From c060d314930c5552b99a89278a6a695baf0352da Mon Sep 17 00:00:00 2001
From: Uzair Aftab <git@uzaaft.me>
Date: Thu, 20 Aug 2026 21:44:55 +0200
Subject: [PATCH] build: avoid duplicate C API compilation

---
 README.md       |  4 ++++
 build.zig       | 48 ++++++++++++++++++++++++++++++++++++++++++------
 include/vaxis.h |  3 ++-
 3 files changed, 48 insertions(+), 7 deletions(-)

diff --git a/README.md b/README.md
index 225492f..a58d989 100644
--- a/README.md
+++ b/README.md
@@ -446,6 +446,10 @@ This installs `libvaxis.a`, `libvaxis.so`, and the `vaxis.h` header into
 [include/vaxis.h](include/vaxis.h); a complete example lives at
 [examples/c/parse.c](examples/c/parse.c).
 
+When only one linkage is needed, use `zig build lib-static` or
+`zig build lib-shared`. The combined `lib` step compiles the C API once and
+reuses that object code for both library formats.
+
 Events are opaque handles read through accessor functions, so event
 payloads can grow without breaking the ABI. Event data is owned by the
 parser and valid until the next parse call; nothing is freed by the caller.
diff --git a/build.zig b/build.zig
index 2e687dd..034b2be 100644
--- a/build.zig
+++ b/build.zig
@@ -60,6 +60,7 @@ pub fn build(b: *std.Build) void {
         .root_source_file = b.path("src/c_api.zig"),
         .target = target,
         .optimize = optimize,
+        .pic = true,
         .link_libc = true,
         .imports = &.{
             .{ .name = "vaxis", .module = vaxis_mod },
@@ -69,24 +70,59 @@ pub fn build(b: *std.Build) void {
     // For the @cImport-based layout test in src/c_api.zig
     c_api_mod.addIncludePath(b.path("include"));
 
-    const lib_step = b.step("lib", "Build the C library (static and shared)");
+    // Compile the C API once as PIC, then use the resulting object for both
+    // library formats. Building two libraries directly from c_api_mod would
+    // run Zig's frontend and code generator once per linkage.
+    const c_api_object = b.addObject(.{
+        .name = "vaxis-c-api",
+        .root_module = c_api_mod,
+        .use_llvm = use_llvm,
+    });
+
+    const static_mod = b.createModule(.{
+        .target = target,
+        .optimize = optimize,
+        .link_libc = true,
+    });
+    static_mod.addObject(c_api_object);
     const static_lib = b.addLibrary(.{
         // the DLL import library is also named vaxis.lib on Windows
         .name = if (target.result.os.tag == .windows) "vaxis-static" else "vaxis",
         .linkage = .static,
-        .root_module = c_api_mod,
+        .root_module = static_mod,
         .use_llvm = use_llvm,
     });
-    static_lib.installHeadersDirectory(b.path("include"), "", .{});
+
+    const shared_mod = b.createModule(.{
+        .target = target,
+        .optimize = optimize,
+        .link_libc = true,
+    });
+    shared_mod.addObject(c_api_object);
     const shared_lib = b.addLibrary(.{
         .name = "vaxis",
         .linkage = .dynamic,
-        .root_module = c_api_mod,
+        .root_module = shared_mod,
         .use_llvm = use_llvm,
         .version = std.SemanticVersion.parse(version_string) catch unreachable,
     });
-    lib_step.dependOn(&b.addInstallArtifact(static_lib, .{}).step);
-    lib_step.dependOn(&b.addInstallArtifact(shared_lib, .{}).step);
+
+    const install_static = b.addInstallArtifact(static_lib, .{});
+    const install_shared = b.addInstallArtifact(shared_lib, .{});
+    const install_headers = b.addInstallDirectory(.{
+        .source_dir = b.path("include"),
+        .install_dir = .header,
+        .install_subdir = "",
+    });
+    const lib_static_step = b.step("lib-static", "Build the static C library");
+    lib_static_step.dependOn(&install_static.step);
+    lib_static_step.dependOn(&install_headers.step);
+    const lib_shared_step = b.step("lib-shared", "Build the shared C library");
+    lib_shared_step.dependOn(&install_shared.step);
+    lib_shared_step.dependOn(&install_headers.step);
+    const lib_step = b.step("lib", "Build the C library (static and shared)");
+    lib_step.dependOn(lib_static_step);
+    lib_step.dependOn(lib_shared_step);
 
     // Examples
     const Example = enum {
diff --git a/include/vaxis.h b/include/vaxis.h
index 4b54304..3315045 100644
--- a/include/vaxis.h
+++ b/include/vaxis.h
@@ -10,7 +10,8 @@
  * parser; the caller never frees anything. Copy what you need longer.
  *
  * Build with `zig build lib`, which produces libvaxis.a / libvaxis.so and
- * installs this header.
+ * installs this header. Use `zig build lib-static` or `zig build lib-shared`
+ * when only one linkage is needed.
  */
 
 #ifndef VAXIS_H
-- 
2.51.2