feat(fossil_metrics): add fossil_metrics module (#4874)

* feat(fossil_metrics): add fossil_metrics module

* Return early if not in a Fossil check-out

* Add more tests for fossil_metrics

* Move is in Fossil checkout check after module enabled check

* Update type for new toml version

* Update the config file schema

* Rework parsing of fossil diff output

* Fix Fossil check-out detection in subdirectories

* Use regex to only match expected fossil diff output

* Use shared ancestor scanning and fix detection on Windows

* Add note on minimum Fossil version

2 files changed, 300 insertions, 0 deletions

diff --git a/src/modules/fossil_metrics.rs b/src/modules/fossil_metrics.rs
new file mode 100644
index 000000000..5ec97b6c1
--- /dev/null
+++ b/src/modules/fossil_metrics.rs
@@ -0,0 +1,297 @@
+use regex::Regex;
+
+use super::{Context, Module, ModuleConfig};
+
+use crate::configs::fossil_metrics::FossilMetricsConfig;
+use crate::formatter::StringFormatter;
+
+/// Creates a module with currently added/deleted lines in the Fossil check-out in the current
+/// directory.
+pub fn module<'a>(context: &'a Context) -> Option<Module<'a>> {
+    let mut module = context.new_module("fossil_metrics");
+    let config = FossilMetricsConfig::try_load(module.config);
+
+    // As we default to disabled=true, we have to check here after loading our config module,
+    // before it was only checking against whatever is in the config starship.toml
+    if config.disabled {
+        return None;
+    };
+
+    let checkout_db = if cfg!(windows) {
+        "_FOSSIL_"
+    } else {
+        ".fslckout"
+    };
+    // See if we're in a check-out by scanning upwards for a directory containing the checkout_db file
+    context
+        .begin_ancestor_scan()
+        .set_files(&[checkout_db])
+        .scan()?;
+
+    // Read the total number of added and deleted lines from "fossil diff --numstat"
+    let output = context.exec_cmd("fossil", &["diff", "--numstat"])?.stdout;
+    let stats = FossilDiff::parse(&output, config.only_nonzero_diffs);
+
+    let parsed = StringFormatter::new(config.format).and_then(|formatter| {
+        formatter
+            .map_style(|variable| match variable {
+                "added_style" => Some(Ok(config.added_style)),
+                "deleted_style" => Some(Ok(config.deleted_style)),
+                _ => None,
+            })
+            .map(|variable| match variable {
+                "added" => Some(Ok(stats.added)),
+                "deleted" => Some(Ok(stats.deleted)),
+                _ => None,
+            })
+            .parse(None, Some(context))
+    });
+
+    module.set_segments(match parsed {
+        Ok(segments) => segments,
+        Err(error) => {
+            log::warn!("Error in module `fossil_metrics`:\n{}", error);
+            return None;
+        }
+    });
+
+    Some(module)
+}
+
+/// Represents the parsed output from a Fossil diff with the --numstat option enabled.
+#[derive(Debug, PartialEq)]
+struct FossilDiff<'a> {
+    added: &'a str,
+    deleted: &'a str,
+}
+
+impl<'a> FossilDiff<'a> {
+    /// Parses the output of `fossil diff --numstat` as a `FossilDiff` struct.
+    pub fn parse(diff_numstat: &'a str, only_nonzero_diffs: bool) -> Self {
+        // Fossil formats the last line of the output as "%10d %10d TOTAL over %d changed files\n"
+        // where the 1st and 2nd placeholders are the number of added and deleted lines respectively
+        let re = Regex::new(r"^\s*(\d+)\s+(\d+) TOTAL over \d+ changed files$").unwrap();
+
+        let (added, deleted) = diff_numstat
+            .lines()
+            .last()
+            .and_then(|s| re.captures(s))
+            .and_then(|caps| {
+                let added = match caps.get(1)?.as_str() {
+                    "0" if only_nonzero_diffs => "",
+                    s => s,
+                };
+
+                let deleted = match caps.get(2)?.as_str() {
