test/link: add test for extern resolution

Adds a linker tests to verify extern/undefined symbols
representing non-functions are being resolved correctly.

src/arch/wasm/CodeGen.zig

@@ -2355,7 +2355,7 @@ fn lowerDeclRefValue(self: *Self, tv: TypedValue, decl_index: Module.Decl.Index)
 
     const module = self.bin_file.base.options.module.?;
     const decl = module.declPtr(decl_index);
-    if (!decl.ty.hasRuntimeBitsIgnoreComptime()) {
+    if (decl.ty.zigTypeTag() != .Fn and !decl.ty.hasRuntimeBitsIgnoreComptime()) {
         return WValue{ .imm32 = 0xaaaaaaaa };
     }
 

test/link.zig

@@ -52,6 +52,12 @@ fn addWasmCases(cases: *tests.StandaloneContext) void {
         .build_modes = true,
         .requires_stage2 = true,
     });
+
+    cases.addBuildFile("test/link/wasm/extern/build.zig", .{
+        .build_modes = true,
+        .requires_stage2 = true,
+        .use_emulation = true,
+    });
 }
 
 fn addMachOCases(cases: *tests.StandaloneContext) void {

test/link/wasm/extern/build.zig

@@ -0,0 +1,17 @@
+const std = @import("std");
+
+pub fn build(b: *std.build.Builder) void {
+    const mode = b.standardReleaseOptions();
+    const exe = b.addExecutable("extern", "main.zig");
+    exe.setTarget(.{ .cpu_arch = .wasm32, .os_tag = .wasi });
+    exe.setBuildMode(mode);
+    exe.addCSourceFile("foo.c", &.{});
+    exe.use_llvm = false;
+    exe.use_lld = false;
+
+    const run = exe.runEmulatable();
+    run.expectStdOutEqual("Result: 30");
+
+    const test_step = b.step("test", "Run linker test");
+    test_step.dependOn(&run.step);
+}

test/link/wasm/extern/foo.c

@@ -0,0 +1 @@
+int foo = 30;

test/link/wasm/extern/main.zig

@@ -0,0 +1,8 @@
+const std = @import("std");
+
+extern const foo: u32;
+
+pub fn main() void {
+    const std_out = std.io.getStdOut();
+    std_out.writer().print("Result: {d}", .{foo}) catch {};
+}