Respect .gitignore during cargo new

When running `cargo new`, we check to see if you are inside a git
repository. If you are, we do not initialize a new git repo for
your project unless you specifically asked for it using --vcs.
(See #1210 for more background).

This commit changes that behavior to *also* create a new repo if
the project would be an ignored path in the parent repository.
This way, if your home directory is a git repository, as long as
you have ignored the directory you are creating a new project in,
we will instantiate a git repository without you having to
specifically request it.

src/cargo/ops/cargo_new.rs

@@ -409,8 +409,19 @@ pub fn init(opts: &NewOptions, config: &Config) -> CargoResult<()> {
     Ok(())
 }
 
+// Check if we are in an existing repo. We define that to be true if either:
+//
+// 1. We are in a git repo and the path to the new project is not an ignored
+//    path in that repo.
+// 2. We are in an HG repo.
 pub fn existing_vcs_repo(path: &Path, cwd: &Path) -> bool {
-    GitRepo::discover(path, cwd).is_ok() || HgRepo::discover(path, cwd).is_ok()
+    fn in_git_repo(path: &Path, cwd: &Path) -> bool {
+        if let Ok(repo) = GitRepo::discover(path, cwd) {
+            repo.is_path_ignored(path).map(|ignored| !ignored).unwrap_or(true)
+        } else { false }
+    }
+
+    in_git_repo(path, cwd) || HgRepo::discover(path, cwd).is_ok()
 }
 
 fn mk(config: &Config, opts: &MkOptions) -> CargoResult<()> {

tests/testsuite/fix.rs

@@ -826,7 +826,7 @@ fn does_not_warn_about_clean_working_directory() {
 fn does_not_warn_about_dirty_ignored_files() {
     let p = project()
         .file("src/lib.rs", "pub fn foo() {}")
-        .file(".gitignore", "foo\n")
+        .file(".gitignore", "bar\n")
         .build();
 
     let repo = git2::Repository::init(&p.root()).unwrap();
@@ -836,7 +836,7 @@ fn does_not_warn_about_dirty_ignored_files() {
     drop(cfg);
     git::add(&repo);
     git::commit(&repo);
-    File::create(p.root().join("foo")).unwrap();
+    File::create(p.root().join("bar")).unwrap();
 
     assert_that(
         p.cargo("fix"),

tests/testsuite/new.rs

@@ -495,6 +495,36 @@ fn subpackage_no_git() {
     );
 }
 
+#[test]
+fn subpackage_git_with_gitignore() {
+    assert_that(
+        cargo_process("new").arg("foo").env("USER", "foo"),
+        execs().with_status(0),
+    );
+
+    let gitignore = paths::root().join("foo").join(".gitignore");
+    fs::write(gitignore, b"components").unwrap();
+
+    let subpackage = paths::root().join("foo").join("components");
+    fs::create_dir(&subpackage).unwrap();
+    assert_that(
+        cargo_process("new")
+            .arg("foo/components/subcomponent")
+            .env("USER", "foo"),
+        execs().with_status(0),
+    );
+
+    assert_that(
+        &paths::root().join("foo").join("components").join("subcomponent").join(".git"),
+        existing_dir(),
+    );
+    assert_that(
+        &paths::root().join("foo").join("components").join("subcomponent").join(".gitignore"),
+        existing_file(),
+    );
+
+}
+
 #[test]
 fn subpackage_git_with_vcs_arg() {
     assert_that(