std.zig.system.darwin.isSdkInstalled: fix implementation

* don't assert that the child process doesn't crash
* don't give a false negative on warnings printed to stderr

Also fix getSdk from the same file in the same way

Author: andrewrk

lib/std/zig/system/darwin.zig

@@ -8,27 +8,33 @@ pub const macos = @import("darwin/macos.zig");
 
 /// Check if SDK is installed on Darwin without triggering CLT installation popup window.
 /// Note: simply invoking `xcrun` will inevitably trigger the CLT installation popup.
-/// Therefore, we resort to the same tool used by Homebrew, namely, invoking `xcode-select --print-path`
-/// and checking if the status is nonzero or the returned string in nonempty.
-/// https://github.com/Homebrew/brew/blob/e119bdc571dcb000305411bc1e26678b132afb98/Library/Homebrew/brew.sh#L630
+/// Therefore, we resort to invoking `xcode-select --print-path` and checking
+/// if the status is nonzero.
+/// stderr from xcode-select is ignored.
+/// If error.OutOfMemory occurs in Allocator, this function returns null.
 pub fn isSdkInstalled(allocator: Allocator) bool {
-    const argv = &[_][]const u8{ "/usr/bin/xcode-select", "--print-path" };
-    const result = std.ChildProcess.exec(.{ .allocator = allocator, .argv = argv }) catch return false;
+    const result = std.process.Child.exec(.{
+        .allocator = allocator,
+        .argv = &.{ "/usr/bin/xcode-select", "--print-path" },
+    }) catch return false;
+
     defer {
         allocator.free(result.stderr);
         allocator.free(result.stdout);
     }
-    if (result.stderr.len != 0 or result.term.Exited != 0) {
-        // We don't actually care if there were errors as this is best-effort check anyhow.
-        return false;
-    }
-    return result.stdout.len > 0;
+
+    return switch (result.term) {
+        .Exited => |code| if (code == 0) result.stdout.len > 0 else false,
+        else => false,
+    };
 }
 
 /// Detect SDK on Darwin.
 /// Calls `xcrun --sdk <target_sdk> --show-sdk-path` which fetches the path to the SDK sysroot (if any).
 /// Subsequently calls `xcrun --sdk <target_sdk> --show-sdk-version` which fetches version of the SDK.
 /// The caller needs to deinit the resulting struct.
+/// stderr from xcrun is ignored.
+/// If error.OutOfMemory occurs in Allocator, this function returns null.
 pub fn getSdk(allocator: Allocator, target: Target) ?Sdk {
     const is_simulator_abi = target.abi == .simulator;
     const sdk = switch (target.os.tag) {
@@ -40,30 +46,28 @@ pub fn getSdk(allocator: Allocator, target: Target) ?Sdk {
     };
     const path = path: {
         const argv = &[_][]const u8{ "/usr/bin/xcrun", "--sdk", sdk, "--show-sdk-path" };
-        const result = std.ChildProcess.exec(.{ .allocator = allocator, .argv = argv }) catch return null;
+        const result = std.process.Child.exec(.{ .allocator = allocator, .argv = argv }) catch return null;
         defer {
             allocator.free(result.stderr);
             allocator.free(result.stdout);
         }
-        if (result.stderr.len != 0 or result.term.Exited != 0) {
-            // We don't actually care if there were errors as this is best-effort check anyhow
-            // and in the worst case the user can specify the sysroot manually.
-            return null;
+        switch (result.term) {
+            .Exited => |code| if (code != 0) return null,
+            else => return null,
         }
         const path = allocator.dupe(u8, mem.trimRight(u8, result.stdout, "\r\n")) catch return null;
         break :path path;
     };
     const version = version: {
         const argv = &[_][]const u8{ "/usr/bin/xcrun", "--sdk", sdk, "--show-sdk-version" };
-        const result = std.ChildProcess.exec(.{ .allocator = allocator, .argv = argv }) catch return null;
+        const result = std.process.Child.exec(.{ .allocator = allocator, .argv = argv }) catch return null;
         defer {
             allocator.free(result.stderr);
             allocator.free(result.stdout);
         }
-        if (result.stderr.len != 0 or result.term.Exited != 0) {
-            // We don't actually care if there were errors as this is best-effort check anyhow
-            // and in the worst case the user can specify the sysroot manually.
-            return null;
+        switch (result.term) {
+            .Exited => |code| if (code != 0) return null,
+            else => return null,
         }
         const raw_version = mem.trimRight(u8, result.stdout, "\r\n");
         const version = parseSdkVersion(raw_version) orelse Version{