report which lines changed on up/down

set_local_db, toggle_after_line and set_dot_env now return a
FileChange (path + before/after line pairs) instead of (), and main
prints it after each toggle so 'up'/'down' shows exactly what the
program rewrote in each env file.

src/config/parse.rs

@@ -1,4 +1,5 @@
 use std::{
+    fmt,
     fs::{self, File},
     io::{BufRead, BufReader},
 };
@@ -9,8 +10,27 @@ use crate::env::config::DevToolsConf;
 pub const GLOBAL_CONNECTION_PATH: &str = "conf/global/connections.env";
 const LOCAL_CONNECTION_PATH: &str = "conf/local/.env";
 
+/// The lines a toggle operation rewrote in a given file, as (before, after) pairs.
+pub struct FileChange {
+    pub path: String,
+    pub diffs: Vec<(String, String)>,
+}
+
+impl fmt::Display for FileChange {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if self.diffs.is_empty() {
+            return writeln!(f, "[!] {}: no changes", self.path);
+        }
+        writeln!(f, "[!] {} changed:", self.path)?;
+        for (before, after) in &self.diffs {
+            writeln!(f, "    {} -> {}", before, after)?;
+        }
+        Ok(())
+    }
+}
+
 /// writes global connections
-pub fn set_local_db(start: bool, config: &DevToolsConf) -> Result<()> {
+pub fn set_local_db(start: bool, config: &DevToolsConf) -> Result<FileChange> {
     let global_connections_env = format!(
         "{}{}",
         config.project_dir_as_string(),
@@ -21,27 +41,39 @@ pub fn set_local_db(start: bool, config: &DevToolsConf) -> Result<()> {
     let reader: BufReader<File> = BufReader::new(file);
 
     let mut modified_lines: Vec<String> = Vec::new();
+    let mut diffs: Vec<(String, String)> = Vec::new();
     for line in reader.lines() {
         let line_content = line?;
-        let modified = if start && connections_env_comment(&line_content) {
+        let modified: Option<String> = if start && connections_env_comment(&line_content) {
-            format!("# {}", line_content)
+            Some(format!("# {}", line_content))
         } else if !start && should_commented_out(&line_content) {
-            line_content[2..].to_string()
+            Some(line_content[2..].to_string())
         } else {
-            line_content
+            None
         };
-        modified_lines.push(modified);
+
+        match modified {
+            Some(new_line) => {
+                diffs.push((line_content, new_line.clone()));
+                modified_lines.push(new_line);
+            }
+            None => modified_lines.push(line_content),
+        }
     }
 
-    fs::write(global_connections_env, modified_lines.join("\n"))
+    fs::write(&global_connections_env, modified_lines.join("\n"))
         .context("Cannot write global connections env")?;
-    Ok(())
+    Ok(FileChange {
+        path: global_connections_env,
+        diffs,
+    })
 }
 
-pub fn set_dot_env(start: bool, config: &DevToolsConf) -> Result<()> {
+pub fn set_dot_env(start: bool, config: &DevToolsConf) -> Result<FileChange> {
-    toggle_after_line("#docker", 4, start, config)?;
+    let mut docker_change = toggle_after_line("#docker", 4, start, config)?;
-    toggle_after_line("#cidb", 2, !start, config)?;
+    let cidb_change = toggle_after_line("#cidb", 2, !start, config)?;
-    Ok(())
+    docker_change.diffs.extend(cidb_change.diffs);
+    Ok(docker_change)
 }
 
 const CI_DB_MASTER_IP: &str = "ci.db.master.ip";
@@ -85,7 +117,7 @@ fn toggle_after_line(
     num_lines: usize,
     activate: bool,
     config: &DevToolsConf,
-) -> Result<()> {
+) -> Result<FileChange> {
     let local_connection_env = format!(
         "{}{}",
         config.project_dir_as_string(),
@@ -96,6 +128,7 @@ fn toggle_after_line(
     let reader: BufReader<File> = BufReader::new(file);
 
     let mut modified_lines: Vec<String> = Vec::new();
+    let mut diffs: Vec<(String, String)> = Vec::new();
     let mut relevant = false;
     let mut counter: usize = 0;
 
@@ -111,21 +144,34 @@ fn toggle_after_line(
             continue;
         }
 
-        if relevant {
+        let modified: Option<String> = if relevant {
-            modified_lines.push(toggle(&line_content, activate));
             counter += 1;
+            let new_line = toggle(&line_content, activate);
+            (new_line != line_content).then_some(new_line)
         } else if let Some(key) = connection_key(&line_content) {
             let value = if activate { "staging" } else { "ci" };
-            modified_lines.push(format!("{}='{}'", key, value));
+            let new_line = format!("{}='{}'", key, value);
+            (new_line != line_content).then_some(new_line)
         } else {
-            modified_lines.push(line_content);
+            None
+        };
+
+        match modified {
+            Some(new_line) => {
+                diffs.push((line_content, new_line.clone()));
+                modified_lines.push(new_line);
+            }
+            None => modified_lines.push(line_content),
         }
     }
 
