Allow defining zopengl export-linkage at build time (#33)

Author: pascalPost

build.zig

@@ -7,9 +7,18 @@ pub fn build(b: *std.Build) void {
         .preferred_optimize_mode = .ReleaseSafe,
     });
 
-    _ = b.addModule("root", .{
+    const default_export_linkage: std.builtin.GlobalLinkage =
+        if (target.result.os.tag == .emscripten) .weak else .strong;
+    const export_linkage = b.option(std.builtin.GlobalLinkage, "export_linkage", "Global linkage for exported OpenGL C symbols") orelse
+        default_export_linkage;
+
+    const build_options = b.addOptions();
+    build_options.addOption(std.meta.Tag(std.builtin.GlobalLinkage), "linkage", @intFromEnum(export_linkage));
+
+    const root = b.addModule("root", .{
         .root_source_file = b.path("src/zopengl.zig"),
     });
+    root.addOptions("build_options", build_options);
 
     {
         const test_step = b.step("test", "Run zopengl tests");
@@ -22,6 +31,7 @@ pub fn build(b: *std.Build) void {
                 .optimize = optimize,
             }),
         });
+        tests.root_module.addOptions("build_options", build_options);
         b.installArtifact(tests);
 
         test_step.dependOn(&b.addRunArtifact(tests).step);
@@ -36,5 +46,6 @@ pub fn build(b: *std.Build) void {
             .optimize = optimize,
         }),
     });
+    lib.root_module.addOptions("build_options", build_options);
     _ = b.installArtifact(lib);
 }

src/zopengl.zig

@@ -2,6 +2,7 @@ const std = @import("std");
 const assert = std.debug.assert;
 
 const options = @import("zopengl_options");
+const build_options = @import("build_options");
 
 comptime {
     @setEvalBranchQuota(20_000);
@@ -1371,7 +1372,7 @@ fn getProcAddress(comptime T: type, proc_name: [:0]const u8) !T {
 // C exports
 //
 //--------------------------------------------------------------------------------------------------
-const linkage: @import("std").builtin.GlobalLinkage = .strong;
+const linkage: std.builtin.GlobalLinkage = @enumFromInt(build_options.linkage);
 comptime {
     //----------------------------------------------------------------------------------------------
     // OpenGL 1.0 (Core Profile)