don't inherit allowed deprecation from parent modules

Inheriting allow-deprecation from parent modules doesn't make too much
sense, so instead make them default to disallow unless otherwise
specified. This allows build system to avoid redundant
`-fno-allow-deprecated` args.

This makes the generated CLIs smaller, and makes zig1.wasm update not
needed.

Also represented `is_root` differently (moved to field of graph).

lib/compiler/build_runner.zig

@@ -80,6 +80,7 @@ pub fn main() !void {
             .query = .{},
             .result = try std.zig.system.resolveTargetQuery(.{}),
         },
+        .root_builder = undefined, // populated below
     };
 
     graph.cache.addPrefix(.{ .path = null, .handle = std.fs.cwd() });
@@ -94,6 +95,7 @@ pub fn main() !void {
         local_cache_directory,
         dependencies.root_deps,
     );
+    graph.root_builder = builder;
 
     var targets = ArrayList([]const u8).init(arena);
     var debug_log_scopes = ArrayList([]const u8).init(arena);

lib/std/Build.zig

@@ -94,9 +94,6 @@ available_deps: AvailableDeps,
 
 release_mode: ReleaseMode,
 
-/// `true` only for the root `Build`; `false` for any `Build` belonging to a dependency.
-is_root: bool = false,
-
 pub const ReleaseMode = enum {
     off,
     any,
@@ -121,10 +118,11 @@ pub const Graph = struct {
     /// Information about the native target. Computed before build() is invoked.
     host: ResolvedTarget,
     incremental: ?bool = null,
-    allow_deprecated: ?bool = null,
     random_seed: u32 = 0,
     dependency_cache: InitializedDepMap = .empty,
     allow_so_scripts: ?bool = null,
+    allow_deprecated: ?bool = null,
+    root_builder: *std.Build,
 };
 
 const AvailableDeps = []const struct { []const u8, []const u8 };
@@ -308,7 +306,6 @@ pub fn create(
         .pkg_hash = "",
         .available_deps = available_deps,
         .release_mode = .off,
-        .is_root = true,
     };
     try b.top_level_steps.put(arena, b.install_tls.step.name, &b.install_tls);
     try b.top_level_steps.put(arena, b.uninstall_tls.step.name, &b.uninstall_tls);

lib/std/Build/Module.zig

@@ -557,10 +557,9 @@ pub fn appendZigProcessFlags(
     try addFlag(zig_args, m.pic, "-fPIC", "-fno-PIC");
     try addFlag(zig_args, m.red_zone, "-mred-zone", "-mno-red-zone");
 
-    if (m.root_source_file != null) {
-        const allow_deprecated = m.owner.graph.allow_deprecated orelse !m.owner.is_root;
-        try addFlag(zig_args, allow_deprecated, "-fallow-deprecated", "-fno-allow-deprecated");
-    }
+    // -fno-allow-deprecated is the CLI default, and not inherited, so only pass the flag if true.
+    const allow_deprecated = m.owner.graph.allow_deprecated orelse (m.owner.graph.root_builder != m.owner);
+    if (allow_deprecated == true) try zig_args.append("-fallow-deprecated");
 
     if (m.dwarf_format) |dwarf_format| {
         try zig_args.append(switch (dwarf_format) {

src/Package/Module.zig

@@ -238,7 +238,6 @@ pub fn create(arena: Allocator, options: CreateOptions) !*Package.Module {
 
     const allow_deprecated = b: {
         if (options.inherited.allow_deprecated) |x| break :b x;
-        if (options.parent) |p| break :b p.allow_deprecated;
         break :b false;
     };