-    fs::write(local_connection_env, modified_lines.join("\n"))
+    fs::write(&local_connection_env, modified_lines.join("\n"))
         .context("Cannot write local connection env")?;
 
-    Ok(())
+    Ok(FileChange {
+        path: local_connection_env,
+        diffs,
+    })
 }
 
 /// Returns the `connection` key as it appears on the given line (either the
@@ -156,6 +202,228 @@ pub(crate) fn toggle(line: &str, activate: bool) -> String {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use std::ops::Deref;
+    use std::path::{Path, PathBuf};
+
+    /// An isolated `conf/global`/`conf/local` tree under the OS temp dir, for
+    /// exercising `set_local_db`/`set_dot_env` against real files without
+    /// touching this repo's own `conf/` directory. Namespaced by process id
+    /// so concurrent `cargo test` runs can't collide on the same path, and
+    /// removed on drop so no stale directories accumulate.
+    struct TempProjectDir(PathBuf);
+
+    impl TempProjectDir {
+        fn new(name: &str) -> Self {
+            let dir = std::env::temp_dir().join(format!(
+                "dev_tools_parse_test_{}_{}",
+                std::process::id(),
+                name
+            ));
+            let _ = fs::remove_dir_all(&dir);
+            fs::create_dir_all(dir.join("conf/global")).unwrap();
+            fs::create_dir_all(dir.join("conf/local")).unwrap();
+            Self(dir)
+        }
+    }
+
+    impl Deref for TempProjectDir {
+        type Target = Path;
+        fn deref(&self) -> &Path {
+            &self.0
+        }
+    }
+
+    impl Drop for TempProjectDir {
+        fn drop(&mut self) {
+            let _ = fs::remove_dir_all(&self.0);
+        }
+    }
+
+    fn config_for(dir: &Path) -> DevToolsConf {
+        DevToolsConf {
+            container_service: String::new(),
+            container_dir: String::new(),
+            project_directory: PathBuf::from(format!("{}/", dir.display())),
+        }
+    }
+
+    #[test]
+    fn set_local_db_records_diffs_when_commenting_out() {
+        let dir = TempProjectDir::new("comment_out");
+        fs::write(
+            dir.join(GLOBAL_CONNECTION_PATH),
+            "ci.db.master.ip=127.0.0.1\nci.db.master.port=5432\nci.db.master.user=admin\nRCC_CI_DB_MASTER_IP=127.0.0.1",
+        )
+        .unwrap();
+
+        let change = set_local_db(true, &config_for(&dir)).unwrap();
+
+        assert_eq!(
+            change.diffs,
+            vec![
+                (
+                    "ci.db.master.ip=127.0.0.1".to_string(),
+                    "# ci.db.master.ip=127.0.0.1".to_string()
+                ),
+                (
+                    "ci.db.master.port=5432".to_string(),
+                    "# ci.db.master.port=5432".to_string()
+                ),
+                (
+                    "RCC_CI_DB_MASTER_IP=127.0.0.1".to_string(),
+                    "# RCC_CI_DB_MASTER_IP=127.0.0.1".to_string()
+                ),
+            ]
+        );
+    }
+
+    #[test]
+    fn set_local_db_records_diffs_when_uncommenting() {
+        let dir = TempProjectDir::new("uncomment");
+        fs::write(
+            dir.join(GLOBAL_CONNECTION_PATH),
+            "# ci.db.master.ip=127.0.0.1\n# ci.db.master.port=5432\nci.db.master.user=admin",
+        )
+        .unwrap();
+
+        let change = set_local_db(false, &config_for(&dir)).unwrap();
+
+        assert_eq!(
+            change.diffs,
+            vec![
+                (
+                    "# ci.db.master.ip=127.0.0.1".to_string(),
+                    "ci.db.master.ip=127.0.0.1".to_string()
+                ),
+                (
+                    "# ci.db.master.port=5432".to_string(),
+                    "ci.db.master.port=5432".to_string()
+                ),
+            ]
+        );
+    }
+
+    #[test]
+    fn toggle_after_line_records_diffs_for_toggled_section() {
+        let dir = TempProjectDir::new("toggle_section");
+        fs::write(
+            dir.join(LOCAL_CONNECTION_PATH),
+            "#docker\nDOCKER_HOST=tcp://localhost:2375\n#DOCKER_TLS_VERIFY=1\n#DOCKER_CERT_PATH=/certs\nDOCKER_API_VERSION=1.41\nother=1",
+        )
+        .unwrap();
+
+        let change = toggle_after_line("#docker", 4, true, &config_for(&dir)).unwrap();
+
+        assert_eq!(
+            change.diffs,
+            vec![
