Move clangScanningTool and clangScanningService to be parts of 'ModuleDependenciesCache' state, getting rid of the 'ClangModuleDependenciesCacheImpl', which is no-longer needed since we moved moved to by-name lookup of Clang modules.
This change tweaks the 'GlobalModuleDependenciesCache', which persists across scanner invocations with the same 'DependencyScanningTool' to no longer cache discovered Clang modules.
Doing so felt like a premature optimization, and we should instead attempt to share as much state as possible by keeping around the actual Clang scanner's state, which performs its own caching. Caching discovered dependencies both in the Clang scanner instance, and in our own cache is much more error-prone - the Clang scanner has a richer context for what is okay and not okay to cache/re-use.
Instead, we still cache discovered Clang dependencies *within* a given scan, since those are discovered using a common Clang scanner instance and should be safe to keep for the duration of the scan.
This change should make it simpler to pin down the core functionality and correctness of the scanner.
Once we turn our attention to the scanner's performance, we can revisit this strategy and optimize the caching behaviour.
When we are building a Swift module which has an underlying Clang module, and which generates an ObjC interface ('-Swift.h'), the mechanism for building the latter involves a VFS redirect of its modulemap to one that does not yet have the generated Swift code, because it must be built before the Swift portion is built because the Swift portion depends on it. This means that the invocation to build this module is different to one used by the clients which depend on this module.
To avoid the subsequent client scans from re-using the partial (VFS-redirected) module, ensure that we do not store dependency info of the underlying Clang module into the global scanner cache. This will cause subsequent client scans to re-scan for this module, and find the fully-resolved modulemap without a VFS redirect.
Resolves rdar://88309064
And only resolve cached dependencies that came from scanning actions with the same target triple.
This change means that the `GlobalModuleDependenciesCache` must be configured with a specific target triple for every scannig action, and it will only resolve previously-found dependencies from previous scannig actions using the exact same triple.
Furthermore, the `GlobalModuleDependenciesCache` separately tracks source-file-based module dependencies as those represent main Swift modules of previous scanning actions, and we must be able to resolve those regardless of the target triple.
Resolves rdar://83105455
These kinds of modules differ from `SwiftTextual` modules in that they do not have an interface and have source-files.
It is cleaner to enforce this distinction with types, instead of checking for interface optionality everywhere.
This change causes the cache to be layered with a local "cache" that wraps the global cache, which will serve as the source of truth. The local cache persists only for the duration of a given scanning action, and has a store of references to dependencies resolved as a part of the current scanning action only, while the global cache is the one that persists across scanning actions (e.g. in `DependencyScanningTool`) and stores actual module dependency info values.
Only the local cache can answer dependency lookup queries, checking current scanning action results first, before falling back to querying the global cache, with queries disambiguated by the current scannning action's search paths, ensuring we never resolve a dependency lookup query with a module info that could not be found in the current action's search paths.
This change is required because search-path disambiguation can lead to false-negatives: for example, the Clang dependency scanner may find modules relative to the compiler's path that are not on the compiler's direct search paths. While such false-negative query responses should be functionally safe, we rely on the current scanning action's results being always-present-in-the-cache for the scanner's functionality. This layering ensures that the cache use-sites remain unchanged and that we get both: preserved global state which can be queried disambiguated with the search path details, and an always-consistent local (current action) cache state.
The dependency scanner's cache persists across different queries and answering a subsequent query's module lookup with a module not in the query's search path is not correct.
For example, suppose we are looking for a Swift module `Foo` with a set of search paths `SP`.
And dependency scanner cache already contains a module `Foo`, for which we found an interface file at location `L`. If `L`∉`SP`, then we cannot re-use the cached entry because we’d be resolving the scanning query to a filesystem location that the current scanning context is not aware of.
Resolves rdar://81175942
This matches the behavior of the current client (`swift-driver`) and reduces ambiguity in how the nodes in the graph are to be treated. Swift dependencies with a textual interface, for example, must be built into a binary module by clients. Swift dependencies without a textual interface, with only a binary module, are to be used directly, without any up-to-date checks.
Note, this is distinct from Swift dependencies that have a textual interface, for which we also detect potential pre-build binary module candidates. Those are still reported in the `details` field of textual Swift dependencies as `prebuiltModuleCandidates`.
Annotate the covered switches with `llvm_unreachable` to avoid the MSVC
warning which does not recognise the covered switches. This allows us
to avoid a spew of warnings.
When there is a bridging header associated with the module, scan and record
its dependencies. Note them in a separate structure to capture the specific
dependencies of the bridging header.
Implement a new "fast" dependency scanning option,
`-scan-dependencies`, in the Swift frontend that determines all
of the source file and module dependencies for a given set of
Swift sources. It covers four forms of modules:
1) Swift (serialized) module files, by reading the module header
2) Swift interface files, by parsing the source code to find imports
3) Swift source modules, by parsing the source code to find imports
4) Clang modules, using Clang's fast dependency scanning tool
A single `-scan-dependencies` operation maps out the full
dependency graph for the given Swift source files, including all
of the Swift and Clang modules that may need to be built, such
that all of the work can be scheduled up front by the Swift
driver or any other build system that understands this
option. The dependency graph is emitted as JSON, which can be
consumed by these other tools.
