Parse GIT_CONFIG_PARAMETERS

When git is invoked as `git -c aaa.bbb=ccc -c ddd.eee=fff` then git
sets the env var GIT_CONFIG_PARAMETERS containing the changed config
entries, so that child processes can honor them.

libgit2 doesn't yet honor the env var: see
https://github.com/libgit2/libgit2/issues/3854.

Fixes #493
Fixes #307
Ref https://github.com/dandavison/magit-delta/issues/13

2 files changed, 261 insertions, 5 deletions

diff --git a/src/git_config/git_config.rs b/src/git_config/git_config.rs
index ab831b31..96209603 100644
--- a/src/git_config/git_config.rs
+++ b/src/git_config/git_config.rs
@@ -1,9 +1,15 @@
+use regex::Regex;
+use std::collections::HashMap;
+use std::env;
 #[cfg(test)]
 use std::path::Path;
 use std::process;
 
+use lazy_static::lazy_static;
+
 pub struct GitConfig {
     config: git2::Config,
+    config_from_env_var: HashMap<String, String>,
     pub enabled: bool,
     pub repo: Option<git2::Repository>,
 }
@@ -26,6 +32,7 @@ impl GitConfig {
                 });
                 Some(Self {
                     config,
+                    config_from_env_var: parse_config_from_env_var(),
                     repo,
                     enabled: true,
                 })
@@ -38,6 +45,7 @@ impl GitConfig {
     pub fn from_path(path: &Path) -> Self {
         Self {
             config: git2::Config::open(path).unwrap(),
+            config_from_env_var: parse_config_from_env_var(),
             repo: None,
             enabled: true,
         }
@@ -55,6 +63,26 @@ impl GitConfig {
     }
 }
 
+fn parse_config_from_env_var() -> HashMap<String, String> {
+    if let Ok(s) = env::var("GIT_CONFIG_PARAMETERS") {
+        parse_config_from_env_var_value(&s)
+    } else {
+        HashMap::new()
+    }
+}
+
+lazy_static! {
+    static ref GIT_CONFIG_PARAMETERS_REGEX: Regex =
+        Regex::new(r"'(delta\.[a-z-]+)=([^']+)'").unwrap();
+}
+
+fn parse_config_from_env_var_value(s: &str) -> HashMap<String, String> {
+    GIT_CONFIG_PARAMETERS_REGEX
+        .captures_iter(s)
+        .map(|captures| (captures[1].to_string(), captures[2].to_string()))
+        .collect()
+}
+
 pub trait GitConfigGet {
     fn git_config_get(key: &str, git_config: &GitConfig) -> Option<Self>
     where
@@ -63,27 +91,42 @@ pub trait GitConfigGet {
 
 impl GitConfigGet for String {
     fn git_config_get(key: &str, git_config: &GitConfig) -> Option<Self> {
-        git_config.config.get_string(key).ok()
+        match git_config.config_from_env_var.get(key) {
+            Some(val) => Some(val.to_string()),
+            None => git_config.config.get_string(key).ok(),
+        }
     }
 }
 
 impl GitConfigGet for Option<String> {
     fn git_config_get(key: &str, git_config: &GitConfig) -> Option<Self> {
-        match git_config.config.get_string(key) {
-            Ok(value) => Some(Some(value)),
-            _ => None,
+        match git_config.config_from_env_var.get(key) {
+            Some(val) => Some(Some(val.to_string())),
+            None => match git_config.config.get_string(key) {
+                Ok(val) => Some(Some(val)),
+                _ => None,
+            },
         }
     }
 }
 
 impl GitConfigGet for bool {
     fn git_config_get(key: &str, git_config: &GitConfig) -> Option<Self> {
-        git_config.config.get_bool(key).ok()
+        match git_config.config_from_env_var.get(key).map(|s| s.as_str()) {
+            Some("true") => Some(true),
+            Some("false") => Some(false),
+            _ => git_config.config.get_bool(key).ok(),
+        }
     }
 }
 
