Prettify soong ninja build descriptions

Descriptions currently look like:
[  0% 4/29328] cc out-soong/.intermediates/external/clang/lib/Sema/libclangSema/android_arm_armv7-a-neon_denver_static_core/obj/external/clang/lib/Sema/SemaCodeComplete.o

This is not very helpful - most of the characters are used to show the
output path, which contains useful information like target architecture,
but also contains most of the path to the source files twice, and less
useful information like the exact variant name used by soong.
Make the descriptions look like:
[  0% 3/29329] //external/clang/lib/Sema:libclangSema clang++ SemaTemplateInstantiate.cpp

This is //path/to/module:modulename tool relative/path/to/source/file

Test: builds, looks pretty
Change-Id: I3087aa7d4eb1860ef6239d77407b8b35445616d7

16 files changed, 249 insertions, 187 deletions

diff --git a/android/api_levels.go b/android/api_levels.go
index c77ced16..70b251b6 100644
--- a/android/api_levels.go
+++ b/android/api_levels.go
@@ -16,6 +16,7 @@ package android
 
 import (
 	"encoding/json"
+	"path/filepath"
 
 	"github.com/google/blueprint"
 )
@@ -39,8 +40,9 @@ func createApiLevelsJson(ctx blueprint.SingletonContext, file string,
 	}
 
 	ctx.Build(pctx, blueprint.BuildParams{
-		Rule:    WriteFile,
-		Outputs: []string{file},
+		Rule:        WriteFile,
+		Description: "generate " + filepath.Base(file),
+		Outputs:     []string{file},
 		Args: map[string]string{
 			"content": string(jsonStr[:]),
 		},
diff --git a/android/arch.go b/android/arch.go
index 39477ad7..51fc444e 100644
--- a/android/arch.go
+++ b/android/arch.go
@@ -224,6 +224,21 @@ const (
 	HostCross
 )
 
+func (class OsClass) String() string {
+	switch class {
+	case Generic:
+		return "generic"
+	case Device:
+		return "device"
+	case Host:
+		return "host"
+	case HostCross:
+		return "host cross"
+	default:
+		panic(fmt.Errorf("unknown class %d", class))
+	}
+}
+
 func (os OsType) String() string {
 	return os.Name
 }
diff --git a/android/module.go b/android/module.go
index 90d61e2a..8f8f34b3 100644
--- a/android/module.go
+++ b/android/module.go
@@ -36,6 +36,7 @@ type ModuleBuildParams struct {
 	Rule            blueprint.Rule
 	Deps            blueprint.Deps
 	Depfile         WritablePath
+	Description     string
 	Output          WritablePath
 	Outputs         WritablePaths
 	ImplicitOutput  WritablePath
@@ -480,6 +481,23 @@ func (a *ModuleBase) GenerateBuildActions(ctx blueprint.ModuleContext) {
 		missingDeps:            ctx.GetMissingDependencies(),
 	}
 
+	desc := "//" + ctx.ModuleDir() + ":" + ctx.ModuleName() + " "
+	var suffix []string
+	if androidCtx.Os().Class != Device && androidCtx.Os().Class != Generic {
+		suffix = append(suffix, androidCtx.Os().String())
+	}
+	if !androidCtx.PrimaryArch() {
+		suffix = append(suffix, androidCtx.Arch().ArchType.String())
+	}
+
+	ctx.Variable(pctx, "moduleDesc", desc)
+
+	s := ""
+	if len(suffix) > 0 {
+		s = " [" + strings.Join(suffix, " ") + "]"
+	}
+	ctx.Variable(pctx, "moduleDescSuffix", s)
+
 	if a.Enabled() {
 		a.module.GenerateAndroidBuildActions(androidCtx)
 		if ctx.Failed() {
@@ -516,11 +534,12 @@ type androidModuleContext struct {
 	module          Module
 }
 
-func (a *androidModuleContext) ninjaError(outputs []string, err error) {
+func (a *androidModuleContext) ninjaError(desc string, outputs []string, err error) {
 	a.ModuleContext.Build(pctx, blueprint.BuildParams{
-		Rule:     ErrorRule,
-		Outputs:  outputs,
-		Optional: true,
+		Rule:        ErrorRule,
+		Description: desc,
+		Outputs:     outputs,
+		Optional:    true,
 		Args: map[string]string{
 			"error": err.Error(),
 		},
@@ -530,8 +549,9 @@ func (a *androidModuleContext) ninjaError(outputs []string, err error) {
 
 func (a *androidModuleContext) Build(pctx blueprint.PackageContext, params blueprint.BuildParams) {
 	if a.missingDeps != nil {
-		a.ninjaError(params.Outputs, fmt.Errorf("module %s missing dependencies: %s\n",
-			a.ModuleName(), strings.Join(a.missingDeps, ", ")))
+		a.ninjaError(params.Description, params.Outputs,
+			fmt.Errorf("module %s missing dependencies: %s\n",
+				a.ModuleName(), strings.Join(a.missingDeps, ", ")))
 		return
 	}
 
@@ -552,6 +572,10 @@ func (a *androidModuleContext) ModuleBuild(pctx blueprint.PackageContext, params
 		Optional:        !params.Default,
 	}
 