+                    "0" if only_nonzero_diffs => "",
+                    s => s,
+                };
+
+                Some((added, deleted))
+            })
+            .unwrap_or_default();
+
+        Self { added, deleted }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::io;
+    use std::path::Path;
+
+    use nu_ansi_term::{Color, Style};
+
+    use crate::test::{fixture_repo, FixtureProvider, ModuleRenderer};
+
+    use super::FossilDiff;
+
+    enum Expect<'a> {
+        Empty,
+        Added(Option<&'a str>),
+        AddedStyle(Style),
+        Deleted(Option<&'a str>),
+        DeletedStyle(Style),
+    }
+
+    #[test]
+    fn show_nothing_on_empty_dir() -> io::Result<()> {
+        let checkout_dir = tempfile::tempdir()?;
+
+        let actual = ModuleRenderer::new("fossil_metrics")
+            .path(checkout_dir.path())
+            .collect();
+        let expected = None;
+        assert_eq!(expected, actual);
+
+        checkout_dir.close()
+    }
+
+    #[test]
+    fn test_fossil_metrics_disabled_per_default() -> io::Result<()> {
+        let tempdir = fixture_repo(FixtureProvider::Fossil)?;
+        let checkout_dir = tempdir.path();
+        expect_fossil_metrics_with_config(
+            checkout_dir,
+            Some(toml::toml! {
+                // no "disabled=false" in config!
+                [fossil_metrics]
+                only_nonzero_diffs = false
+            }),
+            &[Expect::Empty],
+        );
+        tempdir.close()
+    }
+
+    #[test]
+    fn test_fossil_metrics_autodisabled() -> io::Result<()> {
+        let tempdir = tempfile::tempdir()?;
+        expect_fossil_metrics_with_config(tempdir.path(), None, &[Expect::Empty]);
+        tempdir.close()
+    }
+
+    #[test]
+    fn test_fossil_metrics() -> io::Result<()> {
+        let tempdir = fixture_repo(FixtureProvider::Fossil)?;
+        let checkout_dir = tempdir.path();
+        expect_fossil_metrics_with_config(
+            checkout_dir,
+            None,
+            &[Expect::Added(Some("3")), Expect::Deleted(Some("2"))],
+        );
+        tempdir.close()
+    }
+
+    #[test]
+    fn test_fossil_metrics_subdir() -> io::Result<()> {
+        let tempdir = fixture_repo(FixtureProvider::Fossil)?;
+        let checkout_dir = tempdir.path();
+        expect_fossil_metrics_with_config(
+            &checkout_dir.join("subdir"),
+            None,
+            &[Expect::Added(Some("3")), Expect::Deleted(Some("2"))],
+        );
+        tempdir.close()
+    }
+
+    #[test]
+    fn test_fossil_metrics_configured() -> io::Result<()> {
+        let tempdir = fixture_repo(FixtureProvider::Fossil)?;
+        let checkout_dir = tempdir.path();
+        expect_fossil_metrics_with_config(
+            checkout_dir,
+            Some(toml::toml! {
+                [fossil_metrics]
+                added_style = "underline blue"
+                deleted_style = "underline purple"
+                disabled = false
+            }),
+            &[
+                Expect::Added(Some("3")),
+                Expect::AddedStyle(Color::Blue.underline()),
+                Expect::Deleted(Some("2")),
+                Expect::DeletedStyle(Color::Purple.underline()),
+            ],
+        );
+        tempdir.close()
+    }
+
+    #[test]
+    fn parse_no_changes_discard_zeros() {
+        let actual = FossilDiff::parse("         0          0 TOTAL over 0 changed files\n", true);
+        let expected = FossilDiff {
+            added: "",
+            deleted: "",
+        };
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn parse_no_changes_keep_zeros() {
+        let actual = FossilDiff::parse("         0          0 TOTAL over 0 changed files\n", false);
+        let expected = FossilDiff {
+            added: "0",
+            deleted: "0",
+        };
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn parse_with_changes() {
+        let actual = FossilDiff::parse(
