compile_data does not work together with generated sources

[martingms]

When using generated srcs and non-generated compile_data in the same rust_library target, the non-generated srcs are symlinked into the out-tree for the build, but the same is not done for non-generated compile_data, so the files are not available for include_str! or whatever.

Here's a patch that reproduces this within the existing compile_data tests:

diff --git a/test/unit/compile_data/compile_data.rs b/test/unit/compile_data/compile_data.rs
index 26f060e0..ddc8fabd 100644
--- a/test/unit/compile_data/compile_data.rs
+++ b/test/unit/compile_data/compile_data.rs
@@ -1,6 +1,8 @@
 /// Data loaded from compile data
 pub const COMPILE_DATA: &str = include_str!("compile_data.txt");
 
+mod generated;
+
 #[cfg(test)]
 mod test {
     use super::*;
@@ -23,4 +25,9 @@ mod test {
             assert_eq!(TEST_COMPILE_DATA.trim_end(), "test compile data contents");
         }
     }
+
+    #[test]
+    fn test_generated() {
+        assert_eq!(generated::GENERATED, "generated");
+    }
 }
diff --git a/test/unit/compile_data/compile_data_test.bzl b/test/unit/compile_data/compile_data_test.bzl
index cd0eb7f2..383ea65c 100644
--- a/test/unit/compile_data/compile_data_test.bzl
+++ b/test/unit/compile_data/compile_data_test.bzl
@@ -61,9 +61,15 @@ wrapper_rule_propagates_and_joins_compile_data_test = analysistest.make(_wrapper
 compile_data_propagates_to_rust_doc_test = analysistest.make(_compile_data_propagates_to_rust_doc_test_impl)
 
 def _define_test_targets():
+    native.genrule(
+        name = "generated_src",
+        outs = ["generated.rs"],
+        cmd = """echo 'const GENERATED: &str = "generated";' > $@""",
+    )
+
     rust_library(
         name = "compile_data",
-        srcs = ["compile_data.rs"],
+        srcs = ["compile_data.rs", ":generated.rs"],
         compile_data = ["compile_data.txt"],
         edition = "2018",
     )

This is possible to work around by using genrule or similar to copy the files in compile_data to make it "generated", but this does not seem ideal.