From dcb3799eaa8038c33c5d31df76e1c1700079b06d Mon Sep 17 00:00:00 2001
From: Marcel Hlopko <hlopko@google.com>
Date: Mon, 21 Jun 2021 22:20:59 +0200
Subject: [PATCH 1/8] Add a test

---
 .../{ => aspect_traversal_test}/BUILD.bazel   |  0
 .../extra_proc_macro_dep.rs                   |  0
 .../extra_test_dep.rs                         |  0
 .../{ => aspect_traversal_test}/lib_dep.rs    |  0
 .../{ => aspect_traversal_test}/mylib.rs      |  0
 .../proc_macro_dep.rs                         |  0
 .../rust_project_json_test.rs                 |  2 +-
 .../merging_crates_test/BUILD.bazel           | 37 +++++++++++++++++++
 .../merging_crates_test/extra_test_dep.rs     |  1 +
 .../merging_crates_test/lib_dep.rs            |  1 +
 .../merging_crates_test/mylib.rs              |  1 +
 .../rust_project_json_test.rs                 | 21 +++++++++++
 12 files changed, 62 insertions(+), 1 deletion(-)
 rename test/rust_analyzer/{ => aspect_traversal_test}/BUILD.bazel (100%)
 rename test/rust_analyzer/{ => aspect_traversal_test}/extra_proc_macro_dep.rs (100%)
 rename test/rust_analyzer/{ => aspect_traversal_test}/extra_test_dep.rs (100%)
 rename test/rust_analyzer/{ => aspect_traversal_test}/lib_dep.rs (100%)
 rename test/rust_analyzer/{ => aspect_traversal_test}/mylib.rs (100%)
 rename test/rust_analyzer/{ => aspect_traversal_test}/proc_macro_dep.rs (100%)
 rename test/rust_analyzer/{ => aspect_traversal_test}/rust_project_json_test.rs (91%)
 create mode 100644 test/rust_analyzer/merging_crates_test/BUILD.bazel
 create mode 100644 test/rust_analyzer/merging_crates_test/extra_test_dep.rs
 create mode 100644 test/rust_analyzer/merging_crates_test/lib_dep.rs
 create mode 100644 test/rust_analyzer/merging_crates_test/mylib.rs
 create mode 100644 test/rust_analyzer/merging_crates_test/rust_project_json_test.rs

diff --git a/test/rust_analyzer/BUILD.bazel b/test/rust_analyzer/aspect_traversal_test/BUILD.bazel
similarity index 100%
rename from test/rust_analyzer/BUILD.bazel
rename to test/rust_analyzer/aspect_traversal_test/BUILD.bazel
diff --git a/test/rust_analyzer/extra_proc_macro_dep.rs b/test/rust_analyzer/aspect_traversal_test/extra_proc_macro_dep.rs
similarity index 100%
rename from test/rust_analyzer/extra_proc_macro_dep.rs
rename to test/rust_analyzer/aspect_traversal_test/extra_proc_macro_dep.rs
diff --git a/test/rust_analyzer/extra_test_dep.rs b/test/rust_analyzer/aspect_traversal_test/extra_test_dep.rs
similarity index 100%
rename from test/rust_analyzer/extra_test_dep.rs
rename to test/rust_analyzer/aspect_traversal_test/extra_test_dep.rs
diff --git a/test/rust_analyzer/lib_dep.rs b/test/rust_analyzer/aspect_traversal_test/lib_dep.rs
similarity index 100%
rename from test/rust_analyzer/lib_dep.rs
rename to test/rust_analyzer/aspect_traversal_test/lib_dep.rs
diff --git a/test/rust_analyzer/mylib.rs b/test/rust_analyzer/aspect_traversal_test/mylib.rs
similarity index 100%
rename from test/rust_analyzer/mylib.rs
rename to test/rust_analyzer/aspect_traversal_test/mylib.rs
diff --git a/test/rust_analyzer/proc_macro_dep.rs b/test/rust_analyzer/aspect_traversal_test/proc_macro_dep.rs
similarity index 100%
rename from test/rust_analyzer/proc_macro_dep.rs
rename to test/rust_analyzer/aspect_traversal_test/proc_macro_dep.rs
diff --git a/test/rust_analyzer/rust_project_json_test.rs b/test/rust_analyzer/aspect_traversal_test/rust_project_json_test.rs
similarity index 91%
rename from test/rust_analyzer/rust_project_json_test.rs
rename to test/rust_analyzer/aspect_traversal_test/rust_project_json_test.rs
index 758adee4b1..2dbe59a2d4 100644
--- a/test/rust_analyzer/rust_project_json_test.rs
+++ b/test/rust_analyzer/aspect_traversal_test/rust_project_json_test.rs
@@ -2,7 +2,7 @@ use runfiles::Runfiles;
 
