Handle combined diff format

With this commit combined diff
format (https://git-scm.com/docs/git-diff#_combined_diff_format) is
handled appropriately. However, there is no special handling of merge
conflict markers.

Fixes #189, #736

15 files changed, 196 insertions, 125 deletions

diff --git a/src/config.rs b/src/config.rs
index af9ade09..5858afe5 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -145,11 +145,11 @@ pub struct Config {
 impl Config {
     pub fn get_style(&self, state: &State) -> &Style {
         match state {
-            State::HunkMinus(_) => &self.minus_style,
-            State::HunkPlus(_) => &self.plus_style,
+            State::HunkMinus(_, _) => &self.minus_style,
+            State::HunkPlus(_, _) => &self.plus_style,
             State::CommitMeta => &self.commit_style,
-            State::DiffHeader => &self.file_style,
-            State::HunkHeader(_, _) => &self.hunk_header_style,
+            State::DiffHeader(_) => &self.file_style,
+            State::HunkHeader(_, _, _) => &self.hunk_header_style,
             State::SubmoduleLog => &self.file_style,
             _ => delta_unreachable("Unreachable code reached in get_style."),
         }
diff --git a/src/delta.rs b/src/delta.rs
index bbbce519..3f1a79d4 100644
--- a/src/delta.rs
+++ b/src/delta.rs
@@ -14,17 +14,17 @@ use crate::style::DecorationStyle;
 
 #[derive(Clone, Debug, PartialEq)]
 pub enum State {
-    CommitMeta,                    // In commit metadata section
-    DiffHeader, // In diff header section, between (possible) commit metadata and first hunk
-    HunkHeader(String, String), // In hunk metadata line (line, raw_line)
-    HunkZero,   // In hunk; unchanged line
-    HunkMinus(Option<String>), // In hunk; removed line (raw_line)
-    HunkPlus(Option<String>), // In hunk; added line (raw_line)
-    SubmoduleLog, // In a submodule section, with gitconfig diff.submodule = log
+    CommitMeta,                                // In commit metadata section
+    DiffHeader(DiffType), // In diff metadata section, between (possible) commit metadata and first hunk
+    HunkHeader(DiffType, String, String), // In hunk metadata line (line, raw_line)
+    HunkZero(Option<String>), // In hunk; unchanged line (prefix)
+    HunkMinus(Option<String>, Option<String>), // In hunk; removed line (prefix, raw_line)
+    HunkPlus(Option<String>, Option<String>), // In hunk; added line (prefix, raw_line)
+    SubmoduleLog,         // In a submodule section, with gitconfig diff.submodule = log
     SubmoduleShort(String), // In a submodule section, with gitconfig diff.submodule = short
     Blame(String, Option<String>), // In a line of `git blame` output (commit, repeat_blame_line).
-    GitShowFile, // In a line of `git show $revision:./path/to/file.ext` output
-    Grep,       // In a line of `git grep` output
+    GitShowFile,          // In a line of `git show $revision:./path/to/file.ext` output
+    Grep,                 // In a line of `git grep` output
     Unknown,
     // The following elements are created when a line is wrapped to display it:
     HunkZeroWrapped,  // Wrapped unchanged line
@@ -32,6 +32,12 @@ pub enum State {
     HunkPlusWrapped,  // Wrapped added line
 }
 
+#[derive(Clone, Debug, PartialEq)]
+pub enum DiffType {
+    Unified,
+    Combined(usize), // number of parent commits: https://git-scm.com/docs/git-diff#_combined_diff_format
+}
+
 #[derive(Debug, PartialEq)]
 pub enum Source {
     GitDiff,     // Coming from a `git diff` command
@@ -171,7 +177,9 @@ impl<'a> StateMachine<'a> {
 
     /// Skip file metadata lines unless a raw diff style has been requested.
     pub fn should_skip_line(&self) -> bool {
-        self.state == State::DiffHeader && self.should_handle() && !self.config.color_only
+        matches!(self.state, State::DiffHeader(_))
+            && self.should_handle()
+            && !self.config.color_only
     }
 
