rust/compiler.go

// Copyright 2019 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package rust

import (
	"android/soong/cc"
	"errors"
	"fmt"
	"path/filepath"
	"strings"

	"github.com/google/blueprint/proptools"

	"android/soong/android"
	"android/soong/rust/config"
)

type RustLinkage int

const (
	DylibLinkage RustLinkage = iota
	RlibLinkage
)

type compiler interface {
	initialize(ctx ModuleContext)
	compilerFlags(ctx ModuleContext, flags Flags) Flags
	cfgFlags(ctx ModuleContext, flags Flags) Flags
	featureFlags(ctx ModuleContext, module *Module, flags Flags) Flags
	baseCompilerProps() BaseCompilerProperties
	compilerProps() []interface{}
	compile(ctx ModuleContext, flags Flags, deps PathDeps) buildOutput
	compilerDeps(ctx DepsContext, deps Deps) Deps
	crateName() string
	edition() string
	features(ctx android.ConfigurableEvaluatorContext, module *Module) []string
	rustdoc(ctx ModuleContext, flags Flags, deps PathDeps) android.OptionalPath
	Thinlto() bool

	// Output directory in which source-generated code from dependencies is
	// copied. This is equivalent to Cargo's OUT_DIR variable.
	cargoOutDir() android.OptionalPath

	// cargoPkgVersion returns the value of the Cargo_pkg_version property.
	cargoPkgVersion() string

	// cargoEnvCompat returns whether Cargo environment variables should be used.
	cargoEnvCompat() bool

	inData() bool
	install(ctx ModuleContext)
	relativeInstallPath() string
	everInstallable() bool

	nativeCoverage() bool

	Disabled() bool
	SetDisabled()

	stdLinkage(device bool) RustLinkage
	noStdlibs() bool

	unstrippedOutputFilePath() android.Path
	strippedOutputFilePath() android.OptionalPath

	checkedCrateRootPath() (android.Path, error)

	Aliases() map[string]string
}

func (compiler *baseCompiler) edition() string {
	return proptools.StringDefault(compiler.Properties.Edition, config.DefaultEdition)
}

func (compiler *baseCompiler) setNoStdlibs() {
	compiler.Properties.No_stdlibs = proptools.BoolPtr(true)
}

func (compiler *baseCompiler) disableLints() {
	compiler.Properties.Lints = proptools.StringPtr("none")
}

func NewBaseCompiler(dir, dir64 string, location installLocation) *baseCompiler {
	return &baseCompiler{
		Properties: BaseCompilerProperties{},
		dir:        dir,
		dir64:      dir64,
		location:   location,
	}
}

type installLocation int

const (
	InstallInSystem installLocation = 0
	InstallInData                   = iota

	incorrectSourcesError = "srcs can only contain one path for a rust file and source providers prefixed by \":\""
	genSubDir             = "out/"
)

type BaseCompilerProperties struct {
	// path to the source file that is the main entry point of the program (e.g. main.rs or lib.rs).
	// Only a single source file can be defined. Modules which generate source can be included by prefixing
	// the module name with ":", for example ":libfoo_bindgen"
	//
	// If no source file is defined, a single generated source module can be defined to be used as the main source.
	Srcs []string `android:"path,arch_variant"`

	// Entry point that is passed to rustc to begin the compilation. E.g. main.rs or lib.rs.
	// When this property is set,
	//    * sandboxing is enabled for this module, and
	//    * the srcs attribute is interpreted as a list of all source files potentially
	//          used in compilation, including the entrypoint, and
	//    * compile_data can be used to add additional files used in compilation that
	//          not directly used as source files.
	Crate_root *string `android:"path,arch_variant"`

	// name of the lint set that should be used to validate this module.
	//
	// Possible values are "default" (for using a sensible set of lints
	// depending on the module's location), "android" (for the strictest
	// lint set that applies to all Android platform code), "vendor" (for
	// a relaxed set) and "none" (for ignoring all lint warnings and
	// errors). The default value is "default".
	Lints *string

	// flags to pass to rustc. To enable configuration options or features, use the "cfgs" or "features" properties.
	Flags []string `android:"arch_variant"`

	// flags to pass to the linker
	Ld_flags []string `android:"arch_variant"`

	// Rust crate dependencies to rename. Each entry should be a string of the form "dependencyname:alias".
	//
	// "dependencyname" here should be the name of the crate, not the Android module. This is
	// equivalent to writing `alias = { package = "dependencyname" }` in a `Cargo.toml`.
	Aliases []string

