formatter: don't write escape codes until we write text

We often end up writing escape codes for one style and then
immediately after, we write escape codes for another style. That seems
harmless, but it's a little ugly. More importantly, it prepares for
not emitting any escapes for turning off attributes at the end of
formatted contents across multiple lines (see next commit).

src/formatter.rs

@@ -346,6 +346,7 @@ fn color_for_name(color_name: &str) -> Option<Color> {
 
 impl<W: Write> Write for ColorFormatter<W> {
     fn write(&mut self, data: &[u8]) -> Result<usize, Error> {
+        self.write_new_style()?;
         self.output.write(data)
     }
 
@@ -357,12 +358,15 @@ impl<W: Write> Write for ColorFormatter<W> {
 impl<W: Write> Formatter for ColorFormatter<W> {
     fn push_label(&mut self, label: &str) -> io::Result<()> {
         self.labels.push(label.to_owned());
-        self.write_new_style()
+        Ok(())
     }
 
     fn pop_label(&mut self) -> io::Result<()> {
         self.labels.pop();
-        self.write_new_style()
+        if self.labels.is_empty() {
+            self.write_new_style()?
+        }
+        Ok(())
     }
 }
 
@@ -511,7 +515,7 @@ mod tests {
          bold only 
          underlined only 
          single rule 
-         two rules 
+         two rules 
         "###);
     }
 

tests/test_commit_template.rs

@@ -80,7 +80,7 @@ fn test_log_default() {
     | 
     o 9a45c67d3e96 test.user@example.com 2001-02-03 04:05:08.000 +07:00 4291e264ae97
     | add a file
-    o 000000000000  1970-01-01 00:00:00.000 +00:00 000000000000
+    o 000000000000  1970-01-01 00:00:00.000 +00:00 000000000000
       (no description set)
     "###);
 
@@ -91,7 +91,7 @@ fn test_log_default() {
     description 1
     9a45c67d3e96 test.user@example.com 2001-02-03 04:05:08.000 +07:00 4291e264ae97
     add a file
-    000000000000  1970-01-01 00:00:00.000 +00:00 000000000000
+    000000000000  1970-01-01 00:00:00.000 +00:00 000000000000
     (no description set)
     "###);
 }
@@ -138,7 +138,7 @@ fn test_log_default_divergence() {
     | @ 9a45c67d3e96?? test.user@example.com 2001-02-03 04:05:08.000 +07:00 7a17d52e633c
     |/  description 1
     |   
-    o 000000000000  1970-01-01 00:00:00.000 +00:00 000000000000
+    o 000000000000  1970-01-01 00:00:00.000 +00:00 000000000000
       (no description set)
     "###);
 }

tests/test_global_opts.rs

@@ -182,7 +182,7 @@ fn test_color_config() {
     // Test that --color=always is respected.
     let stdout = test_env.jj_cmd_success(&repo_path, &["--color=always", "log", "-T", "commit_id"]);
     insta::assert_snapshot!(stdout, @r###"
-    @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
     o 0000000000000000000000000000000000000000
     "###);
 
@@ -193,7 +193,7 @@ color="always""#,
     );
     let stdout = test_env.jj_cmd_success(&repo_path, &["log", "-T", "commit_id"]);
     insta::assert_snapshot!(stdout, @r###"
-    @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
     o 0000000000000000000000000000000000000000
     "###);
 
@@ -249,7 +249,7 @@ color="always""#,
     test_env.add_env_var("NO_COLOR", "");
     let stdout = test_env.jj_cmd_success(&repo_path, &["log", "-T", "commit_id"]);
     insta::assert_snapshot!(stdout, @r###"
-    @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
+    @ 230dd059e1b059aefc0da06a2e5a7dbf22362f22
     o 0000000000000000000000000000000000000000
     "###);
 

tests/test_log_command.rs

@@ -574,7 +574,7 @@ fn test_graph_template_color() {
     // extra line at the end
     insta::assert_snapshot!(stdout, @r###"
     @ single line
-    | 
+    | 
     o first line
     | second line
     | third line

tests/test_resolve_command.rs

@@ -386,7 +386,7 @@ fn test_too_many_parents() {
     // Test warning color
     insta::assert_snapshot!(test_env.jj_cmd_success(&repo_path, &["resolve", "--list", "--color=always"]), 
     @r###"
-    file    3-sided conflict
+    file    3-sided conflict
     "###);
 
     let error = test_env.jj_cmd_failure(&repo_path, &["resolve"]);
@@ -518,7 +518,7 @@ fn test_description_with_dir_and_deletion() {
     // Test warning color. The deletion is fine, so it's not highlighted
     insta::assert_snapshot!(test_env.jj_cmd_success(&repo_path, &["resolve", "--list", "--color=always"]), 
     @r###"
-    file    3-sided conflict including 1 deletion and a directory
+    file    3-sided conflict including 1 deletion and a directory
     "###);
     let error = test_env.jj_cmd_failure(&repo_path, &["resolve"]);
     insta::assert_snapshot!(error, @r###"