     /// Emit unchanged any line that delta does not handle.
@@ -211,7 +219,11 @@ pub fn format_raw_line<'a>(line: &'a str, config: &Config) -> Cow<'a, str> {
 /// * git diff
 /// * diff -u
 fn detect_source(line: &str) -> Source {
-    if line.starts_with("commit ") || line.starts_with("diff --git ") {
+    if line.starts_with("commit ")
+        || line.starts_with("diff --git ")
+        || line.starts_with("diff --cc ")
+        || line.starts_with("diff --combined ")
+    {
         Source::GitDiff
     } else if line.starts_with("diff -u")
         || line.starts_with("diff -ru")
diff --git a/src/features/line_numbers.rs b/src/features/line_numbers.rs
index 0d366f8a..59218f75 100644
--- a/src/features/line_numbers.rs
+++ b/src/features/line_numbers.rs
@@ -76,18 +76,18 @@ pub fn linenumbers_and_styles<'a>(
         config.line_numbers_style_minusplus[Plus],
     );
     let ((minus_number, plus_number), (minus_style, plus_style)) = match state {
-        State::HunkMinus(_) => {
+        State::HunkMinus(_, _) => {
             line_numbers_data.line_number[Left] += increment as usize;
             ((Some(nr_left), None), (minus_style, plus_style))
         }
         State::HunkMinusWrapped => ((None, None), (minus_style, plus_style)),
-        State::HunkZero => {
+        State::HunkZero(_) => {
             line_numbers_data.line_number[Left] += increment as usize;
             line_numbers_data.line_number[Right] += increment as usize;
             ((Some(nr_left), Some(nr_right)), (zero_style, zero_style))
         }
         State::HunkZeroWrapped => ((None, None), (zero_style, zero_style)),
-        State::HunkPlus(_) => {
+        State::HunkPlus(_, _) => {
             line_numbers_data.line_number[Right] += increment as usize;
             ((None, Some(nr_right)), (minus_style, plus_style))
         }
diff --git a/src/features/side_by_side.rs b/src/features/side_by_side.rs
index f4960d76..85b066cb 100644
--- a/src/features/side_by_side.rs
+++ b/src/features/side_by_side.rs
@@ -180,7 +180,7 @@ pub fn paint_minus_and_plus_lines_side_by_side(
             &lines_have_homolog[Left],
             match minus_line_index {
                 Some(i) => &line_states[Left][i],
-                None => &State::HunkMinus(None),
+                None => &State::HunkMinus(None, None),
             },
             &mut Some(line_numbers_data),
             bg_should_fill[Left],
@@ -201,7 +201,7 @@ pub fn paint_minus_and_plus_lines_side_by_side(
             &lines_have_homolog[Right],
             match plus_line_index {
                 Some(i) => &line_states[Right][i],
-                None => &State::HunkPlus(None),
+                None => &State::HunkPlus(None, None),
             },
             &mut Some(line_numbers_data),
             bg_should_fill[Right],
@@ -222,7 +222,7 @@ pub fn paint_zero_lines_side_by_side<'a>(
     painted_prefix: Option<ansi_term::ANSIString>,
     background_color_extends_to_terminal_width: BgShouldFill,
 ) {
-    let states = vec![State::HunkZero];
+    let states = vec![State::HunkZero(None)];
 
     let (states, syntax_style_sections, diff_style_sections) = wrap_zero_block(
         config,
@@ -418,8 +418,8 @@ fn paint_minus_or_plus_panel_line<'a>(
             )
         } else {
             let opposite_state = match state {
-                State::HunkMinus(x) => State::HunkPlus(x.clone()),
-                State::HunkPlus(x) => State::HunkMinus(x.clone()),
+                State::HunkMinus(_, s) => State::HunkPlus(None, s.clone()),
+                State::HunkPlus(_, s) => State::HunkMinus(None, s.clone()),
                 _ => unreachable!(),
             };
             (
@@ -470,17 +470,17 @@ fn pad_panel_line_to_width<'a>(
     // to form the other half of the line, then don't emit the empty line marker.
     if panel_line_is_empty && line_index.is_some() {
         match state {
-            State::HunkMinus(_) => Painter::mark_empty_line(
+            State::HunkMinus(_, _) => Painter::mark_empty_line(
                 &config.minus_empty_line_marker_style,
                 panel_line,
                 Some(" "),
             ),
-            State::HunkPlus(_) => Painter::mark_empty_line(
+            State::HunkPlus(_, _) => Painter::mark_empty_line(
                 &config.plus_empty_line_marker_style,
                 panel_line,
                 Some(" "),
             ),
-            State::HunkZero => {}
+            State::HunkZero(_) => {}
             _ => unreachable!(),
         };
     };
diff --git a/src/handlers/diff_header.rs b/src/handlers/diff_header.rs
index e2888797..1a703393 100644
--- a/src/handlers/diff_header.rs
+++ b/src/handlers/diff_header.rs
@@ -5,7 +5,7 @@ use unicode_segmentation::UnicodeSegmentation;
 
