std.Build: implement --host-target, --host-cpu, --host-dynamic-linker

This also makes a long-overdue change of extracting common state from
Build into a shared Graph object.

Getting the semantics right for these flags turned out to be quite
tricky. In the end it works like this:
* The override only happens when the target is fully native, with no
  additional query parameters, such as versions or CPU features added.
* The override affects the resolved Target but leaves the original Query
  unmodified.
* The "is native?" detection logic operates on the original, unmodified
  query. This makes it possible to provide invalid host target
  information, causing confusing errors to occur. Don't do that.

There are some minor breaking changes to std.Build API such as the fact
that `b.zig_exe` is now moved to `b.graph.zig_exe`, as well as a handful
of other similar flags.

8 files changed, 42 insertions, 31 deletions

diff --git a/lib/std/Build/Step/Compile.zig b/lib/std/Build/Step/Compile.zig
index 68e68b28ad..0c438069f8 100644
--- a/lib/std/Build/Step/Compile.zig
+++ b/lib/std/Build/Step/Compile.zig
@@ -923,7 +923,7 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
     var zig_args = ArrayList([]const u8).init(arena);
     defer zig_args.deinit();
 
-    try zig_args.append(b.zig_exe);
+    try zig_args.append(b.graph.zig_exe);
 
     const cmd = switch (self.kind) {
         .lib => "build-lib",
@@ -933,6 +933,16 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
     };
     try zig_args.append(cmd);
 
+    if (!mem.eql(u8, b.graph.host_query_options.arch_os_abi, "native")) {
+        try zig_args.appendSlice(&.{ "--host-target", b.graph.host_query_options.arch_os_abi });
+    }
+    if (b.graph.host_query_options.cpu_features) |cpu| {
+        try zig_args.appendSlice(&.{ "--host-cpu", cpu });
+    }
+    if (b.graph.host_query_options.dynamic_linker) |dl| {
+        try zig_args.appendSlice(&.{ "--host-dynamic-linker", dl });
+    }
+
     if (b.reference_trace) |some| {
         try zig_args.append(try std.fmt.allocPrint(arena, "-freference-trace={d}", .{some}));
     }
@@ -1393,7 +1403,7 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
     try zig_args.append(b.cache_root.path orelse ".");
 
     try zig_args.append("--global-cache-dir");
-    try zig_args.append(b.global_cache_root.path orelse ".");
+    try zig_args.append(b.graph.global_cache_root.path orelse ".");
 
     try zig_args.append("--name");
     try zig_args.append(self.name);
diff --git a/lib/std/Build/Step/ConfigHeader.zig b/lib/std/Build/Step/ConfigHeader.zig
index 55c7cf387a..9c2f5d0826 100644
--- a/lib/std/Build/Step/ConfigHeader.zig
+++ b/lib/std/Build/Step/ConfigHeader.zig
@@ -171,7 +171,7 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
     const gpa = b.allocator;
     const arena = b.allocator;
 
-    var man = b.cache.obtain();
+    var man = b.graph.cache.obtain();
     defer man.deinit();
 
     // Random bytes to make ConfigHeader unique. Refresh this with new
diff --git a/lib/std/Build/Step/Fmt.zig b/lib/std/Build/Step/Fmt.zig
index 8e8cc51c0d..b9828e34dd 100644
--- a/lib/std/Build/Step/Fmt.zig
+++ b/lib/std/Build/Step/Fmt.zig
@@ -52,7 +52,7 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
     var argv: std.ArrayListUnmanaged([]const u8) = .{};
     try argv.ensureUnusedCapacity(arena, 2 + 1 + self.paths.len + 2 * self.exclude_paths.len);
 
-    argv.appendAssumeCapacity(b.zig_exe);
+    argv.appendAssumeCapacity(b.graph.zig_exe);
     argv.appendAssumeCapacity("fmt");
 
     if (self.check) {
diff --git a/lib/std/Build/Step/ObjCopy.zig b/lib/std/Build/Step/ObjCopy.zig
index 6691107bf5..e10c5ce9a9 100644
--- a/lib/std/Build/Step/ObjCopy.zig
+++ b/lib/std/Build/Step/ObjCopy.zig
@@ -94,7 +94,7 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
     const b = step.owner;
     const self = @fieldParentPtr(ObjCopy, "step", step);
 
-    var man = b.cache.obtain();
+    var man = b.graph.cache.obtain();
     defer man.deinit();
 
     // Random bytes to make ObjCopy unique. Refresh this with new random
@@ -133,7 +133,7 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
     };
 
     var argv = std.ArrayList([]const u8).init(b.allocator);
-    try argv.appendSlice(&.{ b.zig_exe, "objcopy" });
+    try argv.appendSlice(&.{ b.graph.zig_exe, "objcopy" });
 
     if (self.only_section) |only_section| {
         try argv.appendSlice(&.{ "-j", only_section });
diff --git a/lib/std/Build/Step/Options.zig b/lib/std/Build/Step/Options.zig
index beaaf4e3a0..8dfe735703 100644
--- a/lib/std/Build/Step/Options.zig
+++ b/lib/std/Build/Step/Options.zig
@@ -222,7 +222,7 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
     const basename = "options.zig";
 
     // Hash contents to file name.
-    var hash = b.cache.hash;
+    var hash = b.graph.cache.hash;
     // Random bytes to make unique. Refresh this with new random bytes when
     // implementation is modified in a non-backwards-compatible way.
     hash.add(@as(u32, 0xad95e922));
@@ -301,27 +301,28 @@ test Options {
     var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
     defer arena.deinit();
 