 fn main() {
     let r = Runfiles::create().unwrap();
-    let rust_project_path = r.rlocation("rules_rust/test/rust_analyzer/rust-project.json");
+    let rust_project_path = r.rlocation("rules_rust/test/rust_analyzer/aspect_traversal_test/rust-project.json");
 
     let content = std::fs::read_to_string(&rust_project_path)
         .expect(&format!("couldn't open {:?}", &rust_project_path));
diff --git a/test/rust_analyzer/merging_crates_test/BUILD.bazel b/test/rust_analyzer/merging_crates_test/BUILD.bazel
new file mode 100644
index 0000000000..2f93da81ec
--- /dev/null
+++ b/test/rust_analyzer/merging_crates_test/BUILD.bazel
@@ -0,0 +1,37 @@
+load("//rust:defs.bzl", "rust_analyzer", "rust_library", "rust_proc_macro", "rust_test")
+
+rust_library(
+    name = "mylib",
+    srcs = ["mylib.rs"],
+    deps = [":lib_dep"],
+)
+
+rust_library(
+    name = "lib_dep",
+    srcs = ["lib_dep.rs"],
+)
+
+rust_test(
+    name = "mylib_test",
+    crate = ":mylib",
+    deps = [":extra_test_dep"],
+)
+
+rust_library(
+    name = "extra_test_dep",
+    srcs = ["extra_test_dep.rs"],
+)
+
+rust_analyzer(
+    name = "rust_analyzer",
+    testonly = True,
+    targets = [":mylib_test", ":mylib", ],
+)
+
+rust_test(
+    name = "rust_project_json_test",
+    srcs = ["rust_project_json_test.rs"],
+    data = [":rust-project.json"],
+    edition = "2018",
+    deps = ["//tools/runfiles"],
+)
diff --git a/test/rust_analyzer/merging_crates_test/extra_test_dep.rs b/test/rust_analyzer/merging_crates_test/extra_test_dep.rs
new file mode 100644
index 0000000000..8b13789179
--- /dev/null
+++ b/test/rust_analyzer/merging_crates_test/extra_test_dep.rs
@@ -0,0 +1 @@
+
diff --git a/test/rust_analyzer/merging_crates_test/lib_dep.rs b/test/rust_analyzer/merging_crates_test/lib_dep.rs
new file mode 100644
index 0000000000..8b13789179
--- /dev/null
+++ b/test/rust_analyzer/merging_crates_test/lib_dep.rs
@@ -0,0 +1 @@
+
diff --git a/test/rust_analyzer/merging_crates_test/mylib.rs b/test/rust_analyzer/merging_crates_test/mylib.rs
new file mode 100644
index 0000000000..8b13789179
--- /dev/null
+++ b/test/rust_analyzer/merging_crates_test/mylib.rs
@@ -0,0 +1 @@
+
diff --git a/test/rust_analyzer/merging_crates_test/rust_project_json_test.rs b/test/rust_analyzer/merging_crates_test/rust_project_json_test.rs
new file mode 100644
index 0000000000..c57e01c7ab
--- /dev/null
+++ b/test/rust_analyzer/merging_crates_test/rust_project_json_test.rs
@@ -0,0 +1,21 @@
+use runfiles::Runfiles;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_deps_of_crate_and_its_test_are_merged() {
+        let r = Runfiles::create().unwrap();
+        let rust_project_path = r.rlocation("rules_rust/test/rust_analyzer/merging_crates_test/rust-project.json");
+
+        let content = std::fs::read_to_string(&rust_project_path)
+            .expect(&format!("couldn't open {:?}", &rust_project_path));
+
+        for dep in &["lib_dep","", "extra_test_dep"] {
+            if !content.contains(dep) {
+                panic!("expected rust-project.json to contain {}.", dep);
+            }
+        }
+    }
+}

