rust: Allow modules to use only generated sources

Removes the need for rust_test modules that test generated source to
define a source file that simply calls include()! to pull in the
generated source.

Bug: 196076408
Test: m libselinux_bindgen_test
Change-Id: I600301ab74f6ece861916fa2545b061c81b0d92d

1 files changed, 12 insertions, 2 deletions

diff --git a/rust/compiler.go b/rust/compiler.go
index de59f39ac..04fef3580 100644
--- a/rust/compiler.go
+++ b/rust/compiler.go
@@ -65,7 +65,11 @@ const (
 )
 
 type BaseCompilerProperties struct {
-	// path to the source file that is the main entry point of the program (e.g. main.rs or lib.rs)
+	// 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"`
 
 	// name of the lint set that should be used to validate this module.
@@ -420,12 +424,18 @@ func srcPathFromModuleSrcs(ctx ModuleContext, srcs []string) (android.Path, andr
 			srcIndex = i
 		}
 	}
-	if numSrcs != 1 {
+	if numSrcs > 1 {
 		ctx.PropertyErrorf("srcs", 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 {
 		ctx.PropertyErrorf("srcs", "main source file must be the first in srcs")
+	} else if numSrcs > 1 {
+		ctx.PropertyErrorf("srcs", "only a single generated source module can be defined without a main source file.")
 	}
+
 	paths := android.PathsForModuleSrc(ctx, srcs)
 	return paths[srcIndex], paths[1:]
 }