bump MSRV to 1.70.0 (#8877)

* rust-toolchain.toml: bump MSRV to 1.70.0

With Firefox 120 released on 21 November 2023, the MSRV is now 1.70.0.

* Fix cargo fmt with Rust 1.70.0

* Fix cargo clippy with Rust 1.70.0

* Fix cargo doc with Rust 1.70.0

* rust-toolchain.toml: add clippy component

* .github: bump dtolnay/rust-toolchain to 1.70

* helix-term: bump rust-version to 1.70

* helix-view/gutter: use checked_ilog10 to count digits

* helix-core/syntax: use MAIN_SEPARATOR_STR constant

* helix-view/handlers/dap: use Display impl for displaying process spawn error

* WIP: helix-term/commands: use checked math to assert ranges cannot overlap

1 files changed, 11 insertions, 5 deletions

diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index bc54abaa..cd053266 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -1318,7 +1318,7 @@ fn extend_next_long_word_end(cx: &mut Context) {
     extend_word_impl(cx, movement::move_next_long_word_end)
 }
 
-/// Separate branch to find_char designed only for <ret> char.
+/// Separate branch to find_char designed only for `<ret>` char.
 //
 // This is necessary because the one document can have different line endings inside. And we
 // cannot predict what character to find when <ret> is pressed. On the current line it can be `lf`
@@ -5606,12 +5606,18 @@ fn shell(cx: &mut compositor::Context, cmd: &str, behavior: &ShellBehavior) {
         };
 
         // These `usize`s cannot underflow because selection ranges cannot overlap.
-        // Once the MSRV is 1.66.0 (mixed_integer_ops is stabilized), we can use checked
-        // arithmetic to assert this.
-        let anchor = (to as isize + offset - deleted_len as isize) as usize;
+        let anchor = to
+            .checked_add_signed(offset)
+            .expect("Selection ranges cannot overlap")
+            .checked_sub(deleted_len)
+            .expect("Selection ranges cannot overlap");
         let new_range = Range::new(anchor, anchor + output_len).with_direction(range.direction());
         ranges.push(new_range);
-        offset = offset + output_len as isize - deleted_len as isize;
+        offset = offset
+            .checked_add_unsigned(output_len)
+            .expect("Selection ranges cannot overlap")
+            .checked_sub_unsigned(deleted_len)
+            .expect("Selection ranges cannot overlap");
 
         changes.push((from, to, Some(output)));
     }