	// list of rust rlib crate dependencies
	Rlibs proptools.Configurable[[]string] `android:"arch_variant"`

	// list of rust automatic crate dependencies.
	// Rustlibs linkage is rlib for host targets and dylib for device targets.
	Rustlibs proptools.Configurable[[]string] `android:"arch_variant"`

	// list of rust proc_macro crate dependencies
	Proc_macros proptools.Configurable[[]string] `android:"arch_variant"`

	// list of C shared library dependencies
	Shared_libs proptools.Configurable[[]string] `android:"arch_variant"`

	// list of C static library dependencies. These dependencies do not normally propagate to dependents
	// and may need to be redeclared. See whole_static_libs for bundling static dependencies into a library.
	Static_libs proptools.Configurable[[]string] `android:"arch_variant"`

	// Similar to static_libs, but will bundle the static library dependency into a library. This is helpful
	// to avoid having to redeclare the dependency for dependents of this library, but in some cases may also
	// result in bloat if multiple dependencies all include the same static library whole.
	//
	// The common use case for this is when the static library is unlikely to be a dependency of other modules to avoid
	// having to redeclare the static library dependency for every dependent module.
	// If you are not sure what to, for rust_library modules most static dependencies should go in static_libraries,
	// and for rust_ffi modules most static dependencies should go into whole_static_libraries.
	//
	// For rust_ffi static variants, these libraries will be included in the resulting static library archive.
	//
	// For rust_library rlib variants, these libraries will be bundled into the resulting rlib library. This will
	// include all of the static libraries symbols in any dylibs or binaries which use this rlib as well.
	Whole_static_libs proptools.Configurable[[]string] `android:"arch_variant"`

	// list of Rust system library dependencies.
	//
	// This is usually only needed when `no_stdlibs` is true, in which case it can be used to depend on system crates
	// like `core` and `alloc`.
	Stdlibs proptools.Configurable[[]string] `android:"arch_variant"`

	// crate name, required for modules which produce Rust libraries: rust_library, rust_ffi and SourceProvider
	// modules which create library variants (rust_bindgen). This must be the expected extern crate name used in
	// source, and is required to conform to an enforced format matching library output files (if the output file is
	// lib<someName><suffix>, the crate_name property must be <someName>).
	Crate_name string `android:"arch_variant"`

	// list of features to enable for this crate
	Features proptools.Configurable[[]string] `android:"arch_variant"`

	// list of configuration options to enable for this crate. To enable features, use the "features" property.
	Cfgs proptools.Configurable[[]string] `android:"arch_variant"`

	// specific rust edition that should be used if the default version is not desired
	Edition *string `android:"arch_variant"`

	// sets name of the output
	Stem *string `android:"arch_variant"`

	// append to name of output
	Suffix *string `android:"arch_variant"`

	// install to a subdirectory of the default install path for the module
	Relative_install_path *string `android:"arch_variant"`

	// whether to suppress inclusion of standard crates - defaults to false
	No_stdlibs *bool `android:"arch_variant"`

	// Change the rustlibs linkage to select rlib linkage by default for device targets.
	// Also link libstd as an rlib as well on device targets.
	// Note: This is the default behavior for host targets.
	//
	// This is primarily meant for rust_binary and rust_ffi modules where the default
	// linkage of libstd might need to be overridden in some use cases. This should
	// generally be avoided with other module types since it may cause collisions at
	// linkage if all dependencies of the root binary module do not link against libstd
	// the same way.
	Prefer_rlib *bool `android:"arch_variant"`

	// Enables emitting certain Cargo environment variables. Only intended to be used for compatibility purposes.
	// Will set CARGO_CRATE_NAME to the crate_name property's value.
	// Will set CARGO_BIN_NAME to the output filename value without the extension.
	Cargo_env_compat *bool

	// If cargo_env_compat is true, sets the CARGO_PKG_VERSION env var to this value.
	Cargo_pkg_version *string