+	if params.Description != "" {
+		bparams.Description = "${moduleDesc}" + params.Description + "${moduleDescSuffix}"
+	}
+
 	if params.Depfile != nil {
 		bparams.Depfile = params.Depfile.String()
 	}
@@ -569,8 +593,9 @@ func (a *androidModuleContext) ModuleBuild(pctx blueprint.PackageContext, params
 	}
 
 	if a.missingDeps != nil {
-		a.ninjaError(bparams.Outputs, fmt.Errorf("module %s missing dependencies: %s\n",
-			a.ModuleName(), strings.Join(a.missingDeps, ", ")))
+		a.ninjaError(bparams.Description, bparams.Outputs,
+			fmt.Errorf("module %s missing dependencies: %s\n",
+				a.ModuleName(), strings.Join(a.missingDeps, ", ")))
 		return
 	}
 
@@ -624,6 +649,9 @@ func (a *androidBaseContextImpl) Debug() bool {
 }
 
 func (a *androidBaseContextImpl) PrimaryArch() bool {
+	if len(a.config.Targets[a.target.Os.Class]) <= 1 {
+		return true
+	}
 	return a.target.Arch.ArchType == a.config.Targets[a.target.Os.Class][0].Arch.ArchType
 }
 
@@ -686,12 +714,13 @@ func (a *androidModuleContext) InstallFileName(installPath OutputPath, name stri
 		}
 
 		a.ModuleBuild(pctx, ModuleBuildParams{
-			Rule:      Cp,
-			Output:    fullInstallPath,
-			Input:     srcPath,
-			Implicits: implicitDeps,
-			OrderOnly: orderOnlyDeps,
-			Default:   !a.AConfig().EmbeddedInMake(),
+			Rule:        Cp,
+			Description: "install " + fullInstallPath.Base(),
+			Output:      fullInstallPath,
+			Input:       srcPath,
+			Implicits:   implicitDeps,
+			OrderOnly:   orderOnlyDeps,
+			Default:     !a.AConfig().EmbeddedInMake(),
 		})
 
 		a.installFiles = append(a.installFiles, fullInstallPath)
@@ -711,10 +740,11 @@ func (a *androidModuleContext) InstallSymlink(installPath OutputPath, name strin
 	if !a.skipInstall(fullInstallPath) {
 
 		a.ModuleBuild(pctx, ModuleBuildParams{
-			Rule:      Symlink,
-			Output:    fullInstallPath,
-			OrderOnly: Paths{srcPath},
-			Default:   !a.AConfig().EmbeddedInMake(),
+			Rule:        Symlink,
+			Description: "install symlink " + fullInstallPath.Base(),
+			Output:      fullInstallPath,
+			OrderOnly:   Paths{srcPath},
+			Default:     !a.AConfig().EmbeddedInMake(),
 			Args: map[string]string{
 				"fromPath": srcPath.String(),
 			},
diff --git a/cc/builder.go b/cc/builder.go
index 8a0c7f4c..a4fda5bc 100644
--- a/cc/builder.go
+++ b/cc/builder.go
@@ -45,7 +45,6 @@ var (
 			Deps:        blueprint.DepsGCC,
 			Command:     "$relPwd ${config.CcWrapper}$ccCmd -c $cFlags -MD -MF ${out}.d -o $out $in",
 			CommandDeps: []string{"$ccCmd"},
-			Description: "cc $out",
 		},
 		"ccCmd", "cFlags")
 
@@ -54,7 +53,6 @@ var (
 			Command: "$ldCmd ${crtBegin} @${out}.rsp " +
 				"${libFlags} ${crtEnd} -o ${out} ${ldFlags}",
 			CommandDeps:    []string{"$ldCmd"},
-			Description:    "ld $out",
 			Rspfile:        "${out}.rsp",
 			RspfileContent: "${in}",
 		},
@@ -64,7 +62,6 @@ var (
 		blueprint.RuleParams{
 			Command:     "$ldCmd -nostdlib -Wl,-r ${in} -o ${out} ${ldFlags}",
 			CommandDeps: []string{"$ldCmd"},
-			Description: "partialLd $out",
 		},
 		"ldCmd", "ldFlags")
 
@@ -72,7 +69,6 @@ var (
 		blueprint.RuleParams{
 			Command:        "rm -f ${out} && $arCmd $arFlags $out @${out}.rsp",
 			CommandDeps:    []string{"$arCmd"},
-			Description:    "ar $out",
 			Rspfile:        "${out}.rsp",
 			RspfileContent: "${in}",
 		},
@@ -82,7 +78,6 @@ var (
 		blueprint.RuleParams{
 			Command:     "rm -f ${out} && ${config.MacArPath} $arFlags $out $in",
 			CommandDeps: []string{"${config.MacArPath}"},
-			Description: "ar $out",
 		},
 		"arFlags")
 
@@ -90,7 +85,6 @@ var (
 		blueprint.RuleParams{
 			Command:     "cp -f ${inAr} ${out}.tmp && ${config.MacArPath} $arFlags ${out}.tmp $in && mv ${out}.tmp ${out}",
 			CommandDeps: []string{"${config.MacArPath}", "${inAr}"},
-			Description: "ar $out",
 		},
 		"arFlags", "inAr")
 
@@ -98,14 +92,12 @@ var (
 		blueprint.RuleParams{
 			Command:     "${config.MacStripPath} -u -r -o $out $in",
 			CommandDeps: []string{"${config.MacStripPath}"},
-			Description: "strip $out",
 		})
 
 	prefixSymbols = pctx.AndroidStaticRule("prefixSymbols",
 		blueprint.RuleParams{
 			