Split libpkl libraries between shared and static libs (#1812)

This adds a `libpkl-static.pc` so pkg-config users can link either
statically or dynamically via `pkg-config --libs libpkl`, or
`pkg-config --libs libpkl-static`.

Additionally, this fixes an issue where the replace tokens wasn't
doing anything, leaving the `@version@` token intact in the archive.

Additionally, this adds an `-install_name` when building the dylib for macOS.

Co-authored-by: Islon Scherer <islonscherer@gmail.com>

docs/modules/libpkl/pages/index.adoc

@@ -1,4 +1,5 @@
 = libpkl
+include::ROOT:partial$component-attributes.adoc[]
 
 libpkl is a C library for driving Pkl evaluation.
 
@@ -32,9 +33,10 @@ The archive has the following structure:
     ├── include
     │   └── pkl.h
     ├── lib
+    │   ├── libpkl.<shared library extension>
     │   ├── libpkl.<static library extension>
-    │   ├── libpkl.<dynamic library extension>
     │   └── pkgconfig
+    │       ├── libpkl-static.pc
     │       └── libpkl.pc
     ├── LICENSE.txt
     ├── README.md
@@ -43,7 +45,7 @@ The archive has the following structure:
 
 The file extensions are as follows:
 |===
-|OS |Static Library Extension |Dynamic library extension
+|OS |Static Library Extension |Shared library extension
 
 |macOS
 |`.a`
@@ -58,6 +60,44 @@ The file extensions are as follows:
 |`.dll`
 |===
 
+=== Linking to the static vs. shared library
+
+The simplest way to configure your compiler to link to either the static or the shared library is to use https://en.wikipedia.org/wiki/Pkg-config[pkg-config].
+
+The libpkl library ships with two pkg-config files: `libpkl.pc`, and `libpkl-static.pc`.
+
+The normal `libpkl.pc` links to the shared library.
+
+To unambiguously link to the static library, use `libpkl-static.pc`.
+
+For example, when using `cc`:
+
+[source,shell]
+----
+# Link against the shared library
+cc -o myprogram myprogram.c $(pkg-config --libs --cflags libpkl)
+
+# Link against the static library
+cc -o myprogram myprogram.c $(pkg-config --static --libs --cflags libpkl-static)
+----
+
+
+If libpkl is installed in a non-system directory, set `PKG_CONFIG_PATH` to the subpath `lib/pkgconfig` within the directory that contains libpkl. For example, given libpkl directory `/path/to/libpkl`, the environment variable should have `/path/to/libpkl/lib/pkgconfig`.
+
+NOTE: Windows can use pkg-config through the https://www.msys2.org/docs/pkgconfig/[MSYS2 toolchain]. Using pkg-config on Windows implies compiling with gcc-style compiler like https://code.visualstudio.com/docs/cpp/config-mingw[MinGW], instead of MSVC.
+
+[NOTE]
+====
+It's also possible to link to the static library with the normal `libpkl.pc`.
+
+For example:
+
+[source,shell]
+----
+cc -Wl,-Bstatic $(pkg-config --libs --cflags libpkl)
+----
+====
+
 == Building libpkl from source
 
 To build libpkl from source, the apple/pkl repository first must be cloned down to a host OS.
@@ -79,7 +119,10 @@ cd pkl/
 ./gradlew libpkl:buildNative
 ----
 
-The resulting archive will be written to `libpkl/build/distributions`.
+This results in two directories of interest:
+
+* `libpkl/build/distributions/`: directory containing archives (`.zip` on Windows, `.tar.gz` on macOS/Linux) of C libraries.
+* `libpkl/build/native-libs/<os>-<arch>`: directory containing the built library files (the inner structure of the archive).
 