	// Control whether LTO is used for the final (Rust) linkage. This does not impact
	// cross-language LTO.
	Lto struct {
		// Whether thin LTO should be enabled. By default this is true.
		// LTO provides such a large code size benefit for Rust, this should always
		// be enabled for production builds unless there's a clear need to disable it.
		Thin *bool `android:"arch_variant"`
	} `android:"arch_variant"`
}

type baseCompiler struct {
	Properties BaseCompilerProperties

	// Install related
	dir      string
	dir64    string
	subDir   string
	relative string
	path     android.InstallPath
	location installLocation
	sanitize *sanitize

	distFile android.OptionalPath

	installDeps android.InstallPaths

	// unstripped output file.
	unstrippedOutputFile android.Path

	// stripped output file.
	strippedOutputFile android.OptionalPath

	// If a crate has a source-generated dependency, a copy of the source file
	// will be available in cargoOutDir (equivalent to Cargo OUT_DIR).
	// This is stored internally because it may not be available during
	// singleton-generation passes like rustdoc/rust_project.json, but should
	// be stashed during initial generation.
	cachedCargoOutDir android.ModuleOutPath
	// Calculated crate root cached internally because ModuleContext is not
	// available to singleton targets like rustdoc/rust_project.json
	cachedCrateRootPath android.Path
	// If cachedCrateRootPath is nil after initialization, this will contain
	// an explanation of why
	cachedCrateRootError error
}

func (compiler *baseCompiler) Disabled() bool {
	return false
}

// Thin LTO is enabled by default.
func (compiler *baseCompiler) Thinlto() bool {
	return BoolDefault(compiler.Properties.Lto.Thin, true)
}

func (compiler *baseCompiler) SetDisabled() {
	panic("baseCompiler does not implement SetDisabled()")
}

func (compiler *baseCompiler) noStdlibs() bool {
	return Bool(compiler.Properties.No_stdlibs)
}

func (compiler *baseCompiler) coverageOutputZipPath() android.OptionalPath {
	panic("baseCompiler does not implement coverageOutputZipPath()")
}

func (compiler *baseCompiler) preferRlib() bool {
	return Bool(compiler.Properties.Prefer_rlib)
}

func (compiler *baseCompiler) Aliases() map[string]string {
	aliases := map[string]string{}
	for _, entry := range compiler.Properties.Aliases {
		dep, alias, found := strings.Cut(entry, ":")
		if !found {
			panic(fmt.Errorf("invalid aliases entry %q missing ':'", entry))
		}
		aliases[dep] = alias
	}
	return aliases
}

func (compiler *baseCompiler) stdLinkage(device bool) RustLinkage {
	// For devices, we always link stdlibs in as dylibs by default.
	if compiler.preferRlib() {
		return RlibLinkage
	} else if device {
		return DylibLinkage
	} else {
		return RlibLinkage
	}
}

var _ compiler = (*baseCompiler)(nil)

func (compiler *baseCompiler) inData() bool {
	return compiler.location == InstallInData
}

func (compiler *baseCompiler) compilerProps() []interface{} {
	return []interface{}{&compiler.Properties}
}

func (compiler *baseCompiler) baseCompilerProps() BaseCompilerProperties {
	return compiler.Properties
}

func cfgsToFlags(cfgs []string) []string {
	flags := make([]string, 0, len(cfgs))
	for _, cfg := range cfgs {
		flags = append(flags, "--cfg '"+cfg+"'")
	}

	return flags
}

func (compiler *baseCompiler) features(ctx android.ConfigurableEvaluatorContext, module *Module) []string {
	eval := module.ConfigurableEvaluator(ctx)
	return compiler.Properties.Features.GetOrDefault(eval, nil)
}

func (compiler *baseCompiler) featuresToFlags(ctx android.ConfigurableEvaluatorContext, module *Module) []string {
	flags := []string{}
	for _, feature := range compiler.features(ctx, module) {
		flags = append(flags, "--cfg 'feature=\""+feature+"\"'")
	}

	return flags
}

func (compiler *baseCompiler) featureFlags(ctx ModuleContext, module *Module, flags Flags) Flags {
	flags.RustFlags = append(flags.RustFlags, compiler.featuresToFlags(ctx, module)...)
	flags.RustdocFlags = append(flags.RustdocFlags, compiler.featuresToFlags(ctx, module)...)