-    const host: std.Build.ResolvedTarget = .{
-        .query = .{},
-        .result = try std.zig.system.resolveTargetQuery(.{}),
-    };
-
-    var cache: std.Build.Cache = .{
-        .gpa = arena.allocator(),
-        .manifest_dir = std.fs.cwd(),
+    var graph: std.Build.Graph = .{
+        .arena = arena.allocator(),
+        .cache = .{
+            .gpa = arena.allocator(),
+            .manifest_dir = std.fs.cwd(),
+        },
+        .zig_exe = "test",
+        .env_map = std.process.EnvMap.init(arena.allocator()),
+        .global_cache_root = .{ .path = "test", .handle = std.fs.cwd() },
     };
 
     var builder = try std.Build.create(
-        arena.allocator(),
-        "test",
+        &graph,
         .{ .path = "test", .handle = std.fs.cwd() },
         .{ .path = "test", .handle = std.fs.cwd() },
-        .{ .path = "test", .handle = std.fs.cwd() },
-        host,
-        &cache,
         &.{},
     );
-    defer builder.destroy();
+
+    builder.host = .{
+        .query = .{},
+        .result = try std.zig.system.resolveTargetQuery(.{}),
+    };
 
     const options = builder.addOptions();
 
diff --git a/lib/std/Build/Step/Run.zig b/lib/std/Build/Step/Run.zig
index de8f9816ab..2d49c48401 100644
--- a/lib/std/Build/Step/Run.zig
+++ b/lib/std/Build/Step/Run.zig
@@ -463,7 +463,7 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
     var argv_list = ArrayList([]const u8).init(arena);
     var output_placeholders = ArrayList(IndexedOutput).init(arena);
 
-    var man = b.cache.obtain();
+    var man = b.graph.cache.obtain();
     defer man.deinit();
 
     for (self.argv.items) |arg| {
@@ -747,7 +747,7 @@ fn runCommand(
                 exe.is_linking_libc;
             const other_target = exe.root_module.resolved_target.?.result;
             switch (std.zig.system.getExternalExecutor(b.host.result, &other_target, .{
-                .qemu_fixes_dl = need_cross_glibc and b.glibc_runtimes_dir != null,
+                .qemu_fixes_dl = need_cross_glibc and b.graph.glibc_runtimes_dir != null,
                 .link_libc = exe.is_linking_libc,
             })) {
                 .native, .rosetta => {
@@ -755,7 +755,7 @@ fn runCommand(
                     break :interpret;
                 },
                 .wine => |bin_name| {
-                    if (b.enable_wine) {
+                    if (b.graph.enable_wine) {
                         try interp_argv.append(bin_name);
                         try interp_argv.appendSlice(argv);
                     } else {
@@ -763,9 +763,9 @@ fn runCommand(
                     }
                 },
                 .qemu => |bin_name| {
-                    if (b.enable_qemu) {
+                    if (b.graph.enable_qemu) {
                         const glibc_dir_arg = if (need_cross_glibc)
-                            b.glibc_runtimes_dir orelse
+                            b.graph.glibc_runtimes_dir orelse
                                 return failForeign(self, "--glibc-runtimes", argv[0], exe)
                         else
                             null;
@@ -798,7 +798,7 @@ fn runCommand(
                     }
                 },
                 .darling => |bin_name| {
-                    if (b.enable_darling) {
+                    if (b.graph.enable_darling) {
                         try interp_argv.append(bin_name);
                         try interp_argv.appendSlice(argv);
                     } else {
@@ -806,7 +806,7 @@ fn runCommand(
                     }
                 },
                 .wasmtime => |bin_name| {
-                    if (b.enable_wasmtime) {
+                    if (b.graph.enable_wasmtime) {
                         try interp_argv.append(bin_name);
                         try interp_argv.append("--dir=.");
                         try interp_argv.append(argv[0]);
@@ -1036,7 +1036,7 @@ fn spawnChildAndCollect(
         child.cwd = b.build_root.path;
         child.cwd_dir = b.build_root.handle;
     }
-    child.env_map = self.env_map orelse b.env_map;
+    child.env_map = self.env_map orelse &b.graph.env_map;
     child.request_resource_usage_statistics = true;
 
     child.stdin_behavior = switch (self.stdio) {
diff --git a/lib/std/Build/Step/TranslateC.zig b/lib/std/Build/Step/TranslateC.zig
index c55c5889ef..223b004993 100644
--- a/lib/std/Build/Step/TranslateC.zig
+++ b/lib/std/Build/Step/TranslateC.zig
@@ -121,7 +121,7 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
     const self = @fieldParentPtr(TranslateC, "step", step);
 
     var argv_list = std.ArrayList([]const u8).init(b.allocator);
-    try argv_list.append(b.zig_exe);
+    try argv_list.append(b.graph.zig_exe);
     try argv_list.append("translate-c");
     if (self.link_libc) {
         try argv_list.append("-lc");
diff --git a/lib/std/Build/Step/WriteFile.zig b/lib/std/Build/Step/WriteFile.zig
index 7fcf06249f..aab40a8a5e 100644
--- a/lib/std/Build/Step/WriteFile.zig
+++ b/lib/std/Build/Step/WriteFile.zig
@@ -190,7 +190,7 @@ fn make(step: *Step, prog_node: *std.Progress.Node) !void {
     // If, for example, a hard-coded path was used as the location to put WriteFile
     // files, then two WriteFiles executing in parallel might clobber each other.
 
-    var man = b.cache.obtain();
+    var man = b.graph.cache.obtain();
     defer man.deinit();
 
     // Random bytes to make WriteFile unique. Refresh this with