Swift library is getting invalidated and recompiled when private headers change in Objective-C dependency

[ivan-golub]

Likely coming from

rules_swift/swift/toolchains/config/compile_config.bzl

Line 1450 in 69df972

transitive_inputs.append(compilation_context.headers)

includes all private and public transitive headers.

Running bazel aquery "deps(//examples/apple/objc_interop:Printer)" confirms Private.h header that is in srcs (ie private) is part of inputs of Compiling Swift module //examples/apple/objc_interop:Printer action

action 'Compiling Swift module //examples/apple/objc_interop:Printer'
  Mnemonic: SwiftCompile
  Target: //examples/apple/objc_interop:Printer
  Configuration: darwin_arm64-fastbuild
  Execution platform: @platforms//host:host
  ActionKey: f65865cb7a00d8996f036bcd31777ff98e6e2ac928c348fdd6fa8c89dd1dfb2e
  Inputs: [bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/PrintStream_modulemap/_/module.modulemap, bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/Printer.output_file_map.json, bazel-out/darwin_arm64-opt-exec-ST-d57f47055a04/bin/tools/worker/worker, bazel-out/darwin_arm64-opt-exec-ST-d57f47055a04/internal/_middlemen/tools_Sworker_Sworker-runfiles, examples/apple/objc_interop/OIPrintStream.h, examples/apple/objc_interop/Printer.swift, examples/apple/objc_interop/Private.h, swift/toolchains/config/const_protocols_to_gather.json]
  Outputs: [bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/Printer.macro-expansions (TreeArtifact), bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/Printer_objs/Printer.swift.o, bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/Printer_objs/Printer.swift.swiftconstvalues, bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/examples_apple_objc_interop_Printer.swiftdoc, bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/examples_apple_objc_interop_Printer.swiftmodule, bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/examples_apple_objc_interop_Printer.swiftsourceinfo, bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/generated_header/Printer-Swift.h]
  Environment: [APPLE_SDK_PLATFORM=MacOSX, APPLE_SDK_VERSION_OVERRIDE=14.0, PATH=/bin:/usr/bin:/usr/local/bin, XCODE_VERSION_OVERRIDE=15.0.0.15A240d]
  Command Line: (exec bazel-out/darwin_arm64-opt-exec-ST-d57f47055a04/bin/tools/worker/worker \
    swiftc \
    -target \
    arm64-apple-macos13.0 \
    -sdk \
    __BAZEL_XCODE_SDKROOT__ \
    -debug-prefix-map \
    '__BAZEL_XCODE_DEVELOPER_DIR__=/PLACEHOLDER_DEVELOPER_DIR' \
    -file-prefix-map \
    '__BAZEL_XCODE_DEVELOPER_DIR__=/PLACEHOLDER_DEVELOPER_DIR' \
    '-Xwrapped-swift=-bazel-target-label=@@//examples/apple/objc_interop:Printer' \
    -emit-object \
    -output-file-map \
    bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/Printer.output_file_map.json \
    -Xfrontend \
    -no-clang-module-breadcrumbs \
    -emit-module-path \
    bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/examples_apple_objc_interop_Printer.swiftmodule \
    -emit-objc-header-path \
    bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/generated_header/Printer-Swift.h \
    -emit-const-values-path \
    bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/Printer_objs/Printer.swift.swiftconstvalues \
    -Xfrontend \
    -const-gather-protocols-file \
    -Xfrontend \
    swift/toolchains/config/const_protocols_to_gather.json \
    -DDEBUG \
    -Onone \
    -Xfrontend \
    -no-serialize-debugging-options \
    -enable-testing \
    -gline-tables-only \
    '-Xwrapped-swift=-debug-prefix-pwd-is-dot' \
    '-Xwrapped-swift=-file-prefix-pwd-is-dot' \
    -module-cache-path \
    bazel-out/darwin_arm64-fastbuild/bin/_swift_module_cache \
    '-Xwrapped-swift=-macro-expansion-dir=bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/Printer.macro-expansions' \
    -Xcc \
    -iquote. \
    -Xcc \
    -iquotebazel-out/darwin_arm64-fastbuild/bin \
    -Xcc \
    '-fmodule-map-file=bazel-out/darwin_arm64-fastbuild/bin/examples/apple/objc_interop/PrintStream_modulemap/_/module.modulemap' \
    -Xfrontend \
    -color-diagnostics \
    -enable-batch-mode \
    -module-name \
    examples_apple_objc_interop_Printer \
    -enable-bare-slash-regex \
    -parse-as-library \
    -static \
    -Xcc \
    -O0 \
    -Xcc \
    '-DDEBUG=1' \
    examples/apple/objc_interop/Printer.swift)
# Configuration: ed8e8684eb5cd4576c9547de6ce9b0f2ecde34f2a5ec7d6f3d71fa9ce8a87dbf
# Execution platform: @@platforms//host:host
  ExecutionInfo: {requires-darwin: '', requires-worker-protocol: json, supports-workers: 1, supports-xcode-requirements-set: ''}

Repro: ivan-golub#1