self hosted zig: print usage

build.zig

@@ -2,6 +2,16 @@ const Builder = @import("std").build.Builder;
 const tests = @import("test/tests.zig");
 
 pub fn build(b: &Builder) {
+    const mode = b.standardReleaseOptions();
+
+    var exe = b.addExecutable("zig", "src-self-hosted/main.zig");
+    exe.setBuildMode(mode);
+    exe.linkSystemLibrary("c");
+    b.default_step.dependOn(&exe.step);
+
+    b.installArtifact(exe);
+
+
     const test_filter = b.option([]const u8, "test-filter", "Skip tests that do not match filter");
     const with_lldb = b.option(bool, "with-lldb", "Run tests in LLDB to get a backtrace if one fails") ?? false;
     const test_step = b.step("test", "Run all the tests");

src-self-hosted/main.zig

@@ -0,0 +1,112 @@
+const io = @import("std").io;
+const os = @import("std").os;
+const heap = @import("std").mem;
+
+// TODO: OutSteam and InStream interface
+// TODO: move allocator to heap namespace
+
+error InvalidArgument;
+error MissingArg0;
+
+pub fn main() -> %void {
+    if (internal_main()) |_| {
+        return;
+    } else |err| {
+        if (err == error.InvalidArgument) {
+            io.stderr.printf("\n") %% return err;
+            printUsage(&io.stderr) %% return err;
+        } else {
+            io.stderr.printf("{}\n", err) %% return err;
+        }
+        return err;
+    }
+}
+
+pub fn internal_main() -> %void {
+    var args_it = os.args();
+
+    var incrementing_allocator = heap.IncrementingAllocator.init(10 * 1024 * 1024) %% |err| {
+        io.stderr.printf("Unable to allocate memory") %% {};
+        return err;
+    };
+    defer incrementing_allocator.deinit();
+
+    const allocator = &incrementing_allocator.allocator;
+
+    const arg0 = %return (args_it.next(allocator) ?? error.MissingArg0);
+    defer allocator.free(arg0);
+
+    %return printUsage(&io.stdout);
+}
+
+fn printUsage(outstream: &io.OutStream) -> %void {
+    %return outstream.write(
+        \\Usage: zig [command] [options]
+        \\Commands:
+        \\  build                        build project from build.zig
+        \\  build-exe [source]           create executable from source or object files
+        \\  build-lib [source]           create library from source or object files
+        \\  build-obj [source]           create object from source or assembly
+        \\  parsec [source]              convert c code to zig code
+        \\  targets                      list available compilation targets
+        \\  test [source]                create and run a test build
+        \\  version                      print version number and exit
+        \\  zen                          print zen of zig and exit
+        \\Compile Options:
+        \\  --assembly [source]          add assembly file to build
+        \\  --cache-dir [path]           override the cache directory
+        \\  --color [auto|off|on]        enable or disable colored error messages
+        \\  --enable-timing-info         print timing diagnostics
+        \\  --libc-include-dir [path]    directory where libc stdlib.h resides
+        \\  --name [name]                override output name
+        \\  --output [file]              override destination path
+        \\  --output-h [file]            override generated header file path
+        \\  --pkg-begin [name] [path]    make package available to import and push current pkg
+        \\  --pkg-end                    pop current pkg
+        \\  --release-fast               build with optimizations on and safety off
+        \\  --release-safe               build with optimizations on and safety on
+        \\  --static                     output will be statically linked
+        \\  --strip                      exclude debug symbols
+        \\  --target-arch [name]         specify target architecture
+        \\  --target-environ [name]      specify target environment
+        \\  --target-os [name]           specify target operating system
+        \\  --verbose                    turn on compiler debug output
+        \\  --verbose-link               turn on compiler debug output for linking only
+        \\  --verbose-ir                 turn on compiler debug output for IR only
+        \\  --zig-install-prefix [path]  override directory where zig thinks it is installed
+        \\  -dirafter [dir]              same as -isystem but do it last
+        \\  -isystem [dir]               add additional search path for other .h files
+        \\  -mllvm [arg]                 additional arguments to forward to LLVM's option processing
+        \\Link Options:
+        \\  --ar-path [path]             set the path to ar
+        \\  --dynamic-linker [path]      set the path to ld.so
+        \\  --each-lib-rpath             add rpath for each used dynamic library
+        \\  --libc-lib-dir [path]        directory where libc crt1.o resides
+        \\  --libc-static-lib-dir [path] directory where libc crtbegin.o resides
+        \\  --msvc-lib-dir [path]        (windows) directory where vcruntime.lib resides
+        \\  --kernel32-lib-dir [path]    (windows) directory where kernel32.lib resides
+        \\  --library [lib]              link against lib
+        \\  --library-path [dir]         add a directory to the library search path
+        \\  --linker-script [path]       use a custom linker script
+        \\  --object [obj]               add object file to build
+        \\  -L[dir]                      alias for --library-path
+        \\  -rdynamic                    add all symbols to the dynamic symbol table
+        \\  -rpath [path]                add directory to the runtime library search path
+        \\  -mconsole                    (windows) --subsystem console to the linker
+        \\  -mwindows                    (windows) --subsystem windows to the linker
+        \\  -municode                    (windows) link with unicode
+        \\  -framework [name]            (darwin) link against framework
+        \\  -mios-version-min [ver]      (darwin) set iOS deployment target
+        \\  -mmacosx-version-min [ver]   (darwin) set Mac OS X deployment target
+        \\  --ver-major [ver]            dynamic library semver major version
+        \\  --ver-minor [ver]            dynamic library semver minor version
+        \\  --ver-patch [ver]            dynamic library semver patch version
+        \\Test Options:
+        \\  --test-filter [text]         skip tests that do not match filter
+        \\  --test-name-prefix [text]    add prefix to all tests
+        \\  --test-cmd [arg]             specify test execution command one arg at a time
+        \\  --test-cmd-bin               appends test binary path to test cmd args
+        \\
+    );
+    %return outstream.flush();
+}