rust: Add support to emit certain Cargo env vars.

Some crates expect Cargo to provide certain environment variables. This
CL adds a compatability flag that emulates the behavior of Cargo by
setting these environment variables when building.

Bug: 171011485
Test: New soong tests pass
Test: quiche no longer requires patch removing CARGO_PKG_VERSION
Change-Id: I4c95c284846f6075428c6f61fe8c260f2e35fbd9

rust/builder.go

@@ -269,6 +269,17 @@ func transformSrctoCrate(ctx ModuleContext, main android.Path, deps PathDeps, fl
 
 	envVars = append(envVars, "ANDROID_RUST_VERSION="+config.RustDefaultVersion)
 
+	if ctx.RustModule().compiler.CargoEnvCompat() {
+		if _, ok := ctx.RustModule().compiler.(*binaryDecorator); ok {
+			envVars = append(envVars, "CARGO_BIN_NAME="+strings.TrimSuffix(outputFile.Base(), outputFile.Ext()))
+		}
+		envVars = append(envVars, "CARGO_CRATE_NAME="+ctx.RustModule().CrateName())
+		pkgVersion := ctx.RustModule().compiler.CargoPkgVersion()
+		if pkgVersion != "" {
+			envVars = append(envVars, "CARGO_PKG_VERSION="+pkgVersion)
+		}
+	}
+
 	if flags.Clippy {
 		clippyFile := android.PathForModuleOut(ctx, outputFile.Base()+".clippy")
 		ctx.Build(pctx, android.BuildParams{