From 15e2076e871b88be9b6fff02d1acb605ad9fb365 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Tue, 23 Sep 2014 22:10:32 -0700
Subject: [PATCH] Allow "cycles" through dev-deps

Development dependencies can never be the root of a cycle because nothing
depends on a development dependency, so there's no need to track the start of a
cycle at the edge going out to a development dependency.

If a cycle is later detected, it will still be reported.
---
 src/cargo/core/resolver.rs  | 20 +++++++++++++-------
 tests/test_cargo_compile.rs |  4 ++--
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/src/cargo/core/resolver.rs b/src/cargo/core/resolver.rs
index d33bfe618..d2af447b6 100644
--- a/src/cargo/core/resolver.rs
+++ b/src/cargo/core/resolver.rs
@@ -315,12 +315,6 @@ fn resolve_deps<'a, R: Registry>(parent: &Summary,
                                  method: ResolveMethod,
                                  ctx: &mut Context<'a, R>)
                                  -> CargoResult<()> {
-    // Dependency graphs are required to be a DAG
-    if !ctx.visited.insert(parent.get_package_id().clone()) {
-        return Err(human(format!("Cyclic package dependency: package `{}` \
-                                  depends on itself", parent.get_package_id())))
-    }
-
     let dev_deps = match method {
         ResolveEverything => true,
         ResolveRequired(dev_deps, _, _) => dev_deps,
@@ -402,13 +396,25 @@ fn resolve_deps<'a, R: Registry>(parent: &Summary,
             ctx.seen.insert((name, source_id), version.clone());
             ctx.resolve.graph.add(summary.get_package_id().clone(), []);
         }
+
+        // Dependency graphs are required to be a DAG. Non-transitive
+        // dependencies (dev-deps), however, can never introduce a cycle, so we
+        // skip them.
+        if dep.is_transitive() &&
+           !ctx.visited.insert(summary.get_package_id().clone()) {
+            return Err(human(format!("Cyclic package dependency: package `{}` \
+                                      depends on itself",
+                                     summary.get_package_id())))
+        }
         try!(resolve_deps(summary,
                           ResolveRequired(false, dep.get_features(),
                                           dep.uses_default_features()),
                           ctx));
+        if dep.is_transitive() {
+            ctx.visited.remove(summary.get_package_id());
+        }
     }
 
-    ctx.visited.remove(parent.get_package_id());
     Ok(())
 }
 
diff --git a/tests/test_cargo_compile.rs b/tests/test_cargo_compile.rs
index 7a9ed2a03..764e7524c 100644
--- a/tests/test_cargo_compile.rs
+++ b/tests/test_cargo_compile.rs
@@ -1082,8 +1082,8 @@ test!(self_dependency {
         "#)
         .file("src/test.rs", "fn main() {}");
     assert_that(p.cargo_process("build"),
-                execs().with_status(101).with_stderr("\
-Cyclic package dependency: package `test v0.0.0 ([..])` depends on itself
+                execs().with_status(0).with_stdout("\
+[..] test v0.0.0 ([..])
 "));
 })
 
-- 
2.30.2