 impl GitConfigGet for usize {
     fn git_config_get(key: &str, git_config: &GitConfig) -> Option<Self> {
+        if let Some(s) = git_config.config_from_env_var.get(key) {
+            if let Ok(n) = s.parse::<usize>() {
+                return Some(n);
+            }
+        }
         match git_config.config.get_i64(key) {
             Ok(value) => Some(value as usize),
             _ => None,
@@ -93,9 +136,55 @@ impl GitConfigGet for usize {
 
 impl GitConfigGet for f64 {
     fn git_config_get(key: &str, git_config: &GitConfig) -> Option<Self> {
+        if let Some(s) = git_config.config_from_env_var.get(key) {
+            if let Ok(n) = s.parse::<f64>() {
+                return Some(n);
+            }
+        }
         match git_config.config.get_string(key) {
             Ok(value) => value.parse::<f64>().ok(),
             _ => None,
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+
+    use super::parse_config_from_env_var_value;
+
+    #[test]
+    fn test_parse_config_from_env_var_value() {
+        // To generate test cases, use git -c ... with
+        // [core]
+        //     pager = env | grep GIT_CONFIG_PARAMETERS
+
+        let config = parse_config_from_env_var_value("'user.name=xxx'");
+        assert!(config.is_empty());
+
+        let config = parse_config_from_env_var_value("'delta.plus-style=green'");
+        assert_eq!(config["delta.plus-style"], "green");
+
+        let config = parse_config_from_env_var_value(
+            r##"'user.name=xxx' 'delta.hunk-header-line-number-style=red "#067a00"'"##,
+        );
+        assert_eq!(
+            config["delta.hunk-header-line-number-style"],
+            r##"red "#067a00""##
+        );
+
+        let config =
+            parse_config_from_env_var_value(r##"'user.name=xxx' 'delta.side-by-side=false'"##);
+        assert_eq!(config["delta.side-by-side"], "false");
+
+        let config = parse_config_from_env_var_value(
+            r##"'delta.plus-style=green' 'delta.side-by-side=false' 'delta.hunk-header-line-number-style=red "#067a00"'"##,
+        );
+        assert_eq!(config["delta.plus-style"], "green");
+        assert_eq!(config["delta.side-by-side"], "false");
+        assert_eq!(
+            config["delta.hunk-header-line-number-style"],
+            r##"red "#067a00""##
+        );
+    }
+}
diff --git a/src/options/get.rs b/src/options/get.rs
index e29b8cdf..f19c3293 100644
--- a/src/options/get.rs
+++ b/src/options/get.rs
@@ -109,3 +109,170 @@ impl GetOptionValue for String {}
 impl GetOptionValue for bool {}
 impl GetOptionValue for f64 {}
 impl GetOptionValue for usize {}
+
+#[cfg(test)]
+pub mod tests {
+    use std::env;
+    use std::fs::remove_file;
+
+    use crate::tests::integration_test_utils::integration_test_utils;
+
+    #[test]
+    fn test_simple_string_env_var_overrides_git_config() {
+        let git_config_contents = b"
+[delta]
+    plus-style = blue
+";
+        let git_config_path = "delta__test_simple_string_env_var_overrides_git_config.gitconfig";
+
+        let opt = integration_test_utils::make_options_from_args_and_git_config(
+            &[],
+            Some(git_config_contents),
+            Some(git_config_path),
+        );
+        assert_eq!(opt.plus_style, "blue");
+
+        env::set_var("GIT_CONFIG_PARAMETERS", "'delta.plus-style=green'");
+        let opt = integration_test_utils::make_options_from_args_and_git_config(
+            &[],
+            Some(git_config_contents),
+            Some(git_config_path),
+        );
+        assert_eq!(opt.plus_style, "green");
+
+        remove_file(git_config_path).unwrap();
+    }
+
+    #[test]
+    fn test_complex_string_env_var_overrides_git_config() {
+        let git_config_contents = br##"
+[delta]
+    minus-style = red bold ul "#ffeeee"
+"##;
+        let git_config_path = "delta__test_complex_string_env_var_overrides_git_config.gitconfig";
+
+        let opt = integration_test_utils::make_options_from_args_and_git_config(
+            &[],
