feat(git_branch): add 'only_attached' config bool (#1910)

* feat(git_branch): add 'only_attached' config bool

This adds a new boolean, `only_attached`, to the configuration for
the `git_branch` module. This mirrors the `only_detached` config
value for the `git_commit` module: setting the value to true causes
the module to suppress its output when the user is not on a branch.

This allows users to have either a branch name or a commit hash in
their prompt, as opposed to having either a branch name or the
overly-wordy "HEAD (sha1)".

* Fix formatting

docs/config/README.md

@@ -1030,6 +1030,7 @@ The `git_branch` module shows the active branch of the repo in your current dire
 | `style`             | `"bold purple"`                  | The style for the module.                                                                |
 | `truncation_length` | `2^63 - 1`                       | Truncates a git branch to X graphemes.                                                   |
 | `truncation_symbol` | `"…"`                            | The symbol used to indicate a branch name was truncated. You can use `""` for no symbol. |
+| `only_attached`      | `false`                                         | Only show the branch name when not in a detached HEAD state. |
 | `disabled`          | `false`                          | Disables the `git_branch` module.                                                        |
 
 ### Variables

src/configs/git_branch.rs

@@ -9,6 +9,7 @@ pub struct GitBranchConfig<'a> {
     pub style: &'a str,
     pub truncation_length: i64,
     pub truncation_symbol: &'a str,
+    pub only_attached: bool,
     pub disabled: bool,
 }
 
@@ -20,6 +21,7 @@ impl<'a> RootModuleConfig<'a> for GitBranchConfig<'a> {
             style: "bold purple",
             truncation_length: std::i64::MAX,
             truncation_symbol: "…",
+            only_attached: false,
             disabled: false,
         }
     }

src/modules/git_branch.rs

@@ -1,6 +1,7 @@
 use unicode_segmentation::UnicodeSegmentation;
 
 use super::{Context, Module, RootModuleConfig};
+use git2::Repository;
 
 use crate::configs::git_branch::GitBranchConfig;
 use crate::formatter::StringFormatter;
@@ -25,6 +26,14 @@ pub fn module<'a>(context: &'a Context) -> Option<Module<'a>> {
     };
 
     let repo = context.get_repo().ok()?;
+
+    let repo_root = repo.root.as_ref()?;
+    let git_repo = Repository::open(repo_root).ok()?;
+    let is_detached = git_repo.head_detached().ok()?;
+    if config.only_attached && is_detached {
+        return None;
+    };
+
     let branch_name = repo.branch.as_ref()?;
 
     let mut graphemes: Vec<&str> = branch_name.graphemes(true).collect();
@@ -246,6 +255,57 @@ mod tests {
         repo_dir.close()
     }
 
+    #[test]
+    fn test_render_branch_only_attached_on_branch() -> io::Result<()> {
+        let repo_dir = fixture_repo(FixtureProvider::GIT)?;
+
+        Command::new("git")
+            .args(&["checkout", "-b", "test_branch"])
+            .current_dir(repo_dir.path())
+            .output()?;
+
+        let actual = ModuleRenderer::new("git_branch")
+            .config(toml::toml! {
+                [git_branch]
+                    only_attached = true
+            })
+            .path(&repo_dir.path())
+            .collect();
+
+        let expected = Some(format!(
+            "on {} ",
+            Color::Purple
+                .bold()
+                .paint(format!("\u{e0a0} {}", "test_branch")),
+        ));
+
+        assert_eq!(expected, actual);
+        repo_dir.close()
+    }
+
+    #[test]
+    fn test_render_branch_only_attached_on_detached() -> io::Result<()> {
+        let repo_dir = fixture_repo(FixtureProvider::GIT)?;
+
+        Command::new("git")
+            .args(&["checkout", "@~1"])
+            .current_dir(&repo_dir.path())
+            .output()?;
+
+        let actual = ModuleRenderer::new("git_branch")
+            .config(toml::toml! {
+                [git_branch]
+                    only_attached = true
+            })
+            .path(&repo_dir.path())
+            .collect();
+
+        let expected = None;
+
+        assert_eq!(expected, actual);
+        repo_dir.close()
+    }
+
     // This test is not possible until we switch to `git status --porcelain`
     // where we can mock the env for the specific git process. This is because
     // git2 does not care about our mocking and when we set the real `GIT_DIR`