Make Cargo.lock overwrite optional (#3526)

Progress towards #3522

Author: illicitonion

crate_universe/extensions.bzl

@@ -558,6 +558,7 @@ def _generate_hub_and_spokes(
         render_config,
         splicing_config,
         lockfile,
+        skip_cargo_lockfile_overwrite,
         cargo_lockfile = None,
         manifests = {},
         packages = {}):
@@ -571,6 +572,9 @@ def _generate_hub_and_spokes(
         render_config (dict): The render config to use.
         splicing_config (dict): The splicing config to use.
         lockfile (path): The path to the crate_universe lock file, if one was provided.
+        skip_cargo_lockfile_overwrite (bool): Whether to skip writing the cargo lockfile back after resolving.
+            You may want to set this if your dependency versions are maintained externally through a non-trivial set-up.
+            But you probably don't want to set this.
         cargo_lockfile (path): Path to Cargo.lock, if we have one.
         manifests (dict): The set of Cargo.toml manifests that apply to this closure, if any, keyed by path.
         packages (dict): The set of extra cargo crate tags that apply to this closure, if any, keyed by package name.
@@ -672,6 +676,7 @@ def _generate_hub_and_spokes(
         nonhermetic_root_bazel_workspace_dir = nonhermetic_root_bazel_workspace_dir,
         paths_to_track_file = paths_to_track_file,
         warnings_output_file = warnings_output_file,
+        skip_cargo_lockfile_overwrite = skip_cargo_lockfile_overwrite,
         **kwargs
     )
 
@@ -1018,6 +1023,7 @@ def _crate_impl(module_ctx):
                 splicing_config = splicing_config,
                 manifests = manifests,
                 packages = packages,
+                skip_cargo_lockfile_overwrite = cfg.skip_cargo_lockfile_overwrite,
             )
 
     metadata_kwargs = {}
@@ -1051,6 +1057,14 @@ _FROM_COMMON_ATTRS = {
             "If set, this file must exist within the workspace (but can be empty) before this rule will work."
         ),
     ),
+    "skip_cargo_lockfile_overwrite": attr.bool(
+        doc = (
+            "Whether to skip writing the cargo lockfile back after resolving. " +
+            "You may want to set this if your dependency versions are maintained externally through a non-trivial set-up. " +
+            "But you probably don't want to set this."
+        ),
+        default = False,
+    ),
     "supported_platform_triples": attr.string_list(
         doc = "A set of all platform triples to consider when generating dependencies.",
         default = SUPPORTED_PLATFORM_TRIPLES,

crate_universe/private/crates_repository.bzl

@@ -112,6 +112,7 @@ def _crates_repository_impl(repository_ctx):
         nonhermetic_root_bazel_workspace_dir = repository_ctx.workspace_root,
         paths_to_track_file = paths_to_track_file,
         warnings_output_file = warnings_output_file,
+        skip_cargo_lockfile_overwrite = repository_ctx.attr.skip_cargo_lockfile_overwrite,
         # sysroot = tools.sysroot,
         **kwargs
     )
@@ -354,6 +355,14 @@ CARGO_BAZEL_REPIN=1 CARGO_BAZEL_REPIN_ONLY=crate_index bazel sync --only=crate_i
             doc = "The version of Rust the currently registered toolchain is using. Eg. `1.56.0`, or `nightly/2021-09-08`",
             default = rust_common.default_version,
         ),
+        "skip_cargo_lockfile_overwrite": attr.bool(
+            doc = (
+                "Whether to skip writing the cargo lockfile back after resolving. " +
+                "You may want to set this if your dependency versions are maintained externally through a non-trivial set-up. " +
+                "But you probably don't want to set this."
+            ),
+            default = False,
+        ),
         "splicing_config": attr.string(
             doc = (
                 "The configuration flags to use for splicing Cargo maniests. Use `//crate_universe:defs.bzl\\%rsplicing_config` to " +

crate_universe/private/generate_utils.bzl

@@ -438,6 +438,7 @@ def execute_generator(
         nonhermetic_root_bazel_workspace_dir,
         paths_to_track_file,
         warnings_output_file,
+        skip_cargo_lockfile_overwrite,
         metadata = None,
         generator_label = None):
     """Execute the `cargo-bazel` binary to produce `BUILD` and `.bzl` files.
@@ -452,6 +453,9 @@ def execute_generator(
         nonhermetic_root_bazel_workspace_dir (path): The path to the current workspace root
         paths_to_track_file (path): Path to file where generator should write which files should trigger re-generating as a JSON list.
         warnings_output_file (path): Path to file where generator should write warnings to print.
+        skip_cargo_lockfile_overwrite (bool): Whether to skip writing the cargo lockfile back after resolving.
+            You may want to set this if your dependency versions are maintained externally through a non-trivial set-up.
+            But you probably don't want to set this.
         generator_label (Label): The label of the `generator` parameter.
         metadata (path, optional): The path to a Cargo metadata json file. If this is set, it indicates to
             the generator that repinning is required. This file must be adjacent to a `Cargo.toml` and
@@ -490,6 +494,11 @@ def execute_generator(
             lockfile_path,
         ])
 
+    if skip_cargo_lockfile_overwrite:
+        args.extend([
+            "--skip-cargo-lockfile-overwrite",
+        ])
+
     # Some components are not required unless re-pinning is enabled
     if metadata:
         args.extend([

crate_universe/src/cli/generate.rs

@@ -96,6 +96,12 @@ pub struct GenerateOptions {
     /// so this provides a way for the repository rule to force printing.
     #[clap(long)]
     pub warnings_output_path: PathBuf,
+
+    /// Whether to skip writing the cargo lockfile back after resolving.
+    /// You may want to set this if your dependency versions are maintained externally through a non-trivial set-up.
+    /// But you probably don't want to set this.
+    #[clap(long)]
+    pub skip_cargo_lockfile_overwrite: bool,
 }
 
 pub fn generate(opt: GenerateOptions) -> Result<()> {
@@ -213,7 +219,9 @@ pub fn generate(opt: GenerateOptions) -> Result<()> {
         write_lockfile(lock_content, &lockfile, opt.dry_run)?;
     }
 
-    update_cargo_lockfile(&opt.cargo_lockfile, cargo_lockfile)?;
+    if !opt.skip_cargo_lockfile_overwrite {
+        update_cargo_lockfile(&opt.cargo_lockfile, cargo_lockfile)?;
+    }
 
     Ok(())
 }