	return flags
}

func CommonDefaultCfgFlags(flags Flags, vendor bool, product bool) Flags {
	var cfgs []string
	if vendor || product {
		cfgs = append(cfgs, "android_vndk")
		if vendor {
			cfgs = append(cfgs, "android_vendor")
		} else if product {
			cfgs = append(cfgs, "android_product")
		}
	}

	flags.RustFlags = append(flags.RustFlags, cfgsToFlags(cfgs)...)
	flags.RustdocFlags = append(flags.RustdocFlags, cfgsToFlags(cfgs)...)
	return flags
}

func (compiler *baseCompiler) cfgFlags(ctx ModuleContext, flags Flags) Flags {
	flags = CommonDefaultCfgFlags(flags, ctx.RustModule().InVendor(), ctx.RustModule().InProduct())

	cfgFlags := cfgsToFlags(compiler.Properties.Cfgs.GetOrDefault(ctx, nil))
	flags.RustFlags = append(flags.RustFlags, cfgFlags...)
	flags.RustdocFlags = append(flags.RustdocFlags, cfgFlags...)

	return flags
}

func CommonDefaultFlags(ctx android.ModuleContext, toolchain config.Toolchain, flags Flags) Flags {
	flags.GlobalRustFlags = append(flags.GlobalRustFlags, config.GlobalRustFlags...)
	flags.GlobalRustFlags = append(flags.GlobalRustFlags, toolchain.ToolchainRustFlags())
	flags.GlobalLinkFlags = append(flags.GlobalLinkFlags, toolchain.ToolchainLinkFlags())
	flags.EmitXrefs = ctx.Config().EmitXrefRules()

	if ctx.Host() && !ctx.Windows() {
		flags.LinkFlags = append(flags.LinkFlags, cc.RpathFlags(ctx)...)
	}

	if ctx.Os() == android.Linux {
		// Add -lc, -lrt, -ldl, -lpthread, -lm and -lgcc_s to glibc builds to match
		// the default behavior of device builds.
		flags.LinkFlags = append(flags.LinkFlags, config.LinuxHostGlobalLinkFlags...)
	} else if ctx.Os() == android.Darwin {
		// Add -lc, -ldl, -lpthread and -lm to glibc darwin builds to match the default
		// behavior of device builds.
		flags.LinkFlags = append(flags.LinkFlags,
			"-lc",
			"-ldl",
			"-lpthread",
			"-lm",
		)
	}
	return flags
}

func (compiler *baseCompiler) compilerFlags(ctx ModuleContext, flags Flags) Flags {

	flags = CommonDefaultFlags(ctx, ctx.toolchain(), flags)
	lintFlags, err := config.RustcLintsForDir(ctx.ModuleDir(), compiler.Properties.Lints)
	if err != nil {
		ctx.PropertyErrorf("lints", err.Error())
	}

	// linkage-related flags are disallowed.
	for _, s := range compiler.Properties.Ld_flags {
		if strings.HasPrefix(s, "-Wl,-l") || strings.HasPrefix(s, "-Wl,-L") {
			ctx.PropertyErrorf("ld_flags", "'-Wl,-l' and '-Wl,-L' flags cannot be manually specified")
		}
	}
	for _, s := range compiler.Properties.Flags {
		if strings.HasPrefix(s, "-l") || strings.HasPrefix(s, "-L") {
			ctx.PropertyErrorf("flags", "'-l' and '-L' flags cannot be manually specified")
		}
		if strings.HasPrefix(s, "--extern") {
			ctx.PropertyErrorf("flags", "'--extern' flag cannot be manually specified")
		}
		if strings.HasPrefix(s, "-Clink-args=") || strings.HasPrefix(s, "-C link-args=") {
			ctx.PropertyErrorf("flags", "'-C link-args' flag cannot be manually specified")
		}
	}

	flags.RustFlags = append(flags.RustFlags, lintFlags)
	flags.RustFlags = append(flags.RustFlags, compiler.Properties.Flags...)
	flags.RustFlags = append(flags.RustFlags, "--edition="+compiler.edition())
	flags.RustdocFlags = append(flags.RustdocFlags, "--edition="+compiler.edition())
	flags.LinkFlags = append(flags.LinkFlags, compiler.Properties.Ld_flags...)

