Clarify that --ask is meaningless nh ... build or `nh home build …

…--dry`.

This could be considered a bug report instead of a PR. I was confused
for a while why nh was ignoring my `--ask`, but then realized I was
doing `nh home build` instead of `nh home switch`.

It seems like `--ask --dry` is valid for `nh darwin`, so it is allowed.

src/darwin.rs

@@ -17,7 +17,12 @@ impl DarwinArgs {
         use DarwinRebuildVariant::*;
         match self.subcommand {
             DarwinSubcommand::Switch(args) => args.rebuild(Switch),
-            DarwinSubcommand::Build(args) => args.rebuild(Build),
+            DarwinSubcommand::Build(args) => {
+                if args.common.ask || args.common.dry {
+                    bail!("`nh home build` does not support `--ask` or `--dry`");
+                }
+                args.rebuild(Build)
+            }
             DarwinSubcommand::Repl(args) => args.run(),
         }
     }

src/home.rs

@@ -16,7 +16,12 @@ impl interface::HomeArgs {
         use HomeRebuildVariant::*;
         match self.subcommand {
             HomeSubcommand::Switch(args) => args.rebuild(Switch),
-            HomeSubcommand::Build(args) => args.rebuild(Build),
+            HomeSubcommand::Build(args) => {
+                if args.common.ask || args.common.dry {
+                    bail!("`nh home build` does not support `--ask` or `--dry`");
+                }
+                args.rebuild(Build)
+            }
             HomeSubcommand::Repl(args) => args.run(),
         }
     }
@@ -79,6 +84,9 @@ impl HomeRebuildArgs {
         }
 
         if self.common.dry || matches!(variant, Build) {
+            if self.common.ask {
+                info!("--ask has no effect as dry run was requested");
+            }
             return Ok(());
         }
 

src/nixos.rs

@@ -25,7 +25,12 @@ impl interface::OsArgs {
             OsSubcommand::Boot(args) => args.rebuild(Boot),
             OsSubcommand::Test(args) => args.rebuild(Test),
             OsSubcommand::Switch(args) => args.rebuild(Switch),
-            OsSubcommand::Build(args) => args.rebuild(Build),
+            OsSubcommand::Build(args) => {
+                if args.common.ask || args.common.dry {
+                    bail!("`nh os build` does not support `--ask` or `--dry`");
+                }
+                args.rebuild(Build)
+            }
             OsSubcommand::Repl(args) => args.run(),
             OsSubcommand::Info(args) => args.info(),
         }
@@ -112,6 +117,9 @@ impl OsRebuildArgs {
             .run()?;
 
         if self.common.dry || matches!(variant, Build) {
+            if self.common.ask {
+                info!("--ask has no effect as dry run was requested");
+            }
             return Ok(());
         }