Clarify git credential code and fix infinite loop bug (#898)

Fixes #897

crates/bin/src/git_credentials.rs

@@ -0,0 +1,67 @@
+use std::{
+    env, fs,
+    path::{Path, PathBuf},
+};
+
+use compact_str::CompactString;
+use dirs::home_dir;
+
+pub fn try_from_home() -> Option<CompactString> {
+    if let Some(mut home) = home_dir() {
+        home.push(".git-credentials");
+        if let Some(cred) = from_file(home) {
+            return Some(cred);
+        }
+    }
+
+    if let Some(home) = env::var_os("XDG_CONFIG_HOME") {
+        let home = Path::new(&home).join("git/credentials");
+        if let Some(cred) = from_file(home) {
+            return Some(cred);
+        }
+    }
+
+    None
+}
+
+fn from_file(path: PathBuf) -> Option<CompactString> {
+    fs::read_to_string(path)
+        .ok()?
+        .lines()
+        .find_map(from_line)
+        .map(CompactString::from)
+}
+
+fn from_line(line: &str) -> Option<&str> {
+    let cred = line
+        .trim()
+        .strip_prefix("https://")?
+        .strip_suffix("@github.com")?;
+
+    Some(cred.split_once(':')?.1)
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    const GIT_CREDENTIALS_TEST_CASES: &[(&str, Option<&str>)] = &[
+        // Success
+        ("https://NobodyXu:gho_asdc@github.com", Some("gho_asdc")),
+        (
+            "https://NobodyXu:gho_asdc12dz@github.com",
+            Some("gho_asdc12dz"),
+        ),
+        // Failure
+        ("http://NobodyXu:gho_asdc@github.com", None),
+        ("https://NobodyXu:gho_asdc@gitlab.com", None),
+        ("https://NobodyXugho_asdc@github.com", None),
+    ];
+
+    #[test]
+    fn test_extract_from_line() {
+        GIT_CREDENTIALS_TEST_CASES.iter().for_each(|(line, res)| {
+            assert_eq!(from_line(line), *res);
+        })
+    }
+}