 use super::draw;
 use crate::config::Config;
-use crate::delta::{Source, State, StateMachine};
+use crate::delta::{DiffType, Source, State, StateMachine};
 use crate::features;
 use crate::paint::Painter;
 
@@ -24,7 +24,7 @@ pub enum FileEvent {
 impl<'a> StateMachine<'a> {
     #[inline]
     fn test_diff_header_minus_line(&self) -> bool {
-        (self.state == State::DiffHeader || self.source == Source::DiffUnified)
+        (matches!(self.state, State::DiffHeader(_)) || self.source == Source::DiffUnified)
             && (self.line.starts_with("--- ")
                 || self.line.starts_with("rename from ")
                 || self.line.starts_with("copy from ")
@@ -57,7 +57,7 @@ impl<'a> StateMachine<'a> {
         self.minus_file_event = file_event;
 
         if self.source == Source::DiffUnified {
-            self.state = State::DiffHeader;
+            self.state = State::DiffHeader(DiffType::Unified);
             self.painter
                 .set_syntax(get_file_extension_from_marker_line(&self.line));
         } else {
@@ -85,7 +85,7 @@ impl<'a> StateMachine<'a> {
 
     #[inline]
     fn test_diff_header_plus_line(&self) -> bool {
-        (self.state == State::DiffHeader || self.source == Source::DiffUnified)
+        (matches!(self.state, State::DiffHeader(_)) || self.source == Source::DiffUnified)
             && (self.line.starts_with("+++ ")
                 || self.line.starts_with("rename to ")
                 || self.line.starts_with("copy to ")
diff --git a/src/handlers/diff_header_diff.rs b/src/handlers/diff_header_diff.rs
index 78ec2a98..869e40ef 100644
--- a/src/handlers/diff_header_diff.rs
+++ b/src/handlers/diff_header_diff.rs
@@ -1,4 +1,4 @@
-use crate::delta::{State, StateMachine};
+use crate::delta::{DiffType, State, StateMachine};
 
 impl<'a> StateMachine<'a> {
     #[inline]
@@ -12,7 +12,12 @@ impl<'a> StateMachine<'a> {
             return Ok(false);
         }
         self.painter.paint_buffered_minus_and_plus_lines();
-        self.state = State::DiffHeader;
+        self.state =
+            if self.line.starts_with("diff --cc ") || self.line.starts_with("diff --combined ") {
+                State::DiffHeader(DiffType::Combined(2)) // We will confirm the number of parents when we see the hunk header
+            } else {
+                State::DiffHeader(DiffType::Unified)
+            };
         self.handled_diff_header_header_line_file_pair = None;
         self.diff_line = self.line.clone();
         if !self.should_skip_line() {
diff --git a/src/handlers/diff_header_misc.rs b/src/handlers/diff_header_misc.rs
index f112d46b..eb0833de 100644
--- a/src/handlers/diff_header_misc.rs
+++ b/src/handlers/diff_header_misc.rs
@@ -1,4 +1,4 @@
-use crate::delta::{Source, State, StateMachine};
+use crate::delta::{DiffType, Source, State, StateMachine};
 
