Support rustfmt on crates with generated sources (#2255)

closes https://github.com/bazelbuild/rules_rust/issues/2254

.rustfmt.toml

@@ -0,0 +1,6 @@
+# rustfmt options: https://rust-lang.github.io/rustfmt/
+
+# Skipping children allows rustfmt to run on crates with
+# generated source files. Without this formatting will
+# fail with: `failed to resolve mod ${MOD}`.
+skip_children = true

docs/rust_fmt.md

@@ -46,6 +46,14 @@ file is used whenever `rustfmt` is run:
 build --@rules_rust//:rustfmt.toml=//:rustfmt.toml
 ```
 
+### Tips
+
+
+Any target which uses Bazel generated sources will cause the `@rules_rust//tools/rustfmt` tool to fail with
+``failed to resolve mod `MOD` ``. To avoid failures, [`skip_children = true`](https://rust-lang.github.io/rustfmt/?version=v1.6.0&search=skip_chil#skip_children)
+is recommended to be set in the workspace's `rustfmt.toml` file which allows rustfmt to run on these targets
+without failing.
+
 [rustfmt]: https://github.com/rust-lang/rustfmt#readme
 [rsg]: https://github.com/rust-lang-nursery/fmt-rfcs/blob/master/guide/guide.md
 [rfcp]: https://github.com/rust-lang-nursery/fmt-rfcs

docs/rust_fmt.vm

@@ -38,6 +38,14 @@ file is used whenever `rustfmt` is run:
 ```text
 build --@rules_rust//:rustfmt.toml=//:rustfmt.toml
 ```
+#[[
+### Tips
+]]#
+
+Any target which uses Bazel generated sources will cause the `@rules_rust//tools/rustfmt` tool to fail with
+``failed to resolve mod `MOD` ``. To avoid failures, [`skip_children = true`](https://rust-lang.github.io/rustfmt/?version=v1.6.0&search=skip_chil#skip_children)
+is recommended to be set in the workspace's `rustfmt.toml` file which allows rustfmt to run on these targets
+without failing.
 
 [rustfmt]: https://github.com/rust-lang/rustfmt#readme
 [rsg]: https://github.com/rust-lang-nursery/fmt-rfcs/blob/master/guide/guide.md

test/rustfmt/BUILD.bazel

@@ -1,9 +1,21 @@
+load("@bazel_skylib//rules:write_file.bzl", "write_file")
 load(":rustfmt_integration_test_suite.bzl", "rustfmt_integration_test_suite")
 
 exports_files([
     "test_rustfmt.toml",
 ])
 
+write_file(
+    name = "srcs/generated/generated",
+    out = "srcs/generated/generated.rs",
+    content = """\
+pub fn greeting() {
+    println!("Guten tag!");
+}
+""".splitlines(),
+    newline = "unix",
+)
+
 rustfmt_integration_test_suite(
     name = "rustfmt_integration_test_suite",
 )

test/rustfmt/rustfmt_failure_test.sh

@@ -69,6 +69,7 @@ EOF
     check_build_result $TEST_FAILED ${variant}_unformatted_2018_test
     check_build_result $TEST_OK ${variant}_formatted_2015_test
     check_build_result $TEST_OK ${variant}_formatted_2018_test
+    check_build_result $TEST_OK ${variant}_generated_test
   done
 
   # Format a specific target
@@ -81,6 +82,7 @@ EOF
     check_build_result $TEST_OK ${variant}_unformatted_2018_test
     check_build_result $TEST_OK ${variant}_formatted_2015_test
     check_build_result $TEST_OK ${variant}_formatted_2018_test
+    check_build_result $TEST_OK ${variant}_generated_test
   done
 
   # Format all targets

test/rustfmt/rustfmt_integration_test_suite.bzl

@@ -29,6 +29,9 @@ def rustfmt_integration_test_suite(name, **kwargs):
 
     tests = []
     for variant, rust_rule in _VARIANTS.items():
+        #
+        # Test edition 2018
+        #
         rust_rule(
             name = "{}_formatted_2018".format(variant),
             srcs = ["srcs/2018/formatted.rs"],
@@ -53,6 +56,9 @@ def rustfmt_integration_test_suite(name, **kwargs):
             targets = [":{}_unformatted_2018".format(variant)],
         )
 
+        #
+        # Test edition 2015
+        #
         rust_rule(
             name = "{}_formatted_2015".format(variant),
             srcs = ["srcs/2015/formatted.rs"],
@@ -77,11 +83,30 @@ def rustfmt_integration_test_suite(name, **kwargs):
             targets = [":{}_unformatted_2015".format(variant)],
         )
 
+        #
+        # Test targets with generated sources
+        #
+        rust_rule(
+            name = "{}_generated".format(variant),
+            srcs = [
+                "srcs/generated/lib.rs",
+                "srcs/generated/generated.rs",
+            ],
+            crate_root = "srcs/generated/lib.rs",
+            edition = "2021",
+        )
+
+        rustfmt_test(
+            name = "{}_generated_test".format(variant),
+            targets = [":{}_generated".format(variant)],
+        )
+
         tests.extend([
             "{}_formatted_2015_test".format(variant),
             "{}_formatted_2018_test".format(variant),
             "{}_unformatted_2015_test".format(variant),
             "{}_unformatted_2018_test".format(variant),
+            "{}_generated_test".format(variant),
         ])
 
     native.test_suite(
@@ -93,4 +118,5 @@ def rustfmt_integration_test_suite(name, **kwargs):
     native.sh_binary(
         name = "{}.test_runner".format(name),
         srcs = ["rustfmt_failure_test.sh"],
+        testonly = True,
     )

test/rustfmt/srcs/generated/lib.rs

@@ -0,0 +1,5 @@
+mod generated;
+
+pub fn main() {
+    generated::greeting();
+}

test/rustfmt/test_rustfmt.toml

@@ -1 +1,8 @@
+# rustfmt options: https://rust-lang.github.io/rustfmt/
+
+# Skipping children allows rustfmt to run on crates with
+# generated source files. Without this formatting will
+# fail with: `failed to resolve mod ${MOD}`.
+skip_children = true
+
 reorder_imports = false

tools/rustfmt/rustfmt.toml

@@ -1 +1,6 @@
 # rustfmt options: https://rust-lang.github.io/rustfmt/
+
+# Skipping children allows rustfmt to run on crates with
+# generated source files. Without this formatting will
+# fail with: `failed to resolve mod ${MOD}`.
+skip_children = true