Refactor `span_simple` selection

The current `span_simple` selection is everything but simple. This
version should have the same functionality as the current `span_simple`
with the difference that a lot of complexity has been removed.

Not only is this code shorter, it should also be significantly easier to
understand with no "magic" to it. This will hopefully prevent us from
having an unmaintainable blob of off-by-one guessing in the repo.

Also removed the `out` file which I used in the original PR because
scrollback is not implemented yet. :)

2 files changed, 34 insertions, 213 deletions

diff --git a/out b/out
deleted file mode 100644
index 667994e3..00000000
--- a/out
+++ /dev/null
@@ -1,104 +0,0 @@
-   Compiling alacritty v0.1.0 (file:///home/undeadleech/programming/rust/alacritty)
-warning: unused variable: `count`
-  --> src/input.rs:69:26
-   |
-69 |     fn scroll(&mut self, count: isize) {}
-   |                          ^^^^^ help: consider using `_count` instead
-   |
-   = note: #[warn(unused_variables)] on by default
-
-warning: unused variable: `previous_scroll_limit`
-   --> src/grid/mod.rs:217:13
-    |
-217 |         let previous_scroll_limit = self.scroll_limit;
-    |             ^^^^^^^^^^^^^^^^^^^^^ help: consider using `_previous_scroll_limit` instead
-
-warning: value assigned to `start` is never read
-   --> src/selection.rs:184:13
-    |
-184 |         let mut start = initial_expansion.start;
-    |             ^^^^^^^^^
-    |
-    = note: #[warn(unused_assignments)] on by default
-
-warning: value assigned to `end` is never read
-   --> src/selection.rs:185:13
-    |
-185 |         let mut end = initial_expansion.end;
-    |             ^^^^^^^
-
-warning: method is never used: `pop`
-  --> src/grid/storage.rs:50:5
-   |
-50 |     pub fn pop(&mut self) -> Option<T> {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: #[warn(dead_code)] on by default
-
-warning: method is never used: `swap`
-  --> src/grid/storage.rs:69:5
-   |
-69 |     pub fn swap(&mut self, a: usize, b: usize) {
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-    Finished dev [unoptimized + debuginfo] target(s) in 9.82 secs
-     Running `target/debug/alacritty`
-thread 'main' panicked at 'attempt to subtract with overflow', src/index.rs:414:17
-stack backtrace:
-   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
-             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
-   1: std::sys_common::backtrace::_print
-             at libstd/sys_common/backtrace.rs:71
-   2: std::panicking::default_hook::{{closure}}
-             at libstd/sys_common/backtrace.rs:59
-             at libstd/panicking.rs:207
-   3: std::panicking::default_hook
-             at libstd/panicking.rs:223
-   4: std::panicking::rust_panic_with_hook
-             at libstd/panicking.rs:402
-   5: std::panicking::begin_panic_fmt
-             at libstd/panicking.rs:349
-   6: rust_begin_unwind
-             at libstd/panicking.rs:325
-   7: core::panicking::panic_fmt
-             at libcore/panicking.rs:72
-   8: core::panicking::panic
-             at libcore/panicking.rs:51
-   9: <alacritty::index::Column as core::ops::arith::SubAssign<usize>>::sub_assign
-             at src/index.rs:414
-  10: alacritty::selection::Selection::span_simple
-             at src/selection.rs:283
-  11: alacritty::selection::Selection::to_span
-             at src/selection.rs:167
-  12: alacritty::term::Term::renderable_cells::{{closure}}
-             at src/term/mod.rs:1058
-  13: <core::option::Option<T>>::and_then
-             at /checkout/src/libcore/option.rs:612
-  14: alacritty::term::Term::renderable_cells
-             at src/term/mod.rs:1057
-  15: alacritty::display::Display::draw::{{closure}}
-             at src/display.rs:368
-  16: alacritty::renderer::QuadRenderer::with_api
-             at src/renderer/mod.rs:658
-  17: alacritty::display::Display::draw
-             at src/display.rs:360
-  18: alacritty::run
-             at src/main.rs:203
-  19: alacritty::main
-             at src/main.rs:62
-  20: std::rt::lang_start::{{closure}}
-             at /checkout/src/libstd/rt.rs:74
-  21: std::panicking::try::do_call
-             at libstd/rt.rs:59
-             at libstd/panicking.rs:306
-  22: __rust_maybe_catch_panic
-             at libpanic_unwind/lib.rs:102
-  23: std::rt::lang_start_internal
-             at libstd/panicking.rs:285
-             at libstd/panic.rs:361
-             at libstd/rt.rs:58
-  24: std::rt::lang_start
-             at /checkout/src/libstd/rt.rs:74
-  25: main
-  26: __libc_start_main
-  27: _start
diff --git a/src/selection.rs b/src/selection.rs
index f775f1f6..20b1d601 100644
--- a/src/selection.rs
+++ b/src/selection.rs
@@ -245,127 +245,52 @@ impl Selection {
     }
 
     fn span_simple<G: Dimensions>(grid: &G, region: &Range<Anchor>) -> Option<Span> {
-        let mut start = region.start.point;
+        let start = region.start.point;
         let start_side = region.start.side;
-        let mut end = region.end.point;
+        let end = region.end.point;
         let end_side = region.end.side;
         let cols = grid.dimensions().col;
 