 impl<'a> StateMachine<'a> {
     #[inline]
@@ -11,6 +11,9 @@ impl<'a> StateMachine<'a> {
         if !self.test_diff_header_misc_cases() {
             return Ok(false);
         }
-        self.handle_additional_cases(State::DiffHeader)
+        self.handle_additional_cases(match self.state {
+            State::DiffHeader(_) => self.state.clone(),
+            _ => State::DiffHeader(DiffType::Unified),
+        })
     }
 }
diff --git a/src/handlers/hunk.rs b/src/handlers/hunk.rs
index 75e0bb6f..93ac70ca 100644
--- a/src/handlers/hunk.rs
+++ b/src/handlers/hunk.rs
@@ -1,7 +1,10 @@
+use std::cmp::min;
+
 use lazy_static::lazy_static;
 
 use crate::cli;
-use crate::delta::{State, StateMachine};
+use crate::config::delta_unreachable;
+use crate::delta::{DiffType, State, StateMachine};
 use crate::style;
 use crate::utils::process::{self, CallingProcess};
 use unicode_segmentation::UnicodeSegmentation;
@@ -26,7 +29,10 @@ impl<'a> StateMachine<'a> {
     fn test_hunk_line(&self) -> bool {
         matches!(
             self.state,
-            State::HunkHeader(_, _) | State::HunkZero | State::HunkMinus(_) | State::HunkPlus(_)
+            State::HunkHeader(_, _, _)
+                | State::HunkZero(_)
+                | State::HunkMinus(_, _)
+                | State::HunkPlus(_, _)
         ) && !&*IS_WORD_DIFF
     }
 
