feat: implement bob_toolchain defaults

This commit enables `bob_toolchain` to be
applied by default for targets which do not
specify their toolchain explicitly.

Change-Id: I994200a6b688c1be81bcfee2fc951e4f4f7d2ded

Blueprints

@@ -28,6 +28,7 @@ bootstrap_go_package {
         "bob-flag",
         "bob-backend",
         "bob-tag",
+        "bob-toolchain-mapper",
     ],
     srcs: [
         "core/alias.go",

core/BUILD.bazel

@@ -73,6 +73,7 @@ go_library(
         "//core/module",
         "//core/tag",
         "//core/toolchain",
+        "//core/toolchain/mapper",
         "//internal/bpwriter",
         "//internal/ccflags",
         "//internal/escape",

core/build_structs.go

@@ -350,24 +350,30 @@ func dependerMutator(ctx blueprint.BottomUpMutatorContext) {
 		ctx.AddVariationDependencies(nil, tag.SharedTag, build.Shared_libs...)
 	}
 
+	toolchainDefault := ToolchainModuleMap.Get(ctx.ModuleDir())
+
+	// TODO: refactor this given the duplicated code pattern here.
 	if sl, ok := ctx.Module().(*ModuleStrictLibrary); ok {
 		ctx.AddVariationDependencies(nil, tag.DepTag, sl.Properties.Deps...)
-		if sl.Properties.Toolchain != nil {
-			ctx.AddVariationDependencies(nil, tag.ToolchainTag, *sl.Properties.Toolchain)
+		toolchain := proptools.StringDefault(sl.Properties.Toolchain, toolchainDefault)
+		if toolchain != "" {
+			ctx.AddVariationDependencies(nil, tag.ToolchainTag, toolchain)
 		}
 	}
 
 	if sb, ok := ctx.Module().(*ModuleStrictBinary); ok {
 		ctx.AddVariationDependencies(nil, tag.DepTag, sb.Properties.Deps...)
-		if sb.Properties.Toolchain != nil {
-			ctx.AddVariationDependencies(nil, tag.ToolchainTag, *sb.Properties.Toolchain)
+		toolchain := proptools.StringDefault(sb.Properties.Toolchain, toolchainDefault)
+		if toolchain != "" {
+			ctx.AddVariationDependencies(nil, tag.ToolchainTag, toolchain)
 		}
 	}
 
 	if t, ok := ctx.Module().(*ModuleTest); ok {
 		ctx.AddVariationDependencies(nil, tag.DepTag, t.Properties.Deps...)
-		if t.Properties.Toolchain != nil {
-			ctx.AddVariationDependencies(nil, tag.ToolchainTag, *t.Properties.Toolchain)
+		toolchain := proptools.StringDefault(t.Properties.Toolchain, toolchainDefault)
+		if toolchain != "" {
+			ctx.AddVariationDependencies(nil, tag.ToolchainTag, toolchain)
 		}
 	}
 

core/module_toolchain.go

@@ -6,6 +6,7 @@ import (
 	"github.com/ARM-software/bob-build/core/flag"
 	"github.com/ARM-software/bob-build/core/module"
 	"github.com/ARM-software/bob-build/core/toolchain"
+	"github.com/ARM-software/bob-build/core/toolchain/mapper"
 	"github.com/google/blueprint"
 )
 
@@ -201,3 +202,11 @@ func ModuleToolchainFactory(config *BobConfig) (blueprint.Module, []interface{})
 	return module, []interface{}{&module.Properties,
 		&module.SimpleName.Properties}
 }
+
+var ToolchainModuleMap = mapper.New() // Global lookup for toolchain names
+
+func RegisterToolchainModules(ctx blueprint.EarlyMutatorContext) {
+	if _, ok := ctx.Module().(*ModuleToolchain); ok {
+		ToolchainModuleMap.Add(ctx.ModuleDir(), ctx.ModuleName())
+	}
+}

core/standalone.go

@@ -151,6 +151,7 @@ func Main() {
 	// The depender mutator adds the dependencies between binaries and libraries.
 	//
 	// The generated depender mutator add dependencies to generated source modules.
+	ctx.RegisterEarlyMutator("register_toolchains", RegisterToolchainModules)
 	ctx.RegisterBottomUpMutator("default_deps1", DefaultDepsStage1Mutator).Parallel()
 	ctx.RegisterBottomUpMutator("default_deps2", DefaultDepsStage2Mutator).Parallel()
 	ctx.RegisterTopDownMutator("features_applier", featureApplierMutator).Parallel()