-        // Handle some edge cases
-        if start.line > end.line {
-            if end.col > Column(0) {
-                start.col += 1;
-                end.col -= 1;
-            }
-            // Special case for when a multi-line selection to the
-            // bottom ends on a new line with just one cell selected
-            // and the first cell should not be selected
-            else {
-                if start_side == Side::Right {
-                    start.col += 1;
-                }
-
-                // Remove the single selected cell if mouse left window
-                if end_side == Side::Left {
-                    end.line += 1;
-                    end.col = cols - 1;
-                }
-
-                return Some(Span {
-                    cols,
-                    front: end,
-                    tail: start,
-                    ty: SpanType::Inclusive,
-                });
-            }
-        } else if start.line < end.line {
-            end.col += 1;
-            if start.col > Column(0) {
-                start.col -= 1;
-            }
-            // Special case for when a selection is started
-            // in the first cell of a line
-            else {
-                let ty = match end_side {
-                    Side::Left => SpanType::ExcludeTail,
-                    Side::Right => SpanType::Inclusive,
-                };
-
-                // Switch start cell to last cell of previous line
-                if start_side == Side::Left {
-                    start.line += 1;
-                    start.col = cols - 1;
-                }
-
-                return Some(Span {
-                    ty,
-                    cols,
-                    front: start,
-                    tail: end,
-                });
-            }
+        // No selection for single cell with identical sides or two cell with right+left sides
+        if (start == end && start_side == end_side)
+            || (start_side == Side::Right && end_side == Side::Left && end.col == start.col + 1)
+        {
+            return None;
         }
 
-        let (front, tail, front_side, tail_side) = if start > end {
-            // Selected upward; start/end are swapped
-            (end, start, end_side, start_side)
-        } else {
-            // Selected downward; no swapping
-            (start, end, start_side, end_side)
-        };
-
-        debug_assert!(!(tail < front));
-
-        // Single-cell selections are a special case
-        if start == end {
-            if start_side == end_side {
-                return None;
+        // Make sure front is always the "bottom" and tail is always the "top"
+        let (mut front, mut tail, front_side, tail_side) =
+            if start.line > end.line || start.line == end.line && start.col <= end.col {
+                // Selected upward; start/end are swapped
+                (end, start, end_side, start_side)
             } else {
-                return Some(Span {
-                    cols,
-                    ty: SpanType::Inclusive,
-                    front,
-                    tail,
-                });
+                // Selected downward; no swapping
+                (start, end, start_side, end_side)
+            };
+
+        // Remove last cell if selection ends to the left of a cell
+        if front_side == Side::Left && start != end {
+            if front.col != Column(0) {
+                front.col -= 1;
+            }
+            // Special case when selection starts to left of first cell
+            else {
+                front.col = cols - 1;
+                front.line += 1;
             }
         }
 
-        // The other special case is two adjacent cells with no
-        // selection: [ B][E ] or [ E][B ]
-        let adjacent = tail.line == front.line && tail.col - front.col == Column(1);
-        if adjacent && front_side == Side::Right && tail_side == Side::Left {
-            return None;
+        // Remove first cell if selection starts at the right of a cell
+        if tail_side == Side::Right && front != tail {
+            tail.col += 1;
         }
 
-        Some(match (front_side, tail_side) {
-            // [FX][XX][XT]
-            (Side::Left, Side::Right) => Span {
-                cols,
-                front,
-                tail,
-                ty: SpanType::Inclusive
-            },
-            // [ F][XX][T ]
-            (Side::Right, Side::Left) => Span {
-                cols,
-                front,
-                tail,
-                ty: SpanType::Exclusive
-            },
-            // [FX][XX][T ]
-            (Side::Left, Side::Left) => Span {
-                cols,
-                front,
-                tail,
-                ty: SpanType::ExcludeTail
-            },
-            // [ F][XX][XT]
-            (Side::Right, Side::Right) => Span {
-                cols,
-                front,
-                tail,
-                ty: SpanType::ExcludeFront
-            },
+        // Return the selection with all cells inclusive
+        Some(Span {
+            cols,
+            front,
+            tail,
+            ty: SpanType::Inclusive,
         })
     }
 }