+            Some(git_config_contents),
+            Some(git_config_path),
+        );
+        assert_eq!(opt.minus_style, r##"red bold ul #ffeeee"##);
+
+        env::set_var(
+            "GIT_CONFIG_PARAMETERS",
+            r##"'delta.minus-style=magenta italic ol "#aabbcc"'"##,
+        );
+        let opt = integration_test_utils::make_options_from_args_and_git_config(
+            &[],
+            Some(git_config_contents),
+            Some(git_config_path),
+        );
+        assert_eq!(opt.minus_style, r##"magenta italic ol "#aabbcc""##,);
+
+        remove_file(git_config_path).unwrap();
+    }
+
+    #[test]
+    fn test_option_string_env_var_overrides_git_config() {
+        let git_config_contents = b"
+[delta]
+    plus-style = blue
+";
+        let git_config_path = "delta__test_option_string_env_var_overrides_git_config.gitconfig";
+
+        let opt = integration_test_utils::make_options_from_args_and_git_config(
+            &[],
+            Some(git_config_contents),
+            Some(git_config_path),
+        );
+        assert_eq!(opt.plus_style, "blue");
+
+        env::set_var("GIT_CONFIG_PARAMETERS", "'delta.plus-style=green'");
+        let opt = integration_test_utils::make_options_from_args_and_git_config(
+            &[],
+            Some(git_config_contents),
+            Some(git_config_path),
+        );
+        assert_eq!(opt.plus_style, "green");
+
+        remove_file(git_config_path).unwrap();
+    }
+
+    #[test]
+    fn test_bool_env_var_overrides_git_config() {
+        let git_config_contents = b"
+[delta]
+    side-by-side = true
+";
+        let git_config_path = "delta__test_bool_env_var_overrides_git_config.gitconfig";
+
+        let opt = integration_test_utils::make_options_from_args_and_git_config(
+            &[],
+            Some(git_config_contents),
+            Some(git_config_path),
+        );
+        assert_eq!(opt.side_by_side, true);
+
+        env::set_var("GIT_CONFIG_PARAMETERS", "'delta.side-by-side=false'");
+        let opt = integration_test_utils::make_options_from_args_and_git_config(
+            &[],
+            Some(git_config_contents),
+            Some(git_config_path),
+        );
+        assert_eq!(opt.side_by_side, false);
+
+        remove_file(git_config_path).unwrap();
+    }
+
+    #[test]
+    fn test_int_env_var_overrides_git_config() {
+        let git_config_contents = b"
+[delta]
+    max-line-length = 1
+";
+        let git_config_path = "delta__test_int_env_var_overrides_git_config.gitconfig";
+
+        let opt = integration_test_utils::make_options_from_args_and_git_config(
+            &[],
+            Some(git_config_contents),
+            Some(git_config_path),
+        );
+        assert_eq!(opt.max_line_length, 1);
+
+        env::set_var("GIT_CONFIG_PARAMETERS", "'delta.max-line-length=2'");
+        let opt = integration_test_utils::make_options_from_args_and_git_config(
+            &[],
+            Some(git_config_contents),
+            Some(git_config_path),
+        );
+        assert_eq!(opt.max_line_length, 2);
+
+        remove_file(git_config_path).unwrap();
+    }
+
+    #[test]
+    fn test_float_env_var_overrides_git_config() {
+        let git_config_contents = b"
+[delta]
+    max-line-distance = 0.6
+";
+        let git_config_path = "delta__test_float_env_var_overrides_git_config.gitconfig";
+
+        let opt = integration_test_utils::make_options_from_args_and_git_config(
+            &[],
+            Some(git_config_contents),
+            Some(git_config_path),
+        );
+        assert_eq!(opt.max_line_distance, 0.6);
+
+        env::set_var("GIT_CONFIG_PARAMETERS", "'delta.max-line-distance=0.7'");
+        let opt = integration_test_utils::make_options_from_args_and_git_config(
+            &[],
+            Some(git_config_contents),
+            Some(git_config_path),
+        );
+        assert_eq!(opt.max_line_distance, 0.7);
+
+        remove_file(git_config_path).unwrap();
+    }
+}