rustdoc_test: substitute the root of the current crate (bazelbuild#1777)

Otherwise a trivial little crate with no rust_library dependencies, and
a build script dependency, fails. This is unusual because most crates
complex enough to have a build script also have other dependencies, I
ran into while minimizing a test case for another bug.

rust/private/rustdoc_test.bzl

@@ -64,6 +64,9 @@ def _construct_writer_arguments(ctx, test_runner, opt_test_params, action, crate
     # Collect and dedupe all of the file roots in a list before appending
     # them to args to prevent generating a large amount of identical args
     roots = []
+    root = crate_info.output.root.path
+    if not root in roots:
+        roots.append(root)
     for dep in crate_info.deps.to_list():
         dep_crate_info = getattr(dep, "crate_info", None)
         dep_dep_info = getattr(dep, "dep_info", None)

test/unit/rustdoc/rustdoc_build.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("cargo:rustc-env=CONST=xyz");
+}

test/unit/rustdoc/rustdoc_lib.rs

@@ -4,6 +4,9 @@ use rustdoc_proc_macro::make_answer;
 #[cfg(feature = "with_proc_macro")]
 make_answer!();
 
+#[cfg(feature = "with_build_script")]
+pub const CONST: &str = env!("CONST");
+
 /// The answer to the ultimate question
 /// ```
 /// fn answer() -> u32 { 42 }

test/unit/rustdoc/rustdoc_nodep_lib.rs

@@ -0,0 +1,28 @@
+#[cfg(feature = "with_proc_macro")]
+use rustdoc_proc_macro::make_answer;
+
+#[cfg(feature = "with_proc_macro")]
+make_answer!();
+
+#[cfg(feature = "with_build_script")]
+pub const CONST: &str = env!("CONST");
+
+/// The answer to the ultimate question
+/// ```
+/// fn answer() -> u32 { 42 }
+/// assert_eq!(answer(), 42);
+/// ```
+#[cfg(not(feature = "with_proc_macro"))]
+pub fn answer() -> u32 {
+    42
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_answer() {
+        assert_eq!(answer(), 42);
+    }
+}

test/unit/rustdoc/rustdoc_unit_test.bzl

@@ -2,6 +2,7 @@
 
 load("@bazel_skylib//lib:unittest.bzl", "analysistest")
 load("@rules_cc//cc:defs.bzl", "cc_library")
+load("//cargo:defs.bzl", "cargo_build_script")
 load("//rust:defs.bzl", "rust_binary", "rust_doc", "rust_doc_test", "rust_library", "rust_proc_macro", "rust_test")
 load(
     "//test/unit:common.bzl",
@@ -118,6 +119,12 @@ def _define_targets():
         rustdoc_deps = [":adder"],
     )
 
+    _target_maker(
+        rust_library,
+        name = "nodep_lib",
+        srcs = ["rustdoc_nodep_lib.rs"],
+    )
+
     _target_maker(
         rust_proc_macro,
         name = "rustdoc_proc_macro",
@@ -133,6 +140,14 @@ def _define_targets():
         crate_features = ["with_proc_macro"],
     )
 
+    _target_maker(
+        rust_library,
+        name = "lib_nodep_with_proc_macro",
+        srcs = ["rustdoc_nodep_lib.rs"],
+        proc_macro_deps = [":rustdoc_proc_macro"],
+        crate_features = ["with_proc_macro"],
+    )
+
     _target_maker(
         rust_binary,
         name = "bin_with_transitive_proc_macro",
@@ -157,6 +172,37 @@ def _define_targets():
         deps = [":cc_lib"],
     )
 
+    _target_maker(
+        rust_library,
+        name = "lib_nodep_with_cc",
+        srcs = ["rustdoc_nodep_lib.rs"],
+        crate_features = ["with_cc"],
+        deps = [":cc_lib"],
+    )
+
+    cargo_build_script(
+        name = "lib_build_script",
+        srcs = ["rustdoc_build.rs"],
+        edition = "2018",
+    )
+
+    _target_maker(
+        rust_library,
+        name = "lib_with_build_script",
+        srcs = ["rustdoc_lib.rs"],
+        rustdoc_deps = [":adder"],
+        crate_features = ["with_build_script"],
+        deps = [":lib_build_script"],
+    )
+
+    _target_maker(
+        rust_library,
+        name = "lib_nodep_with_build_script",
+        srcs = ["rustdoc_nodep_lib.rs"],
+        crate_features = ["with_build_script"],
+        deps = [":lib_build_script"],
+    )
+
 def rustdoc_test_suite(name):
     """Entry-point macro called from the BUILD file.