Adds support for custom git installation locations

Also gracefully deals with the times when git isn't in the PATH

src/git/gitLocator.ts

@@ -0,0 +1,74 @@
+import { spawnPromise } from 'spawn-rx';
+import * as path from 'path';
+
+export interface IGit {
+    path: string;
+    version: string;
+}
+
+function parseVersion(raw: string): string {
+    return raw.replace(/^git version /, '');
+}
+
+async function findSpecificGit(path: string): Promise<IGit> {
+    const version = await spawnPromise(path, ['--version']);
+    return {
+        path,
+        version: parseVersion(version.trim())
+    };
+}
+
+async function findGitDarwin(): Promise<IGit> {
+    try {
+        let path = await spawnPromise('which', ['git']);
+        path = path.replace(/^\s+|\s+$/g, '');
+
+        if (path !== '/usr/bin/git') {
+            return findSpecificGit(path);
+        }
+
+        try {
+            await spawnPromise('xcode-select', ['-p']);
+            return findSpecificGit(path);
+        }
+        catch (ex) {
+            if (ex.code === 2) {
+                return Promise.reject('Unable to find git');
+            }
+            return findSpecificGit(path);
+        }
+    }
+    catch (ex) {
+        return Promise.reject('Unable to find git');
+    }
+}
+
+function findSystemGitWin32(basePath: string): Promise<IGit> {
+    if (!basePath) return Promise.reject('Unable to find git');
+    return findSpecificGit(path.join(basePath, 'Git', 'cmd', 'git.exe'));
+}
+
+function findGitWin32(): Promise<IGit> {
+    return findSystemGitWin32(process.env['ProgramW6432'])
+        .then(null, () => findSystemGitWin32(process.env['ProgramFiles(x86)']))
+        .then(null, () => findSystemGitWin32(process.env['ProgramFiles']))
+        .then(null, () => findSpecificGit('git'));
+}
+
+export async function findGitPath(path?: string): Promise<IGit> {
+    try {
+        return await findSpecificGit(path || 'git');
+    }
+    catch (ex) {
+        try {
+            switch (process.platform) {
+                case 'darwin': return await findGitDarwin();
+                case 'win32': return await findGitWin32();
+                default: return Promise.reject('Unable to find git');
+            }
+        }
+        catch (ex) {
+            return Promise.reject('Unable to find git');
+        }
+    }
+}