Teach swift dependency scanner to use CAS to capture the full dependencies for a build and construct build commands with immutable inputs from CAS.
This allows swift compilation caching using CAS.
For example, when scanning a source module `Foo`, which, when depending on module `Bar` causes a cross-import overlay `_Foo_Bar` to be added, do not add this cross-import overlay when scanning `Foo` itself. For example, if `Foo` adds a dependency on `Bar` itself in its own dependency graph.
This changes the scanner's behavior to "resolve" a discovered module's dependencies to a set of Module IDs: module name + module kind (swift textual, swift binary, clang, etc.).
The 'ModuleDependencyInfo' objects that are stored in the dependency scanner's cache now carry a set of kind-qualified ModuleIDs for their dependencies, in addition to unqualified imported module names of their dependencies.
Previously, the scanner's internal state would cache a module dependnecy as having its own set of dependencies which were stored as names of imported modules. This led to a design where any time we needed to process the dependency downstream from its discovery (e.g. cycle detection, graph construction), we had to query the ASTContext to resolve this dependency's imports, which shouldn't be necessary. Now, upon discovery, we "resolve" a discovered dependency by executing a lookup for each of its imported module names (this operation happens regardless of this patch) and store a fully-resolved set of dependencies in the dependency module info.
Moreover, looking up a given module dependency by name (via `ASTContext`'s `getModuleDependencies`) would result in iterating over the scanner's module "loaders" and querying each for the module name. The corresponding modules would then check the scanner's cache for a respective discovered module, and if no such module is found the "loader" would search the filesystem.
This meant that in practice, we searched the filesystem on many occasions where we actually had cached the required dependency, as follows:
Suppose we had previously discovered a Clang module "foo" and cached its dependency info.
-> ASTContext.getModuleDependencies("foo")
--> (1) Swift Module "Loader" checks caches for a Swift module "foo" and doesn't find one, so it searches the filesystem for "foo" and fails to find one.
--> (2) Clang Module "Loader" checks caches for a Clang module "foo", finds one and returns it to the client.
This means that we were always searching the filesystem in (1) even if we knew that to be futile.
With this change, queries to `ASTContext`'s `getModuleDependencies` will always check all the caches first, and only delegate to the scanner "loaders" if no cached dependency is found. The loaders are then no longer in the business of checking the cached contents.
To handle cases in the scanner where we must only lookup either a Swift-only module or a Clang-only module, this patch splits 'getModuleDependencies' into an alrady-existing 'getSwiftModuleDependencies' and a newly-added 'getClangModuleDependencies'.
`getValue` -> `value`
`getValueOr` -> `value_or`
`hasValue` -> `has_value`
`map` -> `transform`
The old API will be deprecated in the rebranch.
To avoid merge conflicts, use the new API already in the main branch.
rdar://102362022
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.
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.
The FileCollectorBase is the common interface shared by different
implementations. In lldb, we implement our own lazy variant that allows
us to do the heavy lifting out-of-process instead of inside the signal
handler.
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`.
Also perform the plumbing necessary to convince the rest of the compiler that they're just ordinary external dependencies. In particular, we will still emit these depenencies into .d files, and code completion will still index them.
Expand the FrontendOptions to allow the enabling
of the dependency tracker for non-system
dependencies, and switch the previous clients of
`createDependencyTracker` over to using this
option. This ensures that the dependency tracker
is now set only during `CompilerInstance::setup`.
For reproducers in LLDB, we need to collect module dependency
information coming from the clang importer. However, we cannot override
the dependency collector, like we do in LLDB, because its interface is
completely hidden in the clang importer. The solution is to pass the
FileCollector through the DependencyTracker.
(cherry picked from commit c624a87bd5)