From 538219f84172e6c1043220bdbc61e181e6506261 Mon Sep 17 00:00:00 2001
From: Marcel Hlopko <hlopko@google.com>
Date: Tue, 22 Jun 2021 09:22:57 +0200
Subject: [PATCH 2/8] Fix rust analyzer

---
 rust/private/rust_analyzer.bzl                | 106 ++++++++++++------
 .../merging_crates_test/BUILD.bazel           |   8 +-
 .../rust_project_json_test.rs                 |   8 +-
 .../merging_crates_test_reversed/BUILD.bazel  |  41 +++++++
 .../extra_test_dep.rs                         |   1 +
 .../merging_crates_test_reversed/lib_dep.rs   |   1 +
 .../merging_crates_test_reversed/mylib.rs     |   1 +
 .../rust_project_json_test.rs                 |  19 ++++
 8 files changed, 142 insertions(+), 43 deletions(-)
 create mode 100644 test/rust_analyzer/merging_crates_test_reversed/BUILD.bazel
 create mode 100644 test/rust_analyzer/merging_crates_test_reversed/extra_test_dep.rs
 create mode 100644 test/rust_analyzer/merging_crates_test_reversed/lib_dep.rs
 create mode 100644 test/rust_analyzer/merging_crates_test_reversed/mylib.rs
 create mode 100644 test/rust_analyzer/merging_crates_test_reversed/rust_project_json_test.rs

diff --git a/rust/private/rust_analyzer.bzl b/rust/private/rust_analyzer.bzl
index ea9c6b29d8..943557161a 100644
--- a/rust/private/rust_analyzer.bzl
+++ b/rust/private/rust_analyzer.bzl
@@ -20,6 +20,7 @@ given targets. This file can be consumed by rust-analyzer as an alternative
 to Cargo.toml files.
 """
 
+load("@bazel_skylib//lib:collections.bzl", "collections")
 load("//rust/platform:triple_mappings.bzl", "system_to_dylib_ext", "triple_to_system")
 load("//rust/private:common.bzl", "rust_common")
 load("//rust/private:rustc.bzl", "BuildInfo")
@@ -44,7 +45,8 @@ def _rust_analyzer_aspect_impl(target, ctx):
 
     toolchain = find_toolchain(ctx)
 
-    # Always add test & debug_assertions (like here: https://github.com/rust-analyzer/rust-analyzer/blob/505ff4070a3de962dbde66f08b6550cda2eb4eab/crates/project_model/src/lib.rs#L379-L381)
+    # Always add test & debug_assertions (like here:
+    # https://github.com/rust-analyzer/rust-analyzer/blob/505ff4070a3de962dbde66f08b6550cda2eb4eab/crates/project_model/src/lib.rs#L379-L381)
     cfgs = ["test", "debug_assertions"]
     if hasattr(ctx.rule.attr, "crate_features"):
         cfgs += ['feature="{}"'.format(f) for f in ctx.rule.attr.crate_features]
@@ -116,51 +118,79 @@ def _crate_id(crate_info):
     """
     return "ID-" + crate_info.root.path
 
-def create_crate(ctx, info, crate_mapping):
-    """Creates a crate in the rust-project.json format
+_DepRefInfo = provider(
+    doc = "RustAnalyzerInfo holds rust crate metadata for targets",
+    fields = {
+        "crate": "BuildInfo: build info for this crate if present",
+        "name": "List[String]: features or other compilation --cfg settings",
+    },
+)
+
+def _create_crate(ctx, infos, crate_mapping):
+    """Creates a crate in the rust-project.json format.
+
+    It can happen a single source file is present in multiple crates - there can
+    be a `rust_library` with a `lib.rs` file, and a `rust_test` for the `test`
+    module in that file. Tests can declare more dependencies than what library
+    had. Therefore we had to collect all RustAnalyzerInfos for a given crate
+    and take deps from all of them.
+
+    There's one exception - if the dependency is the same crate name as the
+    the crate being processed, we don't add it as a dependency to itself. This is
+    common and expected - `rust_test.crate` pointing to the `rust_library`.
 
     Args:
         ctx (ctx): The rule context
-        info (RustAnalyzerInfo): The crate RustAnalyzerInfo for the current crate
+        infos (list of RustAnalyzerInfos): RustAnalyzerInfos for the current crate
         crate_mapping (dict): A dict of {String:Int} that memoizes crates for deps.
 
