Add patch for dev-lang/rust that fixes git problem in cargo

This change adds a patch for a fix in cargo that causes the branches in
a git repository for a cargo managed project to potentially be messed up
during a rebase --exec cycle when a git fetch is invoked as part of the
command being executed.
This problem is tracked upstream as issue #7072 [1].

[1] rust-lang/cargo#7072

patches/dev-lang/rust/cargo_-_clean-environment-when-git-fetch-with-cli-is-used.patch

@@ -0,0 +1,92 @@
+From 00fd31dd9bc757d8b8a3c35466daec09aa965d83 Mon Sep 17 00:00:00 2001
+From: Eric Huss <eric@huss.org>
+Date: Sat, 29 Jun 2019 13:32:21 -0700
+Subject: [PATCH] Clean environment when git-fetch-with-cli is used.
+
+---
+ src/cargo/sources/git/utils.rs | 11 ++++++++
+ tests/testsuite/git.rs         | 49 ++++++++++++++++++++++++++++++++++
+ 2 files changed, 60 insertions(+)
+
+diff --git a/src/tools/cargo/src/cargo/sources/git/utils.rs b/src/tools/cargo/src/cargo/sources/git/utils.rs
+index a71e49..5ad3ed 100644
+--- a/src/tools/cargo/src/cargo/sources/git/utils.rs
++++ b/src/tools/cargo/src/cargo/sources/git/utils.rs
+@@ -770,6 +770,17 @@ fn fetch_with_cli(
+         .arg("--update-head-ok") // see discussion in #2078
+         .arg(url.to_string())
+         .arg(refspec)
++        // If cargo is run by git (for example, the `exec` command in `git
++        // rebase`), the GIT_DIR is set by git and will point to the wrong
++        // location (this takes precedence over the cwd). Make sure this is
++        // unset so git will look at cwd for the repo.
++        .env_remove("GIT_DIR")
++        // The reset of these may not be necessary, but I'm including them
++        // just to be extra paranoid and avoid any issues.
++        .env_remove("GIT_WORK_TREE")
++        .env_remove("GIT_INDEX_FILE")
++        .env_remove("GIT_OBJECT_DIRECTORY")
++        .env_remove("GIT_ALTERNATE_OBJECT_DIRECTORIES")
+         .cwd(repo.path());
+     config
+         .shell()
+diff --git a/src/tools/cargo/tests/testsuite/git.rs b/src/tools/cargo/tests/testsuite/git.rs
+index 8cdd3f..9762ea 100644
+--- a/src/tools/cargo/tests/testsuite/git.rs
++++ b/src/tools/cargo/tests/testsuite/git.rs
+@@ -2694,3 +2694,52 @@ fn git_with_cli_force() {
+     p.cargo("build").run();
+     p.rename_run("foo", "foo2").with_stdout("two").run();
+ }
++
++#[cargo_test]
++fn git_fetch_cli_env_clean() {
++    if disable_git_cli() {
++        return;
++    }
++    // This tests that git-fetch-with-cli works when GIT_DIR environment
++    // variable is set (for whatever reason).
++    let git_dep = git::new("dep1", |project| {
++        project
++            .file("Cargo.toml", &basic_manifest("dep1", "0.5.0"))
++            .file("src/lib.rs", "")
++    })
++    .unwrap();
++
++    let git_proj = git::new("foo", |project| {
++        project
++            .file(
++                "Cargo.toml",
++                &format!(
++                    r#"
++                    [package]
++                    name = "foo"
++                    version = "0.1.0"
++                    [dependencies]
++                    dep1 = {{ git = '{}' }}
++                    "#,
++                    git_dep.url()
++                ),
++            )
++            .file("src/lib.rs", "pub extern crate dep1;")
++            .file(
++                ".cargo/config",
++                "
++                [net]
++                git-fetch-with-cli = true
++                ",
++            )
++    })
++    .unwrap();
++
++    // The directory set here isn't too important. Pointing to our own git
++    // directory causes git to be confused and fail. Can also point to an
++    // empty directory, or a nonexistent one.
++    git_proj
++        .cargo("fetch")
++        .env("GIT_DIR", git_proj.root().join(".git"))
++        .run();
++}
+-- 
+2.21.0
+