throwable e) {
+            throw new RuntimeException("Failed to load %s".formatted(language), e);
+        }
+    }
+
     MemorySegment segment() {
         return self;
     }