     Returns:
         (dict) The crate rust-project.json representation
     """
+    canonical_info = infos[0]
+    crate_name = canonical_info.crate.name
     crate = dict()
-    crate["display_name"] = info.crate.name
-    crate["edition"] = info.crate.edition
+    crate["display_name"] = crate_name
+    crate["edition"] = canonical_info.crate.edition
     crate["env"] = {}
 
     # Switch on external/ to determine if crates are in the workspace or remote.
     # TODO: Some folks may want to override this for vendored dependencies.
-    if info.crate.root.path.startswith("external/"):
+    root_path = canonical_info.crate.root.path
+    root_dirname = canonical_info.crate.root.dirname
+    if root_path.startswith("external/"):
         crate["is_workspace_member"] = False
-        crate["root_module"] = _exec_root_tmpl + info.crate.root.path
-        crate_root = _exec_root_tmpl + info.crate.root.dirname
+        crate["root_module"] = _exec_root_tmpl + root_path
+        crate_root = _exec_root_tmpl + root_dirname
     else:
         crate["is_workspace_member"] = True
-        crate["root_module"] = info.crate.root.path
-        crate_root = info.crate.root.dirname
+        crate["root_module"] = root_path
+        crate_root = root_dirname
 
-    if info.build_info != None:
-        crate["env"].update({"OUT_DIR": _exec_root_tmpl + info.build_info.out_dir.path})
+    if canonical_info.build_info != None:
+        out_dir_path = canonical_info.build_info.out_dir.path
+        crate["env"].update({"OUT_DIR": _exec_root_tmpl + out_dir_path})
         crate["source"] = {
             # We have to tell rust-analyzer about our out_dir since it's not under the crate root.
             "exclude_dirs": [],
-            "include_dirs": [crate_root, _exec_root_tmpl + info.build_info.out_dir.path],
+            "include_dirs": [crate_root, _exec_root_tmpl + out_dir_path],
         }
-    crate["env"].update(info.env)
+    crate["env"].update(canonical_info.env)
+
+    duplicated_deps = []
+    for info in infos:
+        for dep in info.deps:
+            if dep.crate.name == crate_name:
+                continue
+            duplicated_deps.append(_DepRefInfo(crate = crate_mapping[_crate_id(dep.crate)], name = dep.crate.name))
+
+    deps = [{"crate": d.crate, "name": d.name} for d in collections.uniq(duplicated_deps)]
 
-    deps = [
-        {"crate": crate_mapping[_crate_id(d.crate)], "name": d.crate.name}
-        for d in info.deps
-    ]
     crate["deps"] = deps
-    crate["cfg"] = info.cfgs
+    crate["cfg"] = canonical_info.cfgs
     crate["target"] = find_toolchain(ctx).target_triple
-    if info.proc_macro_dylib_path != None:
-        crate["proc_macro_dylib_path"] = _exec_root_tmpl + info.proc_macro_dylib_path
+    if canonical_info.proc_macro_dylib_path != None:
+        crate["proc_macro_dylib_path"] = _exec_root_tmpl + canonical_info.proc_macro_dylib_path
     return crate
 
 # This implementation is incomplete because in order to get rustc env vars we
@@ -181,29 +211,33 @@ def _rust_analyzer_impl(ctx):
     if rust_toolchain.rustc_srcs.label.workspace_root:
         sysroot_src = _exec_root_tmpl + rust_toolchain.rustc_srcs.label.workspace_root + "/" + sysroot_src
 
-    # Gather all crates and their dependencies into an array.
-    # Dependencies are referenced by index, so leaves should come first.
-    crates = []
+    # Groups of RustAnalyzerInfos with the same _crate_id().
+    rust_analyzer_info_groups = []
+
+    # Dict from _crate_id() to the index of a RustAnalyzerInfo group in `rust_analyzer_info_groups`.
     crate_mapping = dict()
+
+    # Dependencies are referenced by index, so leaves should come first.
     idx = 0
     for target in ctx.attr.targets:
         if RustAnalyzerInfo not in target:
             continue
 
