Expose a proper `--display` CLI option

This helps with discovery of the different display options available,
such as inline (see #34).

CHANGELOG.md

@@ -1,5 +1,11 @@
 ## 0.26 (unreleased)
 
+### Command Line Interface
+
+Added the `--display` option to switch between `side-by-side`,
+`side-by-side-show-both`, and `inline` display modes. This replaces
+the `INLINE` and `DFT_SHOW_BOTH` environment variables.
+
 ## 0.25 (released 31st March 2022)
 
 ### Display

src/main.rs

@@ -50,7 +50,7 @@ use mimalloc::MiMalloc;
 #[global_allocator]
 static GLOBAL: MiMalloc = MiMalloc;
 
-use options::{should_use_color, Mode};
+use options::{should_use_color, DisplayMode, Mode};
 use sliders::fix_all_sliders;
 use std::{env, path::Path};
 use style::BackgroundColor;
@@ -126,6 +126,7 @@ fn main() {
             byte_limit,
             print_unchanged,
             missing_as_empty,
+            display_mode,
             background_color,
             color_output,
             display_width,
@@ -157,6 +158,7 @@ fn main() {
                     print_diff_result(
                         display_width,
                         use_color,
+                        display_mode,
                         background_color,
                         print_unchanged,
                         &diff_result,
@@ -174,6 +176,7 @@ fn main() {
                 print_diff_result(
                     display_width,
                     use_color,
+                    display_mode,
                     background_color,
                     print_unchanged,
                     &diff_result,
@@ -370,6 +373,7 @@ fn diff_directories<'a>(
 fn print_diff_result(
     display_width: usize,
     use_color: bool,
+    display_mode: DisplayMode,
     background: BackgroundColor,
     print_unchanged: bool,
     summary: &DiffResult,
@@ -406,31 +410,35 @@ fn print_diff_result(
                 return;
             }
 
-            if env::var("INLINE").is_ok() {
-                inline::print(
-                    lhs_src,
-                    rhs_src,
-                    &summary.lhs_positions,
-                    &summary.rhs_positions,
-                    &hunks,
-                    &summary.path,
-                    &lang_name,
-                    use_color,
-                    background,
-                );
-            } else {
-                side_by_side::print(
-                    &hunks,
-                    display_width,
-                    use_color,
-                    background,
-                    &summary.path,
-                    &lang_name,
-                    lhs_src,
-                    rhs_src,
-                    &summary.lhs_positions,
-                    &summary.rhs_positions,
-                );
+            match display_mode {
+                DisplayMode::Inline => {
+                    inline::print(
+                        lhs_src,
+                        rhs_src,
+                        &summary.lhs_positions,
+                        &summary.rhs_positions,
+                        &hunks,
+                        &summary.path,
+                        &lang_name,
+                        use_color,
+                        background,
+                    );
+                }
+                DisplayMode::SideBySide | DisplayMode::SideBySideShowBoth => {
+                    side_by_side::print(
+                        &hunks,
+                        display_width,
+                        use_color,
+                        display_mode,
+                        background,
+                        &summary.path,
+                        &lang_name,
+                        lhs_src,
+                        rhs_src,
+                        &summary.lhs_positions,
+                        &summary.rhs_positions,
+                    );
+                }
             }
         }
         (FileContent::Binary(lhs_bytes), FileContent::Binary(rhs_bytes)) => {

src/options.rs

@@ -1,4 +1,4 @@
-use std::env;
+use std::{borrow::Borrow, env};
 
 use atty::Stream;
 use clap::{crate_authors, crate_description, crate_version, App, AppSettings, Arg};
@@ -63,6 +63,12 @@ fn app() -> clap::App<'static> {
                 .validator(|s| s.parse::<usize>())
                 .required(false),
         )
+        .arg(
+            Arg::new("display").long("display")
+                .possible_values(["side-by-side", "side-by-side-show-both", "inline", ])
+                .value_name("MODE")
+                .help("Display mode for showing results. Overrides $DFT_DISPLAY if present.")
+        )
         .arg(
             Arg::new("color").long("color")
                 .possible_values(["always", "auto", "never"])
@@ -111,12 +117,20 @@ fn app() -> clap::App<'static> {
         .setting(AppSettings::ArgRequiredElseHelp)
 }
 
+#[derive(Debug, Copy, Clone)]
+pub enum DisplayMode {
+    Inline,
+    SideBySide,
+    SideBySideShowBoth,
+}
+
 pub enum Mode {
     Diff {
         node_limit: u32,
         byte_limit: usize,
         print_unchanged: bool,
         missing_as_empty: bool,
+        display_mode: DisplayMode,
         background_color: BackgroundColor,
         color_output: ColorOutput,
         display_width: usize,
@@ -205,6 +219,22 @@ pub fn parse_args() -> Mode {
         env_width.unwrap_or_else(detect_display_width)
     };
 
+    let display_mode_str = if let Some(display_mode_str) = matches.value_of("display") {
+        display_mode_str.to_owned()
+    } else {
+        env::var("DFT_DISPLAY").unwrap_or_else(|_| "".to_owned())
+    };
+    let display_mode = match display_mode_str.borrow() {
+        "side-by-side" => DisplayMode::SideBySide,
+        "side-by-side-show-both" => DisplayMode::SideBySideShowBoth,
+        "inline" => DisplayMode::Inline,
+        _ => {
+            // The CLI validates values, but environment variables can
+            // be any string.
+            DisplayMode::SideBySide
+        }
+    };
+
     let color_output = if let Some(color_when) = matches.value_of("color") {
         if color_when == "always" {
             ColorOutput::Always
@@ -274,6 +304,7 @@ pub fn parse_args() -> Mode {
         byte_limit,
         print_unchanged,
         missing_as_empty,
+        display_mode,
         background_color,
         color_output,
         display_width,

src/side_by_side.rs

@@ -10,6 +10,7 @@ use crate::{
     context::all_matched_lines_filled,
     hunks::{matched_lines_for_hunk, Hunk},
     lines::{codepoint_len, format_line_num, LineNumber},
+    options::DisplayMode,
     positions::SingleLineSpan,
     style::{self, apply_colors, color_positions, novel_style, split_and_apply, BackgroundColor},
     syntax::{zip_pad_shorter, MatchedPos},
@@ -302,6 +303,7 @@ pub fn print(
     hunks: &[Hunk],
     display_width: usize,
     use_color: bool,
+    display_mode: DisplayMode,
     background: BackgroundColor,
     display_path: &str,
     lang_name: &str,
@@ -413,7 +415,8 @@ pub fn print(
                 prev_rhs_line_num,
             );
 
-            if no_lhs_changes && !std::env::var("DFT_SHOW_BOTH").is_ok() {
+            let show_both = matches!(display_mode, DisplayMode::SideBySideShowBoth);
+            if no_lhs_changes && !show_both {
                 match rhs_line_num {
                     Some(rhs_line_num) => {
                         let rhs_line = &rhs_colored_lines[rhs_line_num.0];
@@ -433,7 +436,7 @@ pub fn print(
                         println!("{}{}", display_rhs_line_num, display_rhs_line_num);
                     }
                 }
-            } else if no_rhs_changes && !std::env::var("DFT_SHOW_BOTH").is_ok() {
+            } else if no_rhs_changes && !show_both {
                 match lhs_line_num {
                     Some(lhs_line_num) => {
                         let lhs_line = &lhs_colored_lines[lhs_line_num.0];
@@ -686,6 +689,7 @@ mod tests {
             &hunks,
             80,
             true,
+            DisplayMode::SideBySide,
             BackgroundColor::Dark,
             "foo.el",
             "Emacs Lisp",