Implement path expansion support for theme-directory configuration

README.md

@@ -89,6 +89,19 @@ git config split-diffs.min-line-width 40
 
 This defaults to `80`, so screens below `160` characters will display unified diffs. Set it to `0` to always show split diffs.
 
+### Custom theme directory
+
+You can specify a custom directory for themes using the `theme-directory` setting. This supports path expansion for convenient configuration:
+
+```
+git config split-diffs.theme-directory ~/my/themes/split-diff
+```
+
+The following expansions are supported:
+- `~` and `~/` expand to your home directory
+- `$HOME`, `${HOME}`, `$USER`, and other environment variables are expanded
+- Relative paths are resolved to absolute paths
+
 ## Themes
 
 You can pick between several [themes](themes/):

src/getGitConfig.test.ts

@@ -67,4 +67,105 @@ split-diffs.theme-name=baz
             THEME_NAME: 'baz',
         });
     });
+
+    describe('theme-directory path expansion', () => {
+        const originalEnv = process.env;
+
+        beforeEach(() => {
+            // Set up test environment variables
+            process.env = {
+                ...originalEnv,
+                TEST_HOME: '/home/testuser',
+                TEST_USER: 'testuser',
+                TEST_CUSTOM: 'custom_value',
+            };
+        });
+
+        afterEach(() => {
+            // Restore original environment
+            process.env = originalEnv;
+        });
+
+        test('expands $TEST_HOME environment variable', () => {
+            const result = getGitConfig(`
+split-diffs.theme-directory=$TEST_HOME/my/themes/split-diff
+            `);
+            expect(result.THEME_DIRECTORY).toBe('/home/testuser/my/themes/split-diff');
+        });
+
+        test('expands ${TEST_HOME} environment variable with braces', () => {
+            const result = getGitConfig(`
+split-diffs.theme-directory=\${TEST_HOME}/my/themes/split-diff
+            `);
+            expect(result.THEME_DIRECTORY).toBe('/home/testuser/my/themes/split-diff');
+        });
+
+        test('expands $TEST_USER environment variable in path', () => {
+            const result = getGitConfig(`
+split-diffs.theme-directory=/Users/$TEST_USER/my/themes/split-diff
+            `);
+            expect(result.THEME_DIRECTORY).toBe('/Users/testuser/my/themes/split-diff');
+        });
+
+        test('expands ${TEST_USER} environment variable with braces', () => {
+            const result = getGitConfig(`
+split-diffs.theme-directory=/Users/\${TEST_USER}/my/themes/split-diff
+            `);
+            expect(result.THEME_DIRECTORY).toBe('/Users/testuser/my/themes/split-diff');
+        });
+
+        test('expands multiple environment variables', () => {
+            const result = getGitConfig(`
+split-diffs.theme-directory=$TEST_HOME/\${TEST_USER}/themes/\${TEST_CUSTOM}
+            `);
+            expect(result.THEME_DIRECTORY).toBe('/home/testuser/testuser/themes/custom_value');
+        });
+
+        test('handles missing environment variables as empty string', () => {
+            const result = getGitConfig(`
+split-diffs.theme-directory=$TEST_HOME/\${NONEXISTENT}/themes
+            `);
+            expect(result.THEME_DIRECTORY).toBe('/home/testuser/themes');
+        });
+
+        test('returns absolute path for relative input', () => {
+            const result = getGitConfig(`
+split-diffs.theme-directory=./relative/path
+            `);
+            expect(result.THEME_DIRECTORY).toContain('/relative/path');
+            expect(result.THEME_DIRECTORY.startsWith('./')).toBe(false);
+        });
+
+        test('leaves absolute paths unchanged (except expansion)', () => {
+            const result = getGitConfig(`
+split-diffs.theme-directory=/absolute/path
+            `);
+            expect(result.THEME_DIRECTORY).toBe('/absolute/path');
+        });
+
+        test('does not expand when theme-directory is not set', () => {
+            const result = getGitConfig(`
+split-diffs.theme-name=arctic
+            `);
+            expect(result.THEME_DIRECTORY).toBe(DEFAULT_THEME_DIRECTORY);
+        });
+
+        test('expands ~ to actual home directory', () => {
+            const result = getGitConfig(`
+split-diffs.theme-directory=~
+            `);
+            // Should expand to the actual home directory 
+            expect(result.THEME_DIRECTORY).not.toBe('~');
+            expect(result.THEME_DIRECTORY).toBeTruthy();
+        });
+
+        test('expands ~/ to actual home directory with path', () => {
+            const result = getGitConfig(`
+split-diffs.theme-directory=~/my/themes/split-diff
+            `);
+            // Should expand to the actual home directory + path
+            expect(result.THEME_DIRECTORY).not.toContain('~');
+            expect(result.THEME_DIRECTORY).toContain('/my/themes/split-diff');
+        });
+    });
 });

src/getGitConfig.ts

@@ -1,3 +1,4 @@
+import os from 'os';
 import path from 'path';
 import { fileURLToPath } from 'url';
 
@@ -23,6 +24,26 @@ const GIT_CONFIG_LINE_REGEX = new RegExp(
     `${GIT_CONFIG_KEY_PREFIX}\\.([^=]+)=(.*)`
 );
 
+function expandPath(p: string): string {
+    let expanded = p;
+
+    // Expand ~ and ~/ to user home directory
+    if (expanded === '~' || expanded.startsWith('~/')) {
+        expanded = expanded.replace(/^~/, os.homedir());
+    }
+
+    // Expand $VAR and ${VAR} environment variables
+    expanded = expanded.replace(/\$\{([^}]+)\}/g, (_, varName) => {
+        return process.env[varName] || '';
+    });
+    expanded = expanded.replace(/\$([A-Z_][A-Z0-9_]*)/g, (_, varName) => {
+        return process.env[varName] || '';
+    });
+
+    // Return absolute path
+    return path.resolve(expanded);
+}
+
 function extractFromGitConfigString(configString: string) {
     const rawConfig: Record<string, string> = {};
     for (const line of configString.trim().split('\n')) {
@@ -53,8 +74,9 @@ export function getGitConfig(configString: string): GitConfig {
         MIN_LINE_WIDTH: minLineWidth,
         WRAP_LINES: rawConfig['wrap-lines'] !== 'false',
         HIGHLIGHT_LINE_CHANGES: rawConfig['highlight-line-changes'] !== 'false',
-        THEME_DIRECTORY:
-            rawConfig['theme-directory'] ?? DEFAULT_THEME_DIRECTORY,
+        THEME_DIRECTORY: rawConfig['theme-directory'] 
+            ? expandPath(rawConfig['theme-directory'])
+            : DEFAULT_THEME_DIRECTORY,
         THEME_NAME: rawConfig['theme-name'] ?? DEFAULT_THEME_NAME,
         SYNTAX_HIGHLIGHTING_THEME: rawConfig['syntax-highlighting-theme'],
     };