@@ -37,6 +43,7 @@ impl<'a> StateMachine<'a> {
     // highlighting according to inferred edit operations. In the case of
     // an unchanged line, we paint it immediately.
     pub fn handle_hunk_line(&mut self) -> std::io::Result<bool> {
+        use State::*;
         // A true hunk line should start with one of: '+', '-', ' '. However, handle_hunk_line
         // handles all lines until the state transitions away from the hunk states.
         if !self.test_hunk_line() {
@@ -50,16 +57,17 @@ impl<'a> StateMachine<'a> {
         {
             self.painter.paint_buffered_minus_and_plus_lines();
         }
-        if let State::HunkHeader(line, raw_line) = &self.state.clone() {
+        if let State::HunkHeader(_, line, raw_line) = &self.state.clone() {
             self.emit_hunk_header_line(line, raw_line)?;
         }
-        self.state = match self.line.chars().next() {
-            Some('-') => {
-                if let State::HunkPlus(_) = self.state {
+        self.state = match new_line_state(&self.line, &self.state) {
+            Some(HunkMinus(prefix, _)) => {
+                if let HunkPlus(_, _) = self.state {
                     // We have just entered a new subhunk; process the previous one
                     // and flush the line buffers.
                     self.painter.paint_buffered_minus_and_plus_lines();
                 }
+                let line = self.painter.prepare(&self.line, prefix.as_deref());
                 let state = match self.config.inspect_raw_lines {
                     cli::InspectRawLines::True
                         if style::line_has_style_other_than(
@@ -67,16 +75,18 @@ impl<'a> StateMachine<'a> {
                             [*style::GIT_DEFAULT_MINUS_STYLE, self.config.git_minus_style].iter(),
                         ) =>
                     {
-                        State::HunkMinus(Some(self.painter.prepare_raw_line(&self.raw_line)))
+                        let raw_line = self
+                            .painter
+                            .prepare_raw_line(&self.raw_line, prefix.as_deref());
+                        HunkMinus(prefix, Some(raw_line))
                     }
-                    _ => State::HunkMinus(None),
+                    _ => HunkMinus(prefix, None),
                 };
-                self.painter
-                    .minus_lines
-                    .push((self.painter.prepare(&self.line), state.clone()));
+                self.painter.minus_lines.push((line, state.clone()));
                 state
             }
-            Some('+') => {
+            Some(HunkPlus(prefix, _)) => {
+                let line = self.painter.prepare(&self.line, prefix.as_deref());
                 let state = match self.config.inspect_raw_lines {
                     cli::InspectRawLines::True
                         if style::line_has_style_other_than(
@@ -84,37 +94,70 @@ impl<'a> StateMachine<'a> {
                             [*style::GIT_DEFAULT_PLUS_STYLE, self.config.git_plus_style].iter(),
                         ) =>
                     {
-                        State::HunkPlus(Some(self.painter.prepare_raw_line(&self.raw_line)))
+                        let raw_line = self
+                            .painter
+                            .prepare_raw_line(&self.raw_line, prefix.as_deref());
+                        HunkPlus(prefix, Some(raw_line))
                     }
-                    _ => State::HunkPlus(None),
+                    _ => HunkPlus(prefix, None),
                 };
-                self.painter
-                    .plus_lines
-                    .push((self.painter.prepare(&self.line), state.clone()));
+                self.painter.plus_lines.push((line, state.clone()));
                 state
             }
-            Some(' ') => {
+            Some(HunkZero(prefix)) => {
+                // We are in a zero (unchanged) line, therefore we have just exited a subhunk (a
+                // sequence of consecutive minus (removed) and/or plus (added) lines). Process that
+                // subhunk and flush the line buffers.
                 self.painter.paint_buffered_minus_and_plus_lines();
-                self.painter.paint_zero_line(&self.line);
-                State::HunkZero
+                self.painter.paint_zero_line(&self.line, prefix.clone());
+                HunkZero(prefix)
             }
             _ => {
                 // The first character here could be e.g. '\' from '\ No newline at end of file'. This
                 // is not a hunk line, but the parser does not have a more accurate state corresponding
                 // to this.
-
-                // We are in a zero (unchanged) line, therefore we have just exited a subhunk (a
-                // sequence of consecutive minus (removed) and/or plus (added) lines). Process that
-                // subhunk and flush the line buffers.
                 self.painter.paint_buffered_minus_and_plus_lines();
                 self.painter
                     .output_buffer
                     .push_str(&self.painter.expand_tabs(self.raw_line.graphemes(true)));
                 self.painter.output_buffer.push('\n');
-                State::HunkZero
+                State::HunkZero(None)
             }
         };
         self.painter.emit()?;
         Ok(true)
     }
 }
+
+fn new_line_state(new_line: &str, prev_state: &State) -> Option<State> {
+    use State::*;
+    let diff_type = match prev_state {
+        HunkMinus(None, _) | HunkZero(None) | HunkPlus(None, _) => DiffType::Unified,
+        HunkHeader(diff_type, _, _) => diff_type.clone(),
+        HunkMinus(Some(prefix), _) | HunkZero(Some(prefix)) | HunkPlus(Some(prefix), _) => {
+            DiffType::Combined(prefix.len())
+        }
+        _ => delta_unreachable(&format!("diff_type: unexpected state: {:?}", prev_state)),
+    };
+
+    let (prefix_char, prefix) = match diff_type {
+        DiffType::Unified => (new_line.chars().next(), None),
+        DiffType::Combined(n_parents) => {
+            let prefix = &new_line[..min(n_parents, new_line.len())];
+            let prefix_char = match prefix.chars().find(|c| c == &'-' || c == &'+') {
+                Some(c) => Some(c),
+                None => match prefix.chars().find(|c| c != &' ') {
+                    None => Some(' '),
+                    Some(_) => None,
+                },
+            };
+            (prefix_char, Some(prefix.to_string()))
+        }
+    };
+    match prefix_char {
+        Some('-') => Some(HunkMinus(prefix, None)),
+        Some(' ') => Some(HunkZero(prefix)),
+        Some('+') => Some(HunkPlus(prefix, None)),
+        _ => None,
+    }
+}
diff --git a/src/handlers/hunk_header.rs b/src/handlers/hunk_header.rs
index dd851509..39c223d6 100644
--- a/src/handlers/hunk_header.rs
+++ b/src/handlers/hunk_header.rs
@@ -26,7 +26,7 @@ use regex::Regex;
 
 use super::draw;
 use crate::config::Config;
-use crate::delta::{self, State, StateMachine};
+use crate::delta::{self, DiffType, State, StateMachine};
 use crate::paint::{self, BgShouldFill, Painter, StyleSectionSpecifier};
 use crate::style::DecorationStyle;
 
