Enable semanticdb phase during plugin bootstrapping (#1830)

* Enable semanticdb phase during plugin bootstrapping

scala_library_for_plugin_bootstrapping skipped phase_semanticdb, so
when a toolchain sets enable_semanticdb=True and includes a
-P:semanticdb:... scalacopt (e.g. -P:semanticdb:synthetics:on), the
bootstrap compilation of the dep analyzer plugin received the flag but
had no semanticdb plugin loaded, causing scalac to fail with
"bad option: -P:semanticdb:synthetics:on".

Unconditionally run phase_semanticdb in the bootstrap phase list so the
plugin jar is loaded whenever the toolchain enables semanticdb.

Adds a regression test that builds with a synthetics-enabled semanticdb
toolchain to verify the bootstrap path handles these scalacopts.

Author: thirtyseven

scala/private/rules/scala_library.bzl

@@ -163,7 +163,7 @@ def _scala_library_for_plugin_bootstrapping_impl(ctx):
             ("dependency", phase_dependency_library_for_plugin_bootstrapping),
             ("collect_jars", phase_collect_jars_common),
             ("scalacopts", phase_scalacopts),
-            #("semanticdb", phase_semanticdb), noneed for semanticdb in bootstrap
+            ("semanticdb", phase_semanticdb),  # enable semanticdb during bootstrap since toolchain scalacopts may include flags for it
             ("compile", phase_compile_library_for_plugin_bootstrapping),
             ("merge_jars", phase_merge_jars),
             ("runfiles", phase_runfiles_library),

test/semanticdb/BUILD

@@ -30,6 +30,21 @@ toolchain(
     visibility = ["//visibility:public"],
 )
 
+scala_toolchain(
+    name = "semanticdb_synthetics_toolchain_impl",
+    enable_semanticdb = True,
+    scalacopts = ["-P:semanticdb:synthetics:on"],
+    semanticdb_bundle_in_jar = False,
+    visibility = ["//visibility:public"],
+)
+
+toolchain(
+    name = "semanticdb_synthetics_toolchain",
+    toolchain = ":semanticdb_synthetics_toolchain_impl",
+    toolchain_type = "//scala:toolchain_type",
+    visibility = ["//visibility:public"],
+)
+
 scala_library(
     name = "all_lib",
     srcs = glob(["*.scala"]),

test/shell/test_semanticdb.sh

@@ -177,6 +177,18 @@ test_semanticdb_handles_removed_sourcefiles() {
 
 }
 
+test_semanticdb_synthetics_toolchain_scalaopt() {
+  # Regression test: building with a toolchain that sets enable_semanticdb=True and
+  # includes -P:semanticdb:synthetics:on in scalacopts should succeed. Previously it
+  # failed because scala_library_for_plugin_bootstrapping (which compiles the dep
+  # analyzer plugin) skipped phase_semanticdb, so the semanticdb plugin was never
+  # loaded but the -P:semanticdb:... flag was still forwarded to scalac.
+  set -e
+  bazel build \
+    --extra_toolchains="//test/semanticdb:semanticdb_synthetics_toolchain" \
+    //test/semanticdb:all_lib
+}
+
 run_semanticdb_tests() {
   local bundle=1;   local nobundle=0
   local scala3=3;    local scala2=2
@@ -191,6 +203,7 @@ run_semanticdb_tests() {
 
   $runner test_no_semanticdb
   $runner test_semanticdb_handles_removed_sourcefiles
+  $runner test_semanticdb_synthetics_toolchain_scalaopt
 }
 
 run_semanticdb_tests