 Cross-compilation is not supported.
 

libpkl/libpkl.gradle.kts

@@ -251,16 +251,11 @@ val buildSharedLibrary =
       frameworks.addAll("Foundation", "CoreServices")
       linkerFlags.addAll("-current_version", project.version.toString())
       linkerFlags.addAll("-compatibility_version", "0.1.0")
-
-      // libpkl_internal_s bundles Native Image's own JNI-named implementations of JDK native
-      // methods (e.g. Java_sun_nio_ch_UnixFileDispatcherImpl_write0), which by default get
-      // exported with global visibility. Loading libpkl.dylib into a JVM process (e.g. via JNA)
-      // then lets the host JVM's own native-method resolution bind to these internal
-      // implementations instead of the JDK's real ones, silently corrupting unrelated file I/O.
-      // Restrict the dylib's exported symbols to just the public pkl_* API to prevent this.
+      // prevent JNI symbols from being exported and clobbering the symbol table
       val exportedSymbolsFile = file("src/main/c/pkl.exported_symbols")
       inputs.file(exportedSymbolsFile)
       linkerFlags.addAll("-exported_symbols_list", exportedSymbolsFile.absolutePath)
+      compilerArgs.addAll("-install_name", "@rpath/libpkl.dylib")
     }
 
     if (targetMachine.os.isWindows) {
@@ -276,9 +271,7 @@ val buildSharedLibrary =
 
     if (targetMachine.os.isLinux) {
       libraries.add("dl")
-
-      // Same symbol-collision hazard as the macOS case above (see comment there), but scoped via
-      // a GNU ld version script instead of an exported-symbols list.
+      // prevent JNI symbols from being exported and clobbering the symbol table
       val versionScriptFile = file("src/main/c/pkl.map")
       inputs.file(versionScriptFile)
       linkerFlags.add("--version-script=${versionScriptFile.absolutePath}")
@@ -317,7 +310,7 @@ val distZip =
     into(baseName)
   }
 
-tasks.assembleNative { dependsOn(distZip, distTar) }
+tasks.assembleNative { dependsOn(distZip, distTar, processFiles) }
 
 val processFiles =
   tasks.register<Copy>("processFiles") {
@@ -329,9 +322,23 @@ val processFiles =
     includeEmptyDirs = true
     into(buildInfo.targetMachine.outputDir)
 
-    filesMatching("libpkl.pc") {
-      filter<ReplaceTokens>("tokens" to mapOf("version" to buildInfo.pklVersion))
+    val tokens = buildMap {
+      this["version"] = buildInfo.pklVersion
+      this["static_lib_filename"] = "libpkl.${buildInfo.os.staticLibraryExtension}"
+      this["extra_static_libs"] =
+        when {
+          buildInfo.os.isMacOS -> " -lz -framework Foundation -framework CoreServices"
+          buildInfo.os.isWindows -> ""
+          else -> " -lz"
+        }
+      this["extra_shared_libs"] =
+        when {
+          buildInfo.os.isMacOS -> " -lpkl"
+          buildInfo.os.isWindows -> " -l:libpkl_dll.lib"
+          else -> " -lpkl"
+        }
     }
+    filesMatching("**/libpkl*.pc") { filter<ReplaceTokens>("tokens" to tokens) }
   }
 
 val testNativeJava =
@@ -428,8 +435,6 @@ val compileNativeTestDynamic =
       libraryFiles.from(buildInfo.targetMachine.libraryDir.map { it.file("libpkl_dll.lib") })
     } else {
       libraries.add("pkl")
-      libraries.add("z")
-      libraries.add("pthread")
       // Bake the library's location into the test executable so the dynamic loader can find
       // libpkl.so/libpkl.dylib without needing LD_LIBRARY_PATH/DYLD_LIBRARY_PATH set at run time.
       linkerFlags.add("-rpath")

libpkl/src/main/files/lib/pkgconfig/libpkl-static.pc

@@ -0,0 +1,11 @@
+prefix=${pcfiledir}/../..
+exec_prefix=${prefix}
+libdir=${exec_prefix}/lib
+includedir=${prefix}/include
+
+Name: libpkl
+Description: C library for calling into Pkl's message passing API.
+URL: https://pkl-lang.org/main/current/libpkl/index.html
+Version: @version@
+Libs: ${libdir}/@static_lib_filename@@extra_static_libs@
+Cflags: -I${includedir}

libpkl/src/main/files/lib/pkgconfig/libpkl.pc

@@ -7,5 +7,5 @@ Name: libpkl
 Description: C library for calling into Pkl's message passing API.
 URL: https://pkl-lang.org/main/current/libpkl/index.html
 Version: @version@
-Libs: -L${libdir} -lpkl -lz -lpthread
+Libs: -L${libdir}@extra_shared_libs@
 Cflags: -I${includedir}