@@ -40,7 +40,15 @@ impl<'a> StateMachine<'a> {
         if !self.test_hunk_header_line() {
             return Ok(false);
         }
-        self.state = State::HunkHeader(self.line.clone(), self.raw_line.clone());
+        let diff_type = match &self.state {
+            State::DiffHeader(DiffType::Combined(_)) => {
+                // https://git-scm.com/docs/git-diff#_combined_diff_format
+                let n_parents = self.line.chars().take_while(|c| c == &'@').count() - 1;
+                DiffType::Combined(n_parents)
+            }
+            _ => DiffType::Unified,
+        };
+        self.state = State::HunkHeader(diff_type, self.line.clone(), self.raw_line.clone());
         Ok(true)
     }
 
@@ -251,7 +259,7 @@ fn write_to_output_buffer(
         painter.syntax_highlight_and_paint_line(
             &line,
             StyleSectionSpecifier::Style(config.hunk_header_style),
-            delta::State::HunkHeader("".to_owned(), "".to_owned()),
+            delta::State::HunkHeader(DiffType::Unified, "".to_owned(), "".to_owned()),
             BgShouldFill::No,
         );
         painter.output_buffer.pop(); // trim newline
diff --git a/src/handlers/submodule.rs b/src/handlers/submodule.rs
index 4350c561..04e273e9 100644
--- a/src/handlers/submodule.rs
+++ b/src/handlers/submodule.rs
@@ -18,7 +18,7 @@ impl<'a> StateMachine<'a> {
 
     #[inline]
     fn test_submodule_short_line(&self) -> bool {
-        matches!(self.state, State::HunkHeader(_, _))
+        matches!(self.state, State::HunkHeader(_, _, _))
             && self.line.starts_with("-Subproject commit ")
             || matches!(self.state, State::SubmoduleShort(_))
                 && self.line.starts_with("+Subproject commit ")
@@ -29,7 +29,7 @@ impl<'a> StateMachine<'a> {
             return Ok(false);
         }
         if let Some(commit) = get_submodule_short_commit(&self.line) {
-            if let State::HunkHeader(_, _) = self.state {
+            if let State::HunkHeader(_, _, _) = self.state {
                 self.state = State::SubmoduleShort(commit.to_owned());
             } else if let State::SubmoduleShort(minus_commit) = &self.state {
                 self.painter.emit()?;
diff --git a/src/paint.rs b/src/paint.rs
index 5821ee92..0ef92dbd 100644
--- a/src/paint.rs
+++ b/src/paint.rs
@@ -1,6 +1,7 @@
 use std::collections::HashMap;
 use std::io::Write;
 
+use ansi_term::ANSIString;
 use itertools::Itertools;
 use syntect::easy::HighlightLines;
 use syntect::highlighting::Style as SyntectStyle;
@@ -122,26 +123,33 @@ impl<'p> Painter<'p> {
     // Terminating with newline character is necessary for many of the sublime syntax definitions to
     // highlight correctly.
     // See https://docs.rs/syntect/3.2.0/syntect/parsing/struct.SyntaxSetBuilder.html#method.add_from_folder
-    pub fn prepare(&self, line: &str) -> String {
+    pub fn prepare(&self, line: &str, prefix: Option<&str>) -> String {
         if !line.is_empty() {
             let mut line = line.graphemes(true);
 
-            // The first column contains a -/+/space character, added by git. We remove it now so that
-            // it is not present during syntax highlighting or wrapping. If --keep-plus-minus-markers is
-            // in effect this character is re-inserted in Painter::paint_line.
-            line.next();
+            // The initial columns contain -/+/space characters, added by git. Remove them now so
+            // they are not present during syntax highlighting or wrapping. If
+            // --keep-plus-minus-markers is in effect this prefix is re-inserted in
+            // Painter::paint_line.
+            let prefix_length = prefix.map(|s| s.len()).unwrap_or(1);
+            for _ in 0..prefix_length {
+                line.next();
+            }
             format!("{}\n", self.expand_tabs(line))
         } else {
             "\n".to_string()
         }
     }
 
-    // Remove initial -/+ character, expand tabs as spaces, retaining ANSI sequences. Terminate with
+    // Remove initial -/+ characters, expand tabs as spaces, retaining ANSI sequences. Terminate with
     // newline character.
-    pub fn prepare_raw_line(&self, raw_line: &str) -> String {
+    pub fn prepare_raw_line(&self, raw_line: &str, prefix: Option<&str>) -> String {
         format!(
             "{}\n",
-            ansi::ansi_preserving_slice(&self.expand_tabs(raw_line.graphemes(true)), 1),
+            ansi::ansi_preserving_slice(
+                &self.expand_tabs(raw_line.graphemes(true)),
+                prefix.map(|s| s.len()).unwrap_or(1)
+            ),
         )
     }
 
