rust: made-to-order rust staticlibs

Whenever any two Rust static libraries are included
as static libraries anywhere in a CC dependency tree, we sometimes
get duplicate symbol errors. To avoid this, we no longer
directly link multiple rust static libs to CC modules.

Instead, we build rust_ffi_rlib modules and produce the actual
static library that gets linked against the CC module based on
that CC module's full list of Rust rlib dependencies.

This introduces a new static_rlibs property for cc modules to
define the rust_ffi_rlib dependencies, which are then used to
generate the module above.

This CL is intended to deprecate rust_ffi_static. It leaves
rust_ffi_static and rust_ffi static variants in place until
the remaining rust_ffi_static declarations and uses can be
removed. In the meantime, rust_ffi_static produces
rust_ffi_rlib variants as well to make the transition easier.

Bug: 254469782
Test: m # with no changes
Test: m libapexsupport # with static_rlibs
Test: m libunwindstack # with static_rlibs
Test: m netsimd # with static_rlibs, no duplicate symbols
Test: m blueprint_tests # New Soong tests

Change-Id: I47e27ac967ef0cad46d398ebf59d8275929ae28a

cc/builder.go

@@ -19,6 +19,7 @@ package cc
 // functions.
 
 import (
+	"fmt"
 	"path/filepath"
 	"runtime"
 	"strconv"
@@ -330,6 +331,15 @@ var (
 			CommandDeps: []string{"$cxxExtractor", "$kytheVnames"},
 		},
 		"cFlags")
+
+	// Function pointer for producting staticlibs from rlibs. Corresponds to
+	// rust.TransformRlibstoStaticlib(), initialized in soong-rust (rust/builder.go init())
+	//
+	// This is required since soong-rust depends on soong-cc, so soong-cc cannot depend on soong-rust
+	// without resulting in a circular dependency. Setting this function pointer in soong-rust allows
+	// soong-cc to call into this particular function.
+	TransformRlibstoStaticlib (func(ctx android.ModuleContext, mainSrc android.Path, deps []RustRlibDep,
+		outputFile android.WritablePath) android.Path) = nil
 )
 
 func PwdPrefix() string {
@@ -774,6 +784,47 @@ func transformObjToStaticLib(ctx android.ModuleContext,
 	}
 }
 
+// Generate a Rust staticlib from a list of rlibDeps. Returns nil if TransformRlibstoStaticlib is nil or rlibDeps is empty.
+func generateRustStaticlib(ctx android.ModuleContext, rlibDeps []RustRlibDep) android.Path {
+	if TransformRlibstoStaticlib == nil && len(rlibDeps) > 0 {
+		// This should only be reachable if a module defines static_rlibs and
+		// soong-rust hasn't been loaded alongside soong-cc (e.g. in soong-cc tests).
+		panic(fmt.Errorf("TransformRlibstoStaticlib is not set and static_rlibs is defined in %s", ctx.ModuleName()))
+	} else if len(rlibDeps) == 0 {
+		return nil
+	}
+
+	output := android.PathForModuleOut(ctx, "generated_rust_staticlib", "lib"+ctx.ModuleName()+"_rust_staticlib.a")
+	stemFile := output.ReplaceExtension(ctx, "rs")
+	crateNames := []string{}
+
+	// Collect crate names
+	for _, lib := range rlibDeps {
+		// Exclude libstd so this can support no_std builds.
+		if lib.CrateName != "libstd" {
+			crateNames = append(crateNames, lib.CrateName)
+		}
+	}
+
+	// Deduplicate any crateNames just to be safe
+	crateNames = android.FirstUniqueStrings(crateNames)
+
+	// Write the source file
+	android.WriteFileRule(ctx, stemFile, genRustStaticlibSrcFile(crateNames))
+
+	return TransformRlibstoStaticlib(ctx, stemFile, rlibDeps, output)
+}
+
+func genRustStaticlibSrcFile(crateNames []string) string {
+	lines := []string{
+		"// @Soong generated Source",
+	}
+	for _, crate := range crateNames {
+		lines = append(lines, fmt.Sprintf("extern crate %s;", crate))
+	}
+	return strings.Join(lines, "\n")
+}
+
 // Generate a rule for compiling multiple .o files, plus static libraries, whole static libraries,
 // and shared libraries, to a shared library (.so) or dynamic executable
 func transformObjToDynamicBinary(ctx android.ModuleContext,