Added punctuation preference

Create test.rs

Delete test.rs

Fixed compile error.

Trying a possible fix on an arithmetic overflow

another try at the test failure...

passed all tests.

Added tests and cleaned up logic as per nrc's critiques

Delete string.rs.old

Delete string.rs.bk

Made changes as per nrc's requests.

Update string_punctuation.rs

Update string_punctuation.rs

fixed logical redundancy

src/string.rs

@@ -39,6 +39,7 @@ pub fn rewrite_string<'a>(s: &str, fmt: &StringFormat<'a>) -> Option<String> {
 
     let graphemes = UnicodeSegmentation::graphemes(&*stripped_str, false).collect::<Vec<&str>>();
     let indent = fmt.offset.to_string(fmt.config);
+    let punctuation = ":,;.";
 
     let mut cur_start = 0;
     let mut result = String::with_capacity(round_up_to_power_of_two(s.len()));
@@ -62,11 +63,22 @@ pub fn rewrite_string<'a>(s: &str, fmt: &StringFormat<'a>) -> Option<String> {
         while !graphemes[cur_end - 1].trim().is_empty() {
             cur_end -= 1;
             if cur_end - cur_start < MIN_STRING {
-                // We can't break at whitespace, fall back to splitting
-                // anywhere that doesn't break an escape sequence.
                 cur_end = cur_start + max_chars;
-                while graphemes[cur_end - 1] == "\\" {
-                    cur_end -= 1;
+                // Look for punctuation to break on.
+                while (!punctuation.contains(graphemes[cur_end - 1])) && cur_end > 1 {
+                    if cur_end > 1 {
+                        cur_end -= 1;
+                    }
+                }
+                // We can't break at whitespace or punctuation, fall back to splitting
+                // anywhere that doesn't break an escape sequence.
+                if cur_end < cur_start + MIN_STRING {
+                    cur_end = cur_start + max_chars;
+                    while graphemes[cur_end - 1] == "\\" {
+                        if cur_end > 1 {
+                            cur_end -= 1;
+                        }
+                    }
                 }
                 break;
             }

tests/source/string_punctuation.rs

@@ -0,0 +1,5 @@
+fn main() {
+    println!("ThisIsAReallyLongStringWithNoSpaces.It_should_prefer_to_break_onpunctuation:Likethisssssssssssss");
+    format!("{}__{}__{}ItShouldOnlyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyNoticeSemicolonsPeriodsColonsAndCommasAndResortToMid-CharBreaksAfterPunctuation{}{}",x,y,z,a,b);
+    println!("aaaaaaaaaaaaaaaaaaaaaaaaaaaaalhijalfhiigjapdighjapdigjapdighdapighapdighpaidhg;adopgihadoguaadbadgad,qeoihapethae8t0aet8haetadbjtaeg;ooeouthaoeutgadlgajduabgoiuadogabudogubaodugbadgadgadga;adoughaoeugbaouea");
+}

tests/target/string_punctuation.rs

@@ -0,0 +1,14 @@
+fn main() {
+    println!("ThisIsAReallyLongStringWithNoSpaces.It_should_prefer_to_break_onpunctuation:\
+              Likethisssssssssssss");
+    format!("{}__{}__{}ItShouldOnlyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyNoticeSemicolonsPeriodsColo\
+             nsAndCommasAndResortToMid-CharBreaksAfterPunctuation{}{}",
+            x,
+            y,
+            z,
+            a,
+            b);
+    println!("aaaaaaaaaaaaaaaaaaaaaaaaaaaaalhijalfhiigjapdighjapdigjapdighdapighapdighpaidhg;\
+              adopgihadoguaadbadgad,qeoihapethae8t0aet8haetadbjtaeg;\
+              ooeouthaoeutgadlgajduabgoiuadogabudogubaodugbadgadgadga;adoughaoeugbaouea");
+}