@@ -207,11 +215,6 @@ impl<'p> Painter<'p> {
                     &mut self.output_buffer,
                     self.config,
                     &mut self.line_numbers_data.as_mut(),
-                    if self.config.keep_plus_minus_markers {
-                        Some(self.config.minus_style.paint("-"))
-                    } else {
-                        None
-                    },
                     Some(self.config.minus_empty_line_marker_style),
                     BgShouldFill::default(),
                 );
@@ -225,11 +228,6 @@ impl<'p> Painter<'p> {
                     &mut self.output_buffer,
                     self.config,
                     &mut self.line_numbers_data.as_mut(),
-                    if self.config.keep_plus_minus_markers {
-                        Some(self.config.plus_style.paint("+"))
-                    } else {
-                        None
-                    },
                     Some(self.config.plus_empty_line_marker_style),
                     BgShouldFill::default(),
                 );
@@ -239,16 +237,10 @@ impl<'p> Painter<'p> {
         self.plus_lines.clear();
     }
 
-    pub fn paint_zero_line(&mut self, line: &str) {
-        let state = State::HunkZero;
-        let painted_prefix = if self.config.keep_plus_minus_markers && !line.is_empty() {
-            // A zero line here still contains the " " prefix, so use it.
-            Some(self.config.zero_style.paint(&line[..1]))
-        } else {
-            None
-        };
-
-        let lines = vec![(self.prepare(line), state)];
+    pub fn paint_zero_line(&mut self, line: &str, prefix: Option<String>) {
+        let line = self.prepare(line, prefix.as_deref());
+        let state = State::HunkZero(prefix);
+        let lines = vec![(line, state.clone())];
         let syntax_style_sections = Painter::get_syntax_style_sections_for_lines(
             &lines,
             self.highlighter.as_mut(),
@@ -265,7 +257,7 @@ impl<'p> Painter<'p> {
                 &mut self.output_buffer,
                 self.config,
                 &mut self.line_numbers_data.as_mut(),
-                painted_prefix,
+                painted_prefix(state, self.config),
                 BgShouldFill::With(BgFillMethod::Spaces),
             );
         } else {
@@ -277,7 +269,6 @@ impl<'p> Painter<'p> {
                 &mut self.output_buffer,
                 self.config,
                 &mut self.line_numbers_data.as_mut(),
-                painted_prefix,
                 None,
                 BgShouldFill::With(BgFillMethod::Spaces),
             );
@@ -295,7 +286,6 @@ impl<'p> Painter<'p> {
         output_buffer: &mut String,
         config: &config::Config,
         line_numbers_data: &mut Option<&mut line_numbers::LineNumbersData>,
-        painted_prefix: Option<ansi_term::ANSIString>,
         empty_line_style: Option<Style>, // a style with background color to highlight an empty line
         background_color_extends_to_terminal_width: BgShouldFill,
     ) {
@@ -318,7 +308,7 @@ impl<'p> Painter<'p> {
                 state,
                 line_numbers_data,
                 None,
-                painted_prefix.clone(),
+                painted_prefix(state.clone(), config),
                 config,
             );
             let (bg_fill_mode, fill_style) =
@@ -384,7 +374,6 @@ impl<'p> Painter<'p> {
             self.config,
             &mut None,
             None,
-            None,
             background_color_extends_to_terminal_width,
         );
     }
@@ -399,22 +388,22 @@ impl<'p> Painter<'p> {
         config: &config::Config,
     ) -> (Option<BgFillMethod>, Style) {
         let fill_style = match state {
-            State::HunkMinus(None) | State::HunkMinusWrapped => {
+            State::HunkMinus(_, None) | State::HunkMinusWrapped => {
                 if let Some(true) = line_has_homolog {
                     config.minus_non_emph_style
                 } else {
                     config.minus_style
                 }
             }
-            State::HunkZero | State::HunkZeroWrapped => config.zero_s