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[docs] Add module build related definitions to Lexicon. #32153

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[docs] Add module build related definitions to Lexicon. #32153

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30 changes: 30 additions & 0 deletions docs/Lexicon.md
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Expand Up @@ -162,6 +162,25 @@ written "dupe". Pronounced the same way as the first syllable of
A value whose type is a protocol composition (including a single protocol
and *zero* protocols; the latter is the `Any` type).

## explicit module build

A module build where all dependency modules (including Clang modules) are
passed to the compiler explicitly by an external build system, including
any modules in caches. See also: [implicit module build](#implicit-module-build)
and [fast dependency scanner](#fast-dependency-scanner).

## fast dependency scanner

A Swift compiler mode that scans a Swift module for import declarations and
resolves which modules will be loaded. It is based on the
[clang-scan-deps](https://llvm.org/devmtg/2019-04/slides/TechTalk-Lorenz-clang-scan-deps_Fast_dependency_scanning_for_explicit_modules.pdf)
library within Clang, for (Objective-)C modules, but is extended to also
understand textual Swift modules (.swiftinterface files).
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It may worth mentioning swift-driver provides APIs to digest the output of the scanner. This is to allow build systems to share more module building logics.


The fast dependency scanner outputs a graph of compilation steps which can be
used by a build system to schedule
[explicit module builds](#explicit-module-builds).

## fragile

Describes a type or function where making changes will break binary
Expand Down Expand Up @@ -193,6 +212,17 @@ compared directly.

["if and only if"](https://en.wikipedia.org/wiki/If_and_only_if). This term comes from mathematics.

## implicit module build

A module build where the compiler is free to transparently build dependent
modules (including Clang modules), and access modules in different caches as
necessary. For example, if a textual Swift module (.swiftinterface file) for
a dependency does not have a corresponding binary Swift module (.swiftmodulea
file), the compiler may transparently build a binary Swift module from the
textual one as a cache for future compiler jobs, without involving any external
build system that invoked the compiler. See also:
[explicit module build](#explicit-module-build).
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Please also mention the shortcomings of implicit module builds: because build systems have no way to control when and where these modules are built, sharing modules among different nodes for distributed build systems can be difficult.


## interface type

The type of a value or declaration outside its generic context. These types
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