https://github.com/swiftlang/swift/pull/79270 taught the dependency scanner to ignore `-file-compilation-dir` when caching is
_not_ in effect but did not make the corresponding change when caching is in effect. This PR teaches the scanner to ignore `-file-compliation-dir` when caching is in effect.
rdar://146025100
When the swiftmodule is built with different clang importer arguments,
they can have the same module hash, causing them to be wrongly re-used even
they contains different interfaces. Add ReducedExtraArgs to the module hash to
disambiguate them.
However, some Xcc arguments, most commonly `-D` options do not affect the
swiftmodule being generated. Do not pass `-Xcc -DARGS` to swift
interface compilation to reduce the amount of module variants in the
build.
rdar://131408266
Improve swift dependency scanner by validating and selecting dependency
module into scanner. This provides benefits that:
* Build system does not need to schedule interface compilation task if
the candidate module is picked, it can just use the candidate module
directly.
* There is no need for forwarding module in the explicit module build.
Since the build system is coordinating the build, there is no need for
the forwarding module in the module cache to avoid duplicated work,
* This also correctly supports all the module loading modes in the
dependency scanner.
This is achieved by only adding validate and up-to-date binary module as
the candidate module for swift interface module dependency. This allows
caching build to construct the correct dependency in the CAS. If there
is a candidate module for the interface module, dependency scanner will
return a binary module dependency in the dependency graph.
The legacy behavior is mostly preserved with a hidden frontend flag
`-no-scanner-module-validation`, while the scanner output is mostly
interchangeable with new scanner behavior with `prefer-interface` module
loading mode except the candidate module will not be returned.
rdar://123711823
When caching build is enabled, teach dependency scanner to report
command-lines with `-direct-clang-cc1-module-build` so the later
compilation can instantiate clang importer with cc1 args directly. This
avoids running clang driver code, which might involve file system
lookups, which are the file deps that are not captured and might result
in different compilation mode.
rdar://119275464