-        # Add this crate's transitive deps to the crate mapping and output.
-        for dep_info in target[RustAnalyzerInfo].transitive_deps.to_list():
-            crate_id = _crate_id(dep_info.crate)
+        for info in depset(
+            direct = [target[RustAnalyzerInfo]],
+            transitive = [target[RustAnalyzerInfo].transitive_deps],
+            order = "postorder",
+        ).to_list():
+            crate_id = _crate_id(info.crate)
             if crate_id not in crate_mapping:
                 crate_mapping[crate_id] = idx
+                rust_analyzer_info_groups.append([])
                 idx += 1
-                crates.append(create_crate(ctx, dep_info, crate_mapping))
-
-        # Add this crate to the crate mapping and output.
-        crate_id = _crate_id(target[RustAnalyzerInfo].crate)
-        if crate_id not in crate_mapping:
-            crate_mapping[crate_id] = idx
-            idx += 1
-            crates.append(create_crate(ctx, target[RustAnalyzerInfo], crate_mapping))
+            rust_analyzer_info_groups[crate_mapping[crate_id]].append(info)
+
+    crates = []
+    for group in rust_analyzer_info_groups:
+        crates.append(_create_crate(ctx, group, crate_mapping))
 
     # TODO(djmarcin): Use json module once bazel 4.0 is released.
     ctx.actions.write(output = ctx.outputs.filename, content = struct(
diff --git a/test/rust_analyzer/merging_crates_test/BUILD.bazel b/test/rust_analyzer/merging_crates_test/BUILD.bazel
index 2f93da81ec..a54e1932e0 100644
--- a/test/rust_analyzer/merging_crates_test/BUILD.bazel
+++ b/test/rust_analyzer/merging_crates_test/BUILD.bazel
@@ -1,4 +1,4 @@
-load("//rust:defs.bzl", "rust_analyzer", "rust_library", "rust_proc_macro", "rust_test")
+load("//rust:defs.bzl", "rust_analyzer", "rust_library", "rust_test")
 
 rust_library(
     name = "mylib",
@@ -25,7 +25,11 @@ rust_library(
 rust_analyzer(
     name = "rust_analyzer",
     testonly = True,
-    targets = [":mylib_test", ":mylib", ],
+    targets = [
+        # it's significant that `mylib` goes before `mylib_test`.
+        ":mylib",
+        ":mylib_test",
+    ],
 )
 
 rust_test(
diff --git a/test/rust_analyzer/merging_crates_test/rust_project_json_test.rs b/test/rust_analyzer/merging_crates_test/rust_project_json_test.rs
index c57e01c7ab..2be7caa0ae 100644
--- a/test/rust_analyzer/merging_crates_test/rust_project_json_test.rs
+++ b/test/rust_analyzer/merging_crates_test/rust_project_json_test.rs
@@ -12,10 +12,8 @@ mod tests {
         let content = std::fs::read_to_string(&rust_project_path)
             .expect(&format!("couldn't open {:?}", &rust_project_path));
 
