Confusing error when build.zig file does not contain a "build" function

[zxubian]

Zig Version

0.9.1 (windows, chocolatey)

Steps to Reproduce

1. Create a "hello-world" project with the following build.zig file:

const Builder = @import("std").build.Builder;
// note that Build starts with a capital 'B'
pub fn Build(b: *Builder) void {
    const target = b.standardTargetOptions(.{});
    const mode = b.standardReleaseOptions();
    const exe = b.addExecutable("init-exe", "src/main.zig");
    exe.setTarget(target);
    exe.setBuildMode(mode);
    exe.install();
    const run_cmd = exe.run();
    run_cmd.step.dependOn(b.getInstallStep());
    const run_step = b.step("run", "Run the app");
    run_step.dependOn(&run_cmd.step);
}

2. run zig build from the command line

Expected Behavior

A helpful error is displayed, notifying the user that they should have a function called "build" in their build.zig file, and that such a function could not be found.

Actual Behavior

The following error is displayed:

C:\ProgramData\chocolatey\lib\zig\tools\zig-windows-x86_64-0.9.1\lib\std\special\build_runner.zig:219:45: error: container '.@build' has no member called 'build'
    switch (@typeInfo(@typeInfo(@TypeOf(root.build)).Fn.return_type.?)) {

This error message mentions a ".@build container", which is not helpful for new users, who do not know the internals of the build system.
The message can be improved by guiding the user to check that they have indeed correctly defined the 'build' function.
E.g.:

Could not find a function definition for 'build' in build.zig

[Vexu]

Same applies to missing main when using build-exe and run:

zig/lib/std/start.zig:561:45: error: struct 'a.a' has no member named 'main'
    switch (@typeInfo(@typeInfo(@TypeOf(root.main)).Fn.return_type.?)) {
                                        ~~~~^~~~~
a.zig:1:1: note: struct declared here

^
zig/lib/std/start.zig:510:12: note: called from here
    return @call(.{ .modifier = .always_inline }, callMain, .{});
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
zig/lib/std/start.zig:460:36: note: called from here
    return initEventLoopAndCallMain();
           ~~~~~~~~~~~~~~~~~~~~~~~~^~
zig/lib/std/start.zig:424:17: note: called from here
    std.os.exit(@call(.{ .modifier = .always_inline }, callMainWithArgs, .{ argc, argv, envp }));
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
zig/lib/std/start.zig:561:45: error: struct 'a.a' has no member named 'main'
    switch (@typeInfo(@typeInfo(@TypeOf(root.main)).Fn.return_type.?)) {
                                        ~~~~^~~~~
a.zig:1:1: note: struct declared here

^
zig/lib/std/start.zig:510:12: note: called from here
    return @call(.{ .modifier = .always_inline }, callMain, .{});
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
zig/lib/std/start.zig:460:36: note: called from here
    return initEventLoopAndCallMain();
           ~~~~~~~~~~~~~~~~~~~~~~~~^~
zig/lib/std/start.zig:561:45: error: struct 'a.a' has no member named 'main'
    switch (@typeInfo(@typeInfo(@TypeOf(root.main)).Fn.return_type.?)) {
                                        ~~~~^~~~~
a.zig:1:1: note: struct declared here

^