Fix whitespace errors under keep-plus-minus-markers (#425)

* Add failing test of added empty line with keep-plus-minus-markers

* Fix whitespace error flagging with keep-plus-minus-markers

Fixes #388

* Possibly more efficient implementation

* Fix clippy

* Fix clippy II

* Increase tarpaulin timeout

* Increase tarpaulin timeout

* Add failing test of line with one non-whitespace character

* Fix test of line with one non-whitespace character

* Revert tarpaulin changes

2 files changed, 57 insertions, 9 deletions

diff --git a/src/paint.rs b/src/paint.rs
index 7bb19f06..27582194 100644
--- a/src/paint.rs
+++ b/src/paint.rs
@@ -1,5 +1,3 @@
-use lazy_static::lazy_static;
-use regex::Regex;
 use std::io::Write;
 
 use itertools::Itertools;
@@ -586,18 +584,26 @@ fn style_sections_contain_more_than_one_style(sections: &[(Style, &str)]) -> boo
     }
 }
 
-lazy_static! {
-    static ref NON_WHITESPACE_REGEX: Regex = Regex::new(r"\S").unwrap();
-}
-
 /// True iff the line represented by `sections` constitutes a whitespace error.
+// Note that a space is always present as the first character in the line (it was put there as a
+// replacement for the leading +/- marker; see paint::prepare()). A line is a whitespace error iff,
+// beyond the initial space character, (a) there are more characters and (b) they are all
+// whitespace characters.
 // TODO: Git recognizes blank lines at end of file (blank-at-eof) as a whitespace error but delta
 // does not yet.
 // https://git-scm.com/docs/git-config#Documentation/git-config.txt-corewhitespace
 fn is_whitespace_error(sections: &[(Style, &str)]) -> bool {
-    !sections
-        .iter()
-        .any(|(_, s)| NON_WHITESPACE_REGEX.is_match(s))
+    let mut any_chars = false;
+    for c in sections.iter().flat_map(|(_, s)| s.chars()).skip(1) {
+        if c == '\n' {
+            return any_chars;
+        } else if c != ' ' && c != '\t' {
+            return false;
+        } else {
+            any_chars = true;
+        }
+    }
+    false
 }
 
 mod superimpose_style_sections {
diff --git a/src/tests/test_example_diffs.rs b/src/tests/test_example_diffs.rs
index 4fd2184f..6668acce 100644
--- a/src/tests/test_example_diffs.rs
+++ b/src/tests/test_example_diffs.rs
@@ -1303,6 +1303,32 @@ impl<'a> Alignment<'a> { │
     }
 
     #[test]
+    fn test_added_empty_line_is_not_whitespace_error() {
+        let plus_style = "bold yellow red ul";
+        let config = integration_test_utils::make_config_from_args(&[
+            "--light",
+            "--keep-plus-minus-markers",
+            "--plus-style",
+            plus_style,
+        ]);
+        let output = integration_test_utils::run_delta(DIFF_WITH_ADDED_EMPTY_LINE, &config);
+        ansi_test_utils::assert_line_has_style(&output, 6, "", plus_style, &config)
+    }
+
+    #[test]
+    fn test_single_character_line_is_not_whitespace_error() {
+        let plus_style = "bold yellow red ul";
+        let config = integration_test_utils::make_config_from_args(&[
+            "--light",
+            "--keep-plus-minus-markers",
+            "--plus-style",
+            plus_style,
+        ]);
+        let output = integration_test_utils::run_delta(DIFF_WITH_SINGLE_CHARACTER_LINE, &config);
+        ansi_test_utils::assert_line_has_style(&output, 12, "+}", plus_style, &config)
+    }
+
+    #[test]
     fn test_color_only() {
         let config = integration_test_utils::make_config_from_args(&["--color-only"]);
         let output = integration_test_utils::run_delta(GIT_DIFF_SINGLE_HUNK, &config);
@@ -1850,6 +1876,22 @@ index e69de29..8b13789 100644
 +
 ";
 
+    const DIFF_WITH_SINGLE_CHARACTER_LINE: &str = r"
+diff --git a/Person.java b/Person.java
+new file mode 100644
+index 0000000..c6c830c
+--- /dev/null
++++ b/Person.java
+@@ -0,0 +1,7 @@
++import lombok.Data;
++
++@Data
++public class Person {
++  private Long id;
++  private String name;
++}
+";
+
     const DIFF_WITH_WHITESPACE_ERROR: &str = r"
 diff --git c/a i/a
 new file mode 100644