-        for dep in &["lib_dep","", "extra_test_dep"] {
-            if !content.contains(dep) {
-                panic!("expected rust-project.json to contain {}.", dep);
-            }
-        }
+        assert!(
+            content.contains(r#""root_module":"test/rust_analyzer/merging_crates_test/mylib.rs","deps":[{"crate":0,"name":"lib_dep"},{"crate":2,"name":"extra_test_dep"}]"#),
+            "expected rust-project.json to contain both lib_dep and extra_test_dep in deps of mylib.rs.");
     }
 }
diff --git a/test/rust_analyzer/merging_crates_test_reversed/BUILD.bazel b/test/rust_analyzer/merging_crates_test_reversed/BUILD.bazel
new file mode 100644
index 0000000000..8cdd7f567d
--- /dev/null
+++ b/test/rust_analyzer/merging_crates_test_reversed/BUILD.bazel
@@ -0,0 +1,41 @@
+load("//rust:defs.bzl", "rust_analyzer", "rust_library", "rust_test")
+
+rust_library(
+    name = "mylib",
+    srcs = ["mylib.rs"],
+    deps = [":lib_dep"],
+)
+
+rust_library(
+    name = "lib_dep",
+    srcs = ["lib_dep.rs"],
+)
+
+rust_test(
+    name = "mylib_test",
+    crate = ":mylib",
+    deps = [":extra_test_dep"],
+)
+
+rust_library(
+    name = "extra_test_dep",
+    srcs = ["extra_test_dep.rs"],
+)
+
+rust_analyzer(
+    name = "rust_analyzer",
+    testonly = True,
+    targets = [
+        # it's significant that `mylib_test` goes before `mylib`.
+        ":mylib_test",
+        ":mylib",
+    ],
+)
+
+rust_test(
+    name = "rust_project_json_test",
+    srcs = ["rust_project_json_test.rs"],
+    data = [":rust-project.json"],
+    edition = "2018",
+    deps = ["//tools/runfiles"],
+)
diff --git a/test/rust_analyzer/merging_crates_test_reversed/extra_test_dep.rs b/test/rust_analyzer/merging_crates_test_reversed/extra_test_dep.rs
new file mode 100644
index 0000000000..8b13789179
--- /dev/null
+++ b/test/rust_analyzer/merging_crates_test_reversed/extra_test_dep.rs
@@ -0,0 +1 @@
+
diff --git a/test/rust_analyzer/merging_crates_test_reversed/lib_dep.rs b/test/rust_analyzer/merging_crates_test_reversed/lib_dep.rs
new file mode 100644
index 0000000000..8b13789179
--- /dev/null
+++ b/test/rust_analyzer/merging_crates_test_reversed/lib_dep.rs
@@ -0,0 +1 @@
+
diff --git a/test/rust_analyzer/merging_crates_test_reversed/mylib.rs b/test/rust_analyzer/merging_crates_test_reversed/mylib.rs
new file mode 100644
index 0000000000..8b13789179
--- /dev/null
+++ b/test/rust_analyzer/merging_crates_test_reversed/mylib.rs
@@ -0,0 +1 @@
+
diff --git a/test/rust_analyzer/merging_crates_test_reversed/rust_project_json_test.rs b/test/rust_analyzer/merging_crates_test_reversed/rust_project_json_test.rs
new file mode 100644
index 0000000000..dc5d71975a
--- /dev/null
+++ b/test/rust_analyzer/merging_crates_test_reversed/rust_project_json_test.rs
@@ -0,0 +1,19 @@
+use runfiles::Runfiles;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_deps_of_crate_and_its_test_are_merged() {
+        let r = Runfiles::create().unwrap();
+        let rust_project_path = r.rlocation("rules_rust/test/rust_analyzer/merging_crates_test_reversed/rust-project.json");
+
+        let content = std::fs::read_to_string(&rust_project_path)
+            .expect(&format!("couldn't open {:?}", &rust_project_path));
+
+        assert!(
+            content.contains(r#""root_module":"test/rust_analyzer/merging_crates_test_reversed/mylib.rs","deps":[{"crate":0,"name":"lib_dep"},{"crate":1,"name":"extra_test_dep"}]"#),
+            "expected rust-project.json to contain both lib_dep and extra_test_dep in deps of mylib.rs.");
+    }
+}

From d82fe4a6b1fbf83b537d9634b32214f363c1f1b9 Mon Sep 17 00:00:00 2001
From: Marcel Hlopko <hlopko@google.com>
Date: Tue, 22 Jun 2021 09:25:58 +0200
Subject: [PATCH 3/8] Rustfmt

---
 .../aspect_traversal_test/rust_project_json_test.rs           | 3 ++-
 .../merging_crates_test/rust_project_json_test.rs             | 3 ++-
 .../merging_crates_test_reversed/rust_project_json_test.rs    | 4 +++-
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/test/rust_analyzer/aspect_traversal_test/rust_project_json_test.rs b/test/rust_analyzer/aspect_traversal_test/rust_project_json_test.rs
index 2dbe59a2d4..731e2c6cbc 100644
--- a/test/rust_analyzer/aspect_traversal_test/rust_project_json_test.rs
+++ b/test/rust_analyzer/aspect_traversal_test/rust_project_json_test.rs
@@ -2,7 +2,8 @@ use runfiles::Runfiles;
 
 fn main() {
     let r = Runfiles::create().unwrap();
-    let rust_project_path = r.rlocation("rules_rust/test/rust_analyzer/aspect_traversal_test/rust-project.json");
+    let rust_project_path =
+        r.rlocation("rules_rust/test/rust_analyzer/aspect_traversal_test/rust-project.json");
 