	return flags
}

func (compiler *baseCompiler) compile(ctx ModuleContext, flags Flags, deps PathDeps) buildOutput {
	panic(fmt.Errorf("baseCrater doesn't know how to crate things!"))
}

func (compiler *baseCompiler) rustdoc(ctx ModuleContext, flags Flags,
	deps PathDeps) android.OptionalPath {

	return android.OptionalPath{}
}

func (compiler *baseCompiler) initialize(ctx ModuleContext) {
	compiler.cachedCargoOutDir = android.PathForModuleOut(ctx, genSubDir)
	if compiler.Properties.Crate_root == nil {
		compiler.cachedCrateRootPath, compiler.cachedCrateRootError = srcPathFromModuleSrcs(ctx, compiler.Properties.Srcs)
	} else {
		compiler.cachedCrateRootPath = android.PathForModuleSrc(ctx, *compiler.Properties.Crate_root)
		compiler.cachedCrateRootError = nil
	}
}

func (compiler *baseCompiler) cargoOutDir() android.OptionalPath {
	return android.OptionalPathForPath(compiler.cachedCargoOutDir)
}

func (compiler *baseCompiler) cargoEnvCompat() bool {
	return Bool(compiler.Properties.Cargo_env_compat)
}

func (compiler *baseCompiler) cargoPkgVersion() string {
	return String(compiler.Properties.Cargo_pkg_version)
}

func (compiler *baseCompiler) unstrippedOutputFilePath() android.Path {
	return compiler.unstrippedOutputFile
}

func (compiler *baseCompiler) strippedOutputFilePath() android.OptionalPath {
	return compiler.strippedOutputFile
}

func (compiler *baseCompiler) compilerDeps(ctx DepsContext, deps Deps) Deps {
	deps.Rlibs = append(deps.Rlibs, compiler.Properties.Rlibs.GetOrDefault(ctx, nil)...)
	deps.Rustlibs = append(deps.Rustlibs, compiler.Properties.Rustlibs.GetOrDefault(ctx, nil)...)
	deps.ProcMacros = append(deps.ProcMacros, compiler.Properties.Proc_macros.GetOrDefault(ctx, nil)...)
	deps.StaticLibs = append(deps.StaticLibs, compiler.Properties.Static_libs.GetOrDefault(ctx, nil)...)
	deps.WholeStaticLibs = append(deps.WholeStaticLibs, compiler.Properties.Whole_static_libs.GetOrDefault(ctx, nil)...)
	deps.SharedLibs = append(deps.SharedLibs, compiler.Properties.Shared_libs.GetOrDefault(ctx, nil)...)
	deps.Stdlibs = append(deps.Stdlibs, compiler.Properties.Stdlibs.GetOrDefault(ctx, nil)...)

	if !Bool(compiler.Properties.No_stdlibs) {
		for _, stdlib := range config.Stdlibs {
			// If we're building for the build host, use the prebuilt stdlibs, unless the host
			// is linux_bionic which doesn't have prebuilts.
			if ctx.Host() && !ctx.Target().HostCross && ctx.Target().Os != android.LinuxBionic {
				stdlib = "prebuilt_" + stdlib
			}
			deps.Stdlibs = append(deps.Stdlibs, stdlib)
		}
	}
	return deps
}

func bionicDeps(ctx DepsContext, deps Deps, static bool) Deps {
	bionicLibs := []string{}
	bionicLibs = append(bionicLibs, "liblog")
	bionicLibs = append(bionicLibs, "libc")
	bionicLibs = append(bionicLibs, "libm")
	bionicLibs = append(bionicLibs, "libdl")

	if static {
		deps.StaticLibs = append(deps.StaticLibs, bionicLibs...)
	} else {
		deps.SharedLibs = append(deps.SharedLibs, bionicLibs...)
	}
	if ctx.RustModule().StaticExecutable() {
		deps.StaticLibs = append(deps.StaticLibs, "libunwind")
	}
	if libRuntimeBuiltins := config.BuiltinsRuntimeLibrary(ctx.toolchain()); libRuntimeBuiltins != "" {
		deps.StaticLibs = append(deps.StaticLibs, libRuntimeBuiltins)
	}
	return deps
}

func muslDeps(ctx DepsContext, deps Deps, static bool) Deps {
	muslLibs := []string{"libc_musl"}
	if static {
		deps.StaticLibs = append(deps.StaticLibs, muslLibs...)
	} else {
		deps.SharedLibs = append(deps.SharedLibs, muslLibs...)
	}
	if libRuntimeBuiltins := config.BuiltinsRuntimeLibrary(ctx.toolchain()); libRuntimeBuiltins != "" {
		deps.StaticLibs = append(deps.StaticLibs, libRuntimeBuiltins)
	}

