From c0cc8ffe24ff795b9d0d5ca9da57485049fd3c97 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Mon, 23 Jan 2017 09:25:14 -0800
Subject: [PATCH] Handle `rev` being a `tag`

Previously if a rev was specified as a tag then we'd trip an assertion because
resetting to that tag would reset to the tag that the commit pointed to, which
would then cause the head id of the repo to be different than what we thought it
was.

Instead, we handle the case where a `rev` specification is a tag explicitly by
using the tag's target id as the revision that we're going to check out, not the
id of the tag itself.

Closes #3580
---
 src/cargo/sources/git/utils.rs |  5 +++-
 tests/git.rs                   | 45 ++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/src/cargo/sources/git/utils.rs b/src/cargo/sources/git/utils.rs
index 3b3b005f3..03fe6a5e2 100644
--- a/src/cargo/sources/git/utils.rs
+++ b/src/cargo/sources/git/utils.rs
@@ -217,7 +217,10 @@ impl GitDatabase {
             }
             GitReference::Rev(ref s) => {
                 let obj = self.repo.revparse_single(s)?;
-                obj.id()
+                match obj.as_tag() {
+                    Some(tag) => tag.target_id(),
+                    None => obj.id(),
+                }
             }
         };
         Ok(GitRevision(id))
diff --git a/tests/git.rs b/tests/git.rs
index f56c67fea..e1aff7240 100644
--- a/tests/git.rs
+++ b/tests/git.rs
@@ -1826,3 +1826,48 @@ fn add_a_git_dep() {
 
     assert_that(p.cargo("build"), execs().with_status(0));
 }
+
+#[test]
+fn two_at_rev_instead_of_tag() {
+    let git = git::new("git", |p| {
+        p.file("Cargo.toml", r#"
+            [project]
+            name = "git1"
+            version = "0.5.0"
+            authors = []
+        "#)
+        .file("src/lib.rs", "")
+        .file("a/Cargo.toml", r#"
+            [project]
+            name = "git2"
+            version = "0.5.0"
+            authors = []
+        "#)
+        .file("a/src/lib.rs", "")
+    }).unwrap();
+
+    // Make a tag corresponding to the current HEAD
+    let repo = git2::Repository::open(&git.root()).unwrap();
+    let head = repo.head().unwrap().target().unwrap();
+    repo.tag("v0.1.0",
+             &repo.find_object(head, None).unwrap(),
+             &repo.signature().unwrap(),
+             "make a new tag",
+             false).unwrap();
+
+    let p = project("foo")
+        .file("Cargo.toml", &format!(r#"
+            [package]
+            name = "foo"
+            version = "0.0.1"
+            authors = []
+
+            [dependencies]
+            git1 = {{ git = '{0}', rev = 'v0.1.0' }}
+            git2 = {{ git = '{0}', rev = 'v0.1.0' }}
+        "#, git.url()))
+        .file("src/lib.rs", "");
+
+    assert_that(p.cargo_process("generate-lockfile"), execs().with_status(0));
+    assert_that(p.cargo("build").arg("-v"), execs().with_status(0));
+}