Allow user-defined macros to be loaded from dynamic libraries and evaluated.
- Introduce a _CompilerPluginSupport module installed into the toolchain. Its `_CompilerPlugin` protocol acts as a stable interface between the compiler and user-defined macros.
- Introduce a `-load-plugin-library <path>` attribute which allows users to specify dynamic libraries to be loaded into the compiler.
A macro library must declare a public top-level computed property `public var allMacros: [Any.Type]` and be compiled to a dynamic library. The compiler will call the getter of this property to obtain and register all macros.
Known issues:
- We current do not have a way to strip out unnecessary symbols from the plugin dylib, i.e. produce a plugin library that does not contain SwiftSyntax symbols that will collide with the compiler itself.
- `MacroExpansionExpr`'s type is hard-coded as `(Int, String)`. It should instead be specified by the macro via protocol requirements such as `signature` and `genericSignature`. We need more protocol requirements in `_CompilerPlugin` to handle this.
- `dlopen` is not secure and is only for prototyping use here.
Friend PR: apple/swift-syntax#1022
Two paths missed setting up overlays:
- `CompletionInstance` when checking files from dependencies
- `SwiftASTManager` when reading in files that it would later replace
all inputs with
(1) would cause the AST context not to be re-used, even though nothing
had changed. (2) caused all non-completion functionality to fail for any
symbols within files only specified by the overlay.
Resolves rdar://85508213.
The idea behind storing a StringRef was to reduce the memory footprint because we made the assumption that a `ModuleSearchPath` always outlives the `SearchPathOptions` it was created from. What I did not consider was that the path was referencing into a `std::vector`, which could get resized, thus invaliding the memory the `ModuleSearchPath`’s `StringRef` was pointing to, causing memory corruption.
To fix this, store the path string inisde the `ModuleSearchPath` itself. Since we store a `ModuleSearchPath` for every file inside that module search path in the `LookupTable`, by itself this would cause a new copy of the path to be stored for every file inside a module search path. To avoid this, make `ModuleSearchPath` ref counted and only store a reference to one shared `ModuleSearchPath` entry in the lookup table.
rdar://88888679
When looking for a Swift module on disk, we were scanning all module search paths if they contain the module we are searching for. In a setup where each module is contained in its own framework search path, this scaled quadratically with the number of modules being imported. E.g. a setup with 100 modules being imported form 100 module search paths could cause on the order of 10,000 checks of `FileSystem::exists`. While these checks are fairly fast (~10µs), they add up to ~100ms.
To improve this, perform a first scan of all module search paths and list the files they contain. From this, create a lookup map that maps filenames to the search paths they can be found in. E.g. for
```
searchPath1/
Module1.framework
searchPath2/
Module1.framework
Module2.swiftmodule
```
we create the following lookup table
```
Module1.framework -> [searchPath1, searchPath2]
Module2.swiftmodule -> [searchPath2]
```