	return deps
}

func (compiler *baseCompiler) crateName() string {
	return compiler.Properties.Crate_name
}

func (compiler *baseCompiler) everInstallable() bool {
	// Most modules are installable, so return true by default.
	return true
}

func (compiler *baseCompiler) installDir(ctx ModuleContext) android.InstallPath {
	dir := compiler.dir
	if ctx.toolchain().Is64Bit() && compiler.dir64 != "" {
		dir = compiler.dir64
	}
	if ctx.Target().NativeBridge == android.NativeBridgeEnabled {
		dir = filepath.Join(dir, ctx.Target().NativeBridgeRelativePath)
	}
	if !ctx.Host() && ctx.Config().HasMultilibConflict(ctx.Arch().ArchType) {
		dir = filepath.Join(dir, ctx.Arch().ArchType.String())
	}

	if compiler.location == InstallInData && ctx.RustModule().InVendorOrProduct() {
		if ctx.RustModule().InProduct() {
			dir = filepath.Join(dir, "product")
		} else if ctx.RustModule().InVendor() {
			dir = filepath.Join(dir, "vendor")
		} else {
			ctx.ModuleErrorf("Unknown data+VNDK installation kind")
		}
	}

	return android.PathForModuleInstall(ctx, dir, compiler.subDir,
		compiler.relativeInstallPath(), compiler.relative)
}

func (compiler *baseCompiler) nativeCoverage() bool {
	return false
}

func (compiler *baseCompiler) install(ctx ModuleContext) {
	path := ctx.RustModule().OutputFile()
	compiler.path = ctx.InstallFile(compiler.installDir(ctx), path.Path().Base(), path.Path(), compiler.installDeps...)
}

func (compiler *baseCompiler) installTestData(ctx ModuleContext, data []android.DataPath) {
	installedData := ctx.InstallTestData(compiler.installDir(ctx), data)
	compiler.installDeps = append(compiler.installDeps, installedData...)
}

func (compiler *baseCompiler) getStem(ctx android.ModuleContext) string {
	return compiler.getStemWithoutSuffix(ctx) + String(compiler.Properties.Suffix)
}

func (compiler *baseCompiler) getStemWithoutSuffix(ctx android.BaseModuleContext) string {
	stem := ctx.ModuleName()
	if String(compiler.Properties.Stem) != "" {
		stem = String(compiler.Properties.Stem)
	}

	return stem
}

func (compiler *baseCompiler) relativeInstallPath() string {
	return String(compiler.Properties.Relative_install_path)
}

func (compiler *baseCompiler) checkedCrateRootPath() (android.Path, error) {
	return compiler.cachedCrateRootPath, compiler.cachedCrateRootError
}

func crateRootPath(ctx ModuleContext, compiler compiler) android.Path {
	root, err := compiler.checkedCrateRootPath()
	if err != nil {
		ctx.PropertyErrorf("srcs", err.Error())
	}
	return root
}

// Returns the Path for the main source file along with Paths for generated source files from modules listed in srcs.
func srcPathFromModuleSrcs(ctx ModuleContext, srcs []string) (android.Path, error) {
	// The srcs can contain strings with prefix ":".
	// They are dependent modules of this module, with android.SourceDepTag.
	// They are not the main source file compiled by rustc.
	numSrcs := 0
	srcIndex := 0
	for i, s := range srcs {
		if android.SrcIsModule(s) == "" {
			numSrcs++
			srcIndex = i
		}
	}
	if numSrcs > 1 {
		return nil, errors.New(incorrectSourcesError)
	}

	// If a main source file is not provided we expect only a single SourceProvider module to be defined
	// within srcs, with the expectation that the first source it provides is the entry point.
	if srcIndex != 0 {
		return nil, errors.New("main source file must be the first in srcs")
	} else if numSrcs > 1 {
		return nil, errors.New("only a single generated source module can be defined without a main source file.")
	}

	// TODO: b/297264540 - once all modules are sandboxed, we need to select the proper
	// entry point file from Srcs rather than taking the first one
	paths := android.PathsForModuleSrc(ctx, srcs)
	if len(paths) == 0 {
		return nil, errors.New("srcs must not be empty")
	}
	return paths[srcIndex], nil
}