docs/module_types/bob_toolchain.md

@@ -47,3 +47,34 @@ bob_library {
 }
 
 ```
+
+## Default Behaviour
+
+A `bob_toolchain` will be applied to the current directory scope and recursively into child directories, unless
+overwritten by another `bob_toolchain`.
+
+This toolchain is only applied to modules which support it.
+
+Take the following project structure as an example:
+
+```
+.
+├── build.bp >>> `bob_toolchain("A")`
+├── inherits
+│   ├── build.bp
+│   └── overwrite
+│       ├── build.bp >>> `bob_toolchain("B")`
+│       └── parent
+│           └── build.bp
+```
+
+In this case the mapping will be:
+
+```
+`.` -> `A`
+`./inherits` -> `A`
+`./inherits/overwrite` -> `B`
+`./inherits/overwrite/parent` -> `B`
+```
+
+> `bob_toolchain` module attributes are overwritten, and **_not_** merged.

gendiffer/tests/toolchain/nesting/app/bplist

@@ -0,0 +1,4 @@
+inherits/overwrite/parent/build.bp
+inherits/overwrite/build.bp
+inherits/build.bp
+build.bp

gendiffer/tests/toolchain/nesting/app/build.bp

@@ -0,0 +1,14 @@
+bob_toolchain {
+    name: "default_toolchain_config",
+    cflags: [
+        "-DROOT_TOOLCHAIN=1",
+    ],
+}
+
+bob_library {
+    name: "foo",
+    srcs: [
+        "src.c",
+    ],
+    build_by_default: true,
+}

gendiffer/tests/toolchain/nesting/app/inherits/build.bp

@@ -0,0 +1,8 @@
+bob_library {
+    name: "uses_root",
+    srcs: [
+        "src.c",
+    ],
+    build_by_default: true,
+
+}

gendiffer/tests/toolchain/nesting/app/inherits/overwrite/build.bp

@@ -0,0 +1,15 @@
+bob_toolchain {
+    name: "overwrites_toolchain_config",
+    cflags: [
+        "-DOVERWRITES_TOOLCHAIN=1",
+    ],
+}
+
+bob_library {
+    name: "overwrites",
+    srcs: [
+        "src.c",
+    ],
+    build_by_default: true,
+
+}

gendiffer/tests/toolchain/nesting/app/inherits/overwrite/parent/build.bp

@@ -0,0 +1,10 @@
+
+
+bob_library {
+    name: "parent",
+    srcs: [
+        "src.c",
+    ],
+    build_by_default: true,
+
+}

gendiffer/tests/toolchain/nesting/out/android/Android.bp.out

@@ -0,0 +1,50 @@
+
+genrule {
+    name: "_check_buildbp_updates_redacted",
+    srcs: [
+        "build.bp",
+        "inherits/build.bp",
+        "inherits/overwrite/build.bp",
+        "inherits/overwrite/parent/build.bp",
+    ],
+    out: ["androidbp_up_to_date"],
+    tool_files: ["scripts/verify_hash.py"],
+    cmd: "python $(location scripts/verify_hash.py) --hash redacted --out $(out) -- $(in)",
+}
+
+cc_library {
+    name: "foo",
+    host_supported: false,
+    device_supported: true,
+    srcs: ["src.c"],
+    cflags: ["-DROOT_TOOLCHAIN=1"],
+    compile_multilib: "both",
+}
+
+cc_library {
+    name: "overwrites",
+    host_supported: false,
+    device_supported: true,
+    srcs: ["inherits/overwrite/src.c"],
+    cflags: ["-DOVERWRITES_TOOLCHAIN=1"],
+    compile_multilib: "both",
+}
+
+cc_library {
+    name: "parent",
+    host_supported: false,
+    device_supported: true,
+    srcs: ["inherits/overwrite/parent/src.c"],
+    cflags: ["-DOVERWRITES_TOOLCHAIN=1"],
+    compile_multilib: "both",
+}
+
+cc_library {
+    name: "uses_root",
+    host_supported: false,
+    device_supported: true,
+    srcs: ["inherits/src.c"],
+    cflags: ["-DROOT_TOOLCHAIN=1"],
+    compile_multilib: "both",
+}
+

gendiffer/tests/toolchain/nesting/out/android/expectedExitCode.int

@@ -0,0 +1 @@
+0