From 29717fefb8e951561bd51fdcea54ec62af3fd7dd Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Wed, 14 Oct 2026 15:30:56 -0700
Subject: [PATCH] start code: flatten and improve missing pub fn main message

better error message when the programmer omits `main` or fails to make
it public.

closes #37113
---
 lib/std/start.zig | 76 +++++++++++++++++++++++++----------------------
 1 file changed, 41 insertions(+), 35 deletions(-)

diff --git a/lib/std/start.zig b/lib/std/start.zig
index d77c093d23792f1422d4cfdc2e8d97a2af181b7d..2ed247f591505f8dc4db264e6f6018f0f5bab1b1 100644
--- a/lib/std/start.zig
+++ b/lib/std/start.zig
@@ -29,49 +29,54 @@ comptime {
             }
         }
     } else if (builtin.output_mode == .Exe or @hasDecl(root, "main")) {
-        if (builtin.link_libc and @hasDecl(root, "main")) {
+        if (builtin.link_libc and (@hasDecl(root, "main") or std.os.requiresLibC())) {
             if (is_wasm) {
                 @export(&mainWithoutEnv, .{ .name = "__main_argc_argv" });
             } else if (!@typeInfo(@TypeOf(root.main)).@"fn".attrs.@"callconv".eql(.c)) {
                 @export(&main, .{ .name = "main" });
             }
-        } else if (native_os == .windows and builtin.link_libc and @hasDecl(root, "wWinMain")) {
-            if (!@typeInfo(@TypeOf(root.wWinMain)).@"fn".attrs.@"callconv".eql(.c)) {
-                @export(&wWinMain, .{ .name = "wWinMain" });
-            }
-        } else if (native_os == .windows) {
-            if (!@hasDecl(root, "WinMain") and !@hasDecl(root, "WinMainCRTStartup") and
-                !@hasDecl(root, "wWinMain") and !@hasDecl(root, "wWinMainCRTStartup"))
-            {
-                @export(&WinStartup, .{ .name = "wWinMainCRTStartup" });
-            } else if (@hasDecl(root, "WinMain") and !@hasDecl(root, "WinMainCRTStartup") and
-                !@hasDecl(root, "wWinMain") and !@hasDecl(root, "wWinMainCRTStartup"))
-            {
-                @compileError("WinMain not supported; declare wWinMain or main instead");
-            } else if (@hasDecl(root, "wWinMain") and !@hasDecl(root, "wWinMainCRTStartup") and
-                !@hasDecl(root, "WinMain") and !@hasDecl(root, "WinMainCRTStartup"))
-            {
-                @export(&wWinMainCRTStartup, .{ .name = "wWinMainCRTStartup" });
-            }
-        } else if (native_os == .uefi) {
-            if (!@hasDecl(root, "EfiMain")) @export(&EfiMain, .{ .name = "EfiMain" });
-        } else if (native_os == .wasi) {
-            const wasm_start_sym = switch (builtin.wasi_exec_model) {
-                .reactor => "_initialize",
-                .command => "_start",
-            };
-            if (!@hasDecl(root, wasm_start_sym) and @hasDecl(root, "main")) {
+        } else switch (native_os) {
+            .windows => {
+                if (builtin.link_libc and @hasDecl(root, "wWinMain")) {
+                    if (!@typeInfo(@TypeOf(root.wWinMain)).@"fn".attrs.@"callconv".eql(.c)) {
+                        @export(&wWinMain, .{ .name = "wWinMain" });
+                    }
+                } else if (!@hasDecl(root, "WinMain") and !@hasDecl(root, "WinMainCRTStartup") and
+                    !@hasDecl(root, "wWinMain") and !@hasDecl(root, "wWinMainCRTStartup"))
+                {
+                    @export(&WinStartup, .{ .name = "wWinMainCRTStartup" });
+                } else if (@hasDecl(root, "WinMain") and !@hasDecl(root, "WinMainCRTStartup") and
+                    !@hasDecl(root, "wWinMain") and !@hasDecl(root, "wWinMainCRTStartup"))
+                {
+                    @compileError("WinMain not supported; declare wWinMain or main instead");
+                } else if (@hasDecl(root, "wWinMain") and !@hasDecl(root, "wWinMainCRTStartup") and
+                    !@hasDecl(root, "WinMain") and !@hasDecl(root, "WinMainCRTStartup"))
+                {
+                    @export(&wWinMainCRTStartup, .{ .name = "wWinMainCRTStartup" });
+                }
+            },
+
+            .uefi => {
+                if (!@hasDecl(root, "EfiMain")) @export(&EfiMain, .{ .name = "EfiMain" });
+            },
+            .wasi => {
+                const wasm_start_sym = switch (builtin.wasi_exec_model) {
+                    .reactor => "_initialize",
+                    .command => "_start",
+                };
+                if (!@hasDecl(root, wasm_start_sym) and @hasDecl(root, "main")) {
+                    // Only call main when defined. For WebAssembly it's allowed to pass `-fno-entry` in which
+                    // case it's not required to provide an entrypoint such as main.
+                    @export(&startWasi, .{ .name = wasm_start_sym });
+                }
+            },
+            .freestanding => if (is_wasm) {
                 // Only call main when defined. For WebAssembly it's allowed to pass `-fno-entry` in which
                 // case it's not required to provide an entrypoint such as main.
-                @export(&startWasi, .{ .name = wasm_start_sym });
-            }
-        } else if (is_wasm and native_os == .freestanding) {
-            // Only call main when defined. For WebAssembly it's allowed to pass `-fno-entry` in which
-            // case it's not required to provide an entrypoint such as main.
-            if (!@hasDecl(root, start_sym_name) and @hasDecl(root, "main")) @export(&wasm_freestanding_start, .{ .name = start_sym_name });
-        } else switch (native_os) {
+                if (!@hasDecl(root, start_sym_name) and @hasDecl(root, "main"))
+                    @export(&wasm_freestanding_start, .{ .name = start_sym_name });
+            },
             .other,
-            .freestanding,
             .vulkan,
             .opengl,
             .opencl,
@@ -85,6 +90,7 @@ comptime {
             .psp,
             .vita,
             => {},
+
             else => if (!@hasDecl(root, start_sym_name)) @export(&_start, .{ .name = start_sym_name }),
         }
     }
-- 
2.54.0