+            "         3          2 README.md\n         3          2 TOTAL over 1 changed files\n",
+            true,
+        );
+        let expected = FossilDiff {
+            added: "3",
+            deleted: "2",
+        };
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn parse_ignore_empty() {
+        let actual = FossilDiff::parse("", true);
+        let expected = FossilDiff {
+            added: "",
+            deleted: "",
+        };
+        assert_eq!(expected, actual);
+    }
+
+    /// Tests output as produced by Fossil v2.3 to v2.14, i.e. without the summary line.
+    #[test]
+    fn parse_ignore_when_missing_total_line() {
+        let actual = FossilDiff::parse("         3          2 README.md\n", true);
+        let expected = FossilDiff {
+            added: "",
+            deleted: "",
+        };
+        assert_eq!(expected, actual);
+    }
+
+    fn expect_fossil_metrics_with_config(
+        checkout_dir: &Path,
+        config: Option<toml::Table>,
+        expectations: &[Expect],
+    ) {
+        let actual = ModuleRenderer::new("fossil_metrics")
+            .path(checkout_dir.to_str().unwrap())
+            .config(config.unwrap_or_else(|| {
+                toml::toml! {
+                    [fossil_metrics]
+                    disabled = false
+                }
+            }))
+            .collect();
+
+        let mut expect_added = Some("3");
+        let mut expect_added_style = Color::Green.bold();
+        let mut expect_deleted = Some("2");
+        let mut expect_deleted_style = Color::Red.bold();
+
+        for expect in expectations {
+            match expect {
+                Expect::Empty => {
+                    assert_eq!(None, actual);
+                    return;
+                }
+                Expect::Added(added) => expect_added = *added,
+                Expect::AddedStyle(style) => expect_added_style = *style,
+                Expect::Deleted(deleted) => expect_deleted = *deleted,
+                Expect::DeletedStyle(style) => expect_deleted_style = *style,
+            }
+        }
+
+        let expected = Some(format!(
+            "{}{}",
+            expect_added
+                .map(|added| format!("{} ", expect_added_style.paint(format!("+{added}"))))
+                .unwrap_or(String::from("")),
+            expect_deleted
+                .map(|deleted| format!("{} ", expect_deleted_style.paint(format!("-{deleted}"))))
+                .unwrap_or(String::from("")),
+        ));
+        assert_eq!(expected, actual);
+    }
+}
diff --git a/src/modules/mod.rs b/src/modules/mod.rs
index d60cdc50f..fe4f42305 100644
--- a/src/modules/mod.rs
+++ b/src/modules/mod.rs
@@ -25,6 +25,7 @@ mod erlang;
 mod fennel;
 mod fill;
 mod fossil_branch;
+mod fossil_metrics;
 mod gcloud;
 mod git_branch;
 mod git_commit;
@@ -129,6 +130,7 @@ pub fn handle<'a>(module: &str, context: &'a Context) -> Option<Module<'a>> {
             "fennel" => fennel::module(context),
             "fill" => fill::module(context),
             "fossil_branch" => fossil_branch::module(context),
+            "fossil_metrics" => fossil_metrics::module(context),
             "gcloud" => gcloud::module(context),
             "git_branch" => git_branch::module(context),
             "git_commit" => git_commit::module(context),
@@ -244,6 +246,7 @@ pub fn description(module: &str) -> &'static str {
         "fennel" => "The currently installed version of Fennel",
         "fill" => "Fills the remaining space on the line with a pad string",
         "fossil_branch" => "The active branch of the check-out in your current directory",
+        "fossil_metrics" => "The currently added/deleted lines in your check-out",
         "gcloud" => "The current GCP client configuration",
         "git_branch" => "The active branch of the repo in your current directory",
         "git_commit" => "The active commit (and tag if any) of the repo in your current directory",