+                (
+                    "#DOCKER_TLS_VERIFY=1".to_string(),
+                    "DOCKER_TLS_VERIFY=1".to_string()
+                ),
+                (
+                    "#DOCKER_CERT_PATH=/certs".to_string(),
+                    "DOCKER_CERT_PATH=/certs".to_string()
+                ),
+            ]
+        );
+    }
+
+    #[test]
+    fn toggle_after_line_records_diffs_for_both_connection_keys() {
+        let dir = TempProjectDir::new("connection_keys");
+        fs::write(
+            dir.join(LOCAL_CONNECTION_PATH),
+            "#docker\nline1\nline2\nline3\nline4\nconnection='staging'\nRCC_CONNECTION='staging'",
+        )
+        .unwrap();
+
+        let change = toggle_after_line("#cidb", 2, false, &config_for(&dir)).unwrap();
+
+        assert_eq!(
+            change.diffs,
+            vec![
+                (
+                    "connection='staging'".to_string(),
+                    "connection='ci'".to_string()
+                ),
+                (
+                    "RCC_CONNECTION='staging'".to_string(),
+                    "RCC_CONNECTION='ci'".to_string()
+                ),
+            ]
+        );
+    }
+
+    #[test]
+    fn set_dot_env_merges_diffs_from_both_sections() {
+        let dir = TempProjectDir::new("merge_sections");
+        fs::write(
+            dir.join(LOCAL_CONNECTION_PATH),
+            "#docker\nDOCKER_HOST=tcp://localhost:2375\n#DOCKER_TLS_VERIFY=1\n#DOCKER_CERT_PATH=/certs\nDOCKER_API_VERSION=1.41\n#cidb\nci.db.master.ip=127.0.0.1\nci.db.master.port=5432\nconnection='staging'\nRCC_CONNECTION='staging'",
+        )
+        .unwrap();
+
+        let change = set_dot_env(true, &config_for(&dir)).unwrap();
+
+        assert!(change.path.ends_with(LOCAL_CONNECTION_PATH));
+        assert_eq!(change.diffs.len(), 6);
+        for expected in [
+            ("#DOCKER_TLS_VERIFY=1", "DOCKER_TLS_VERIFY=1"),
+            ("#DOCKER_CERT_PATH=/certs", "DOCKER_CERT_PATH=/certs"),
+            ("ci.db.master.ip=127.0.0.1", "#ci.db.master.ip=127.0.0.1"),
+            ("ci.db.master.port=5432", "#ci.db.master.port=5432"),
+            ("connection='staging'", "connection='ci'"),
+            ("RCC_CONNECTION='staging'", "RCC_CONNECTION='ci'"),
+        ] {
+            assert!(
+                change
+                    .diffs
+                    .contains(&(expected.0.to_string(), expected.1.to_string())),
+                "missing diff {:?}",
+                expected
+            );
+        }
+    }
+
+    #[test]
+    fn file_change_display_no_diffs() {
+        let change = FileChange {
+            path: "some/path".to_string(),
+            diffs: vec![],
+        };
+        assert_eq!(format!("{}", change), "[!] some/path: no changes\n");
+    }
+
+    #[test]
+    fn file_change_display_with_diffs() {
+        let change = FileChange {
+            path: "some/path".to_string(),
+            diffs: vec![(
+                "connection='ci'".to_string(),
+                "connection='staging'".to_string(),
+            )],
+        };
+        assert_eq!(
+            format!("{}", change),
+            "[!] some/path changed:\n    connection='ci' -> connection='staging'\n"
+        );
+    }
+
+    #[test]
+    fn file_change_display_with_multiple_diffs() {
+        let change = FileChange {
+            path: "some/path".to_string(),
+            diffs: vec![
+                ("a=1".to_string(), "#a=1".to_string()),
+                ("b=2".to_string(), "#b=2".to_string()),
+            ],
+        };
+        assert_eq!(
+            format!("{}", change),
+            "[!] some/path changed:\n    a=1 -> #a=1\n    b=2 -> #b=2\n"
+        );
+    }
 
     #[test]
     fn toggle_activate_removes_leading_hash() {

src/main.rs

@@ -24,13 +24,13 @@ fn main() -> Result<()> {
     start_docker_compose(&config.container_service, &config.container_dir, start)?;
     if args.legacy {
         println!("[!] Legacy mode active.");
-        set_local_db(start, &config)?;
+        print!("{}", set_local_db(start, &config)?);
         toggle_index(start, &config)?;
     } else {
         println!("[!] Legacy mode deactivated.");
     }
 
-    set_dot_env(start, &config)?;
+    print!("{}", set_dot_env(start, &config)?);
 
     println!(
         "[!] Don't forget your interpreter! Project directory: {}",