From 68ba84d9001e4ad3307aebbcbbbe213d99b1e12b Mon Sep 17 00:00:00 2001
From: Philip Metzger <philipmetzger@bluewin.ch>
Date: Wed, 8 Nov 2023 20:15:16 +0100
Subject: [PATCH] run: Fix up various things.

Adress the post-merge comments from #2486, which found a doc comment
inaccurate and to not blindly ignore `-j 0` which would've worked until now.
I've also reduced the default `jobs` size to one, as it's user-visible configuration
which determines how many processes should run.

Thanks to @necauqua the controversial `unsafe` usage was already removed.

I've omitted to change `revisions` from an Vec to a RevisonArg for the moment,
as I will keep working on the file anyway.
---
 cli/src/commands/run.rs | 28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/cli/src/commands/run.rs b/cli/src/commands/run.rs
index cd343d490a8..7baf6b057fa 100644
--- a/cli/src/commands/run.rs
+++ b/cli/src/commands/run.rs
@@ -14,8 +14,6 @@
 
 //! This file contains the internal implementation of `run`.
 
-use std::num::NonZeroUsize;
-
 use crate::cli_util::{
     resolve_multiple_nonempty_revsets, user_error, CommandError, CommandHelper, RevisionArg,
 };
@@ -39,8 +37,6 @@ pub struct RunArgs {
     /// The command to run across all selected revisions.
     shell_command: String,
     /// The revisions to change.
-    /// Multiple revsets are accepted and the work will be done on a
-    /// intersection of them.
     #[arg(long, short, default_value = "@")]
     revisions: Vec<RevisionArg>,
     /// A no-op option to match the interface of `git rebase -x`.
@@ -55,16 +51,18 @@ pub fn cmd_run(ui: &mut Ui, command: &CommandHelper, args: &RunArgs) -> Result<(
     let workspace_command = command.workspace_helper(ui)?;
     let _resolved_commits =
         resolve_multiple_nonempty_revsets(&args.revisions, &workspace_command, ui)?;
-    let _jobs = if let Some(_jobs) = args.jobs {
-        _jobs
-    } else {
-        // Use all available cores
-
-        // SAFETY:
-        // We use a internal constant of 4 threads, if it fails
-        let available =
-            std::thread::available_parallelism().unwrap_or(NonZeroUsize::new(4).unwrap());
-        available.into()
-    };
+    // Jobs are resolved in this order:
+    // 1. Commandline argument iff > 0.
+    // 2. the amount of cores available.
+    // 3. a single job, if all of the above fails.
+    let _jobs = match args.jobs {
+        Some(0) => return Err(user_error("must pass atleast one job")),
+        Some(jobs) => Some(jobs),
+        None => std::thread::available_parallelism()
+            .ok()
+            .and_then(|t| t.try_into().ok()),
+    }
+    // Fallback to a single user-visible job.
+    .unwrap_or(1usize);
     Err(user_error("This is a stub, do not use"))
 }