     let content = std::fs::read_to_string(&rust_project_path)
         .expect(&format!("couldn't open {:?}", &rust_project_path));
diff --git a/test/rust_analyzer/merging_crates_test/rust_project_json_test.rs b/test/rust_analyzer/merging_crates_test/rust_project_json_test.rs
index 2be7caa0ae..fdb7be91e8 100644
--- a/test/rust_analyzer/merging_crates_test/rust_project_json_test.rs
+++ b/test/rust_analyzer/merging_crates_test/rust_project_json_test.rs
@@ -7,7 +7,8 @@ mod tests {
     #[test]
     fn test_deps_of_crate_and_its_test_are_merged() {
         let r = Runfiles::create().unwrap();
-        let rust_project_path = r.rlocation("rules_rust/test/rust_analyzer/merging_crates_test/rust-project.json");
+        let rust_project_path =
+            r.rlocation("rules_rust/test/rust_analyzer/merging_crates_test/rust-project.json");
 
         let content = std::fs::read_to_string(&rust_project_path)
             .expect(&format!("couldn't open {:?}", &rust_project_path));
diff --git a/test/rust_analyzer/merging_crates_test_reversed/rust_project_json_test.rs b/test/rust_analyzer/merging_crates_test_reversed/rust_project_json_test.rs
index dc5d71975a..036b8160be 100644
--- a/test/rust_analyzer/merging_crates_test_reversed/rust_project_json_test.rs
+++ b/test/rust_analyzer/merging_crates_test_reversed/rust_project_json_test.rs
@@ -7,7 +7,9 @@ mod tests {
     #[test]
     fn test_deps_of_crate_and_its_test_are_merged() {
         let r = Runfiles::create().unwrap();
-        let rust_project_path = r.rlocation("rules_rust/test/rust_analyzer/merging_crates_test_reversed/rust-project.json");
+        let rust_project_path = r.rlocation(
+            "rules_rust/test/rust_analyzer/merging_crates_test_reversed/rust-project.json",
+        );
 
         let content = std::fs::read_to_string(&rust_project_path)
             .expect(&format!("couldn't open {:?}", &rust_project_path));

From 31c06d8bc5c07ba5e8c0eac689ced35115bf41f1 Mon Sep 17 00:00:00 2001
From: Marcel Hlopko <hlopko@google.com>
Date: Tue, 22 Jun 2021 09:33:10 +0200
Subject: [PATCH 4/8] Fix docs

---
 docs/BUILD.bazel | 1 +
 1 file changed, 1 insertion(+)

diff --git a/docs/BUILD.bazel b/docs/BUILD.bazel
index acb3adedfb..3bc1028b9c 100644
--- a/docs/BUILD.bazel
+++ b/docs/BUILD.bazel
@@ -12,6 +12,7 @@ bzl_library(
     ],
     deps = [
         "@rules_proto//proto:rules",
+        "@bazel_skylib//lib:collections",
     ],
 )
 

From be8413c2efcd78a5199caf9865d1d53997ac2a89 Mon Sep 17 00:00:00 2001
From: Marcel Hlopko <hlopko@google.com>
Date: Tue, 22 Jun 2021 09:34:43 +0200
Subject: [PATCH 5/8] Fix buildifier

---
 docs/BUILD.bazel | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/BUILD.bazel b/docs/BUILD.bazel
index 3bc1028b9c..b7f452d1eb 100644
--- a/docs/BUILD.bazel
+++ b/docs/BUILD.bazel
@@ -11,8 +11,8 @@ bzl_library(
         "@build_bazel_rules_nodejs//internal/providers:bzl",
     ],
     deps = [
-        "@rules_proto//proto:rules",
         "@bazel_skylib//lib:collections",
+        "@rules_proto//proto:rules",
     ],
 )
 

From ea1b97e0667f1331c1e0ff6d1a0d512bdf18b24b Mon Sep 17 00:00:00 2001
From: Marcel Hlopko <hlopko@google.com>
Date: Wed, 23 Jun 2021 09:25:38 +0200
Subject: [PATCH 6/8] Remove DepRefInfo

---
 rust/private/rust_analyzer.bzl | 26 +++++++++-----------------
 1 file changed, 9 insertions(+), 17 deletions(-)

diff --git a/rust/private/rust_analyzer.bzl b/rust/private/rust_analyzer.bzl
index 943557161a..10bc7590fd 100644
--- a/rust/private/rust_analyzer.bzl
+++ b/rust/private/rust_analyzer.bzl
@@ -118,14 +118,6 @@ def _crate_id(crate_info):
     """
     return "ID-" + crate_info.root.path
 
-_DepRefInfo = provider(
-    doc = "RustAnalyzerInfo holds rust crate metadata for targets",
-    fields = {
-        "crate": "BuildInfo: build info for this crate if present",
-        "name": "List[String]: features or other compilation --cfg settings",
-    },
-)
-
 def _create_crate(ctx, infos, crate_mapping):
     """Creates a crate in the rust-project.json format.
 
@@ -177,16 +169,16 @@ def _create_crate(ctx, infos, crate_mapping):
         }
     crate["env"].update(canonical_info.env)
 
-    duplicated_deps = []
-    for info in infos:
-        for dep in info.deps:
-            if dep.crate.name == crate_name:
-                continue
-            duplicated_deps.append(_DepRefInfo(crate = crate_mapping[_crate_id(dep.crate)], name = dep.crate.name))
-
-    deps = [{"crate": d.crate, "name": d.name} for d in collections.uniq(duplicated_deps)]
+    # Collect deduplicated pairs of (crate idx from crate_mapping, crate name).
+    # Using dict because we don't have sets in Starlark.
+    deps = {
+        (crate_mapping[_crate_id(dep.crate)], dep.crate.name): None
+        for info in infos
+        for dep in info.deps
+        if dep.crate.name != crate_name
+    }.keys()
 
-    crate["deps"] = deps
+    crate["deps"] = [{"crate": d[0], "name": d[1]} for d in deps]
     crate["cfg"] = canonical_info.cfgs
     crate["target"] = find_toolchain(ctx).target_triple
     if canonical_info.proc_macro_dylib_path != None:

From 66fdc90a166c72e8d242c14443a1e3c22ad3054a Mon Sep 17 00:00:00 2001
From: Marcel Hlopko <hlopko@google.com>
Date: Wed, 23 Jun 2021 09:28:01 +0200
Subject: [PATCH 7/8] Regenerate documentation

---
 docs/BUILD.bazel               | 1 -
 rust/private/rust_analyzer.bzl | 1 -
 2 files changed, 2 deletions(-)

diff --git a/docs/BUILD.bazel b/docs/BUILD.bazel
index b7f452d1eb..acb3adedfb 100644
--- a/docs/BUILD.bazel
+++ b/docs/BUILD.bazel
@@ -11,7 +11,6 @@ bzl_library(
         "@build_bazel_rules_nodejs//internal/providers:bzl",
     ],
     deps = [
-        "@bazel_skylib//lib:collections",
         "@rules_proto//proto:rules",
     ],
 )
diff --git a/rust/private/rust_analyzer.bzl b/rust/private/rust_analyzer.bzl
index 10bc7590fd..a6e5b2e936 100644
--- a/rust/private/rust_analyzer.bzl
+++ b/rust/private/rust_analyzer.bzl
@@ -20,7 +20,6 @@ given targets. This file can be consumed by rust-analyzer as an alternative
 to Cargo.toml files.
 """
 
-load("@bazel_skylib//lib:collections.bzl", "collections")
 load("//rust/platform:triple_mappings.bzl", "system_to_dylib_ext", "triple_to_system")
 load("//rust/private:common.bzl", "rust_common")
 load("//rust/private:rustc.bzl", "BuildInfo")

From bdb7f54019f8549e1656172c3398fb3c2d573026 Mon Sep 17 00:00:00 2001
From: Marcel Hlopko <hlopko@google.com>
Date: Wed, 23 Jun 2021 09:33:24 +0200
Subject: [PATCH 8/8] Defense!

---
 rust/private/rust_analyzer.bzl | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/rust/private/rust_analyzer.bzl b/rust/private/rust_analyzer.bzl
index a6e5b2e936..ea1b7c6433 100644
--- a/rust/private/rust_analyzer.bzl
+++ b/rust/private/rust_analyzer.bzl
@@ -138,6 +138,8 @@ def _create_crate(ctx, infos, crate_mapping):
     Returns:
         (dict) The crate rust-project.json representation
     """
+    if len(infos) == 0:
+        fail("Expected to receive at least one crate to serialize to json, got 0.")
     canonical_info = infos[0]
     crate_name = canonical_info.crate.name
     crate = dict()