Add support for loading custom themes

Author: banga

README.md

@@ -171,6 +171,17 @@ git config split-diffs.theme-name monochrome-light
 
 ![Screenshot of Monochrome Light theme](screenshots/monochrome-light.png?raw=true)
 
+## Custom Themes
+
+Default themes are loaded from the `git-split-diffs` bundle. To load a custom theme, set `theme-directory` in git config and create a `{theme-name}.json` file in that directory with the theme's definition. You can use one of the existing themes in [themes/](https://github.com/banga/git-split-diffs/tree/main/themes) as a starting point.
+
+```
+git config split-diffs.theme-directory </path/to/theme>
+git config split-diffs.theme-name <name>
+```
+
+This will use `/path/to/theme/name.json` as the theme.
+
 ## Performance
 
 Tested by measuring the time it took to pipe the output `git log -p` to `/dev/null` via `git-split-diffs` with the default theme:
@@ -191,6 +202,10 @@ See [#narrow-terminals](#narrow-terminals)
 
 Text coloring is implemented using Chalk which supports [various levels of color](https://github.com/chalk/chalk#supportscolor). If Chalk is producing fewer colors than your terminal supports, try overriding Chalk's detection using a variation of the `--color` flag, e.g. `--color=16m` for true color. See Chalk's documentation or [this useful gist on terminal support](https://gist.github.com/XVilka/8346728) if issues persist.
 
+### Want to remove background colors from a theme?
+
+See [#custom-themes](#custom-themes) for instructions on customizing themes. Removing `backgroundColor` should usually work.
+
 ## Acknowledgements
 
 -   [diff-so-fancy](https://github.com/so-fancy/diff-so-fancy) for showing what's possible

src/getConfig.ts

@@ -8,16 +8,14 @@ export type Config = Theme & {
     HIGHLIGHT_LINE_CHANGES: boolean;
 };
 
-export const DEFAULT_THEME_NAME = 'dark';
-
 export const CONFIG_DEFAULTS: Omit<Config, keyof Theme> = {
     MIN_LINE_WIDTH: 80,
     WRAP_LINES: true,
     HIGHLIGHT_LINE_CHANGES: true,
 };
 
 export function getConfig(gitConfig: GitConfig): Config {
-    const theme = loadTheme(gitConfig.THEME_NAME ?? DEFAULT_THEME_NAME);
+    const theme = loadTheme(gitConfig.THEME_DIRECTORY, gitConfig.THEME_NAME);
 
     return {
         ...CONFIG_DEFAULTS,

src/getGitConfig.test.ts

@@ -1,6 +1,7 @@
-import { DEFAULT_THEME_NAME } from './getConfig';
 import {
     DEFAULT_MIN_LINE_WIDTH,
+    DEFAULT_THEME_DIRECTORY,
+    DEFAULT_THEME_NAME,
     GitConfig,
     getGitConfig,
 } from './getGitConfig';
@@ -10,6 +11,7 @@ const DEFAULT_CONFIG: GitConfig = {
     HIGHLIGHT_LINE_CHANGES: true,
     MIN_LINE_WIDTH: DEFAULT_MIN_LINE_WIDTH,
     THEME_NAME: DEFAULT_THEME_NAME,
+    THEME_DIRECTORY: DEFAULT_THEME_DIRECTORY,
 };
 
 describe('getGitConfig', () => {
@@ -24,13 +26,15 @@ split-diffs.wrap-lines=false
 split-diffs.highlight-line-changes=false
 split-diffs.min-line-width=40
 split-diffs.theme-name=arctic
+split-diffs.theme-directory=/tmp
 split-diffs.syntax-highlighting-theme=dark-plus
             `)
         ).toEqual({
             WRAP_LINES: false,
             HIGHLIGHT_LINE_CHANGES: false,
             MIN_LINE_WIDTH: 40,
             THEME_NAME: 'arctic',
+            THEME_DIRECTORY: '/tmp',
             SYNTAX_HIGHLIGHTING_THEME: 'dark-plus',
         });
     });

src/getGitConfig.ts

@@ -1,12 +1,21 @@
+import path from 'path';
+import { fileURLToPath } from 'url';
+
 export type GitConfig = {
     MIN_LINE_WIDTH: number;
     WRAP_LINES: boolean;
     HIGHLIGHT_LINE_CHANGES: boolean;
+    THEME_DIRECTORY: string;
     THEME_NAME: string;
     SYNTAX_HIGHLIGHTING_THEME?: string;
 };
 
 export const DEFAULT_MIN_LINE_WIDTH = 80;
+export const DEFAULT_THEME_DIRECTORY = path.resolve(
+    path.dirname(fileURLToPath(import.meta.url)),
+    '..',
+    'themes'
+);
 export const DEFAULT_THEME_NAME = 'dark';
 
 const GIT_CONFIG_KEY_PREFIX = 'split-diffs';
@@ -44,6 +53,8 @@ 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_NAME: rawConfig['theme-name'] ?? DEFAULT_THEME_NAME,
         SYNTAX_HIGHLIGHTING_THEME: rawConfig['syntax-highlighting-theme'],
     };

src/previewTheme.ts

@@ -6,15 +6,20 @@ import { Config } from './getConfig';
 import { getContextForConfig } from './context';
 import { loadTheme } from './themes';
 import { transformContentsStreaming } from './transformContentsStreaming';
+import { DEFAULT_THEME_DIRECTORY } from './getGitConfig';
 
 const CONFIG = {
     MIN_LINE_WIDTH: 40,
     WRAP_LINES: true,
     HIGHLIGHT_LINE_CHANGES: true,
 };
 
-async function previewTheme(themeName: string, content: string) {
-    const theme = loadTheme(themeName);
+async function previewTheme(
+    themeDirectory: string,
+    themeName: string,
+    content: string
+) {
+    const theme = loadTheme(themeDirectory, themeName);
 
     const { rows, columns } = terminalSize();
     const config: Config = {
@@ -41,19 +46,22 @@ async function previewTheme(themeName: string, content: string) {
 }
 
 function main() {
-    if (process.argv.length !== 4) {
-        console.error(`Usage: ${process.argv[1]} <sha> <theme name>`);
+    if (process.argv.length < 4) {
+        console.error(
+            `Usage: ${process.argv[1]} <sha> <theme name> [theme directory]`
+        );
         process.exit(1);
     }
 
-    const [, , sha, themeName] = process.argv;
+    const [, , sha, themeName, themeDirectory = DEFAULT_THEME_DIRECTORY] =
+        process.argv;
 
     const content = execSync(`git show ${sha}`).toString();
 
     // Clear screen
     process.stdout.write('\x1bc');
 
-    previewTheme(themeName, content);
+    previewTheme(themeDirectory, themeName, content);
 }
 
 main();

src/themes.ts

@@ -1,14 +1,8 @@
 import * as assert from 'assert';
 import * as path from 'path';
 import * as fs from 'fs';
-import { fileURLToPath } from 'url';
 import * as shiki from 'shiki';
 
-const THEMES_DIR = path.resolve(
-    path.dirname(fileURLToPath(import.meta.url)),
-    '..',
-    'themes'
-);
 /**
  * Colors are always specified as hex strings
  */
@@ -165,14 +159,17 @@ export function parseColorDefinition(definition: ColorDefinition): ThemeColor {
     };
 }
 
-function loadThemeDefinition(themeName: string): ThemeDefinition {
+function loadThemeDefinition(
+    themesDir: string,
+    themeName: string
+): ThemeDefinition {
     return JSON.parse(
-        fs.readFileSync(path.join(THEMES_DIR, `${themeName}.json`)).toString()
+        fs.readFileSync(path.join(themesDir, `${themeName}.json`)).toString()
     ) as ThemeDefinition;
 }
 
-export function loadTheme(themeName: string): Theme {
-    const themeDefinition = loadThemeDefinition(themeName);
+export function loadTheme(themesDir: string, themeName: string): Theme {
+    const themeDefinition = loadThemeDefinition(themesDir, themeName);
 
     const theme: Partial<Theme> = {
         SYNTAX_HIGHLIGHTING_THEME: themeDefinition.SYNTAX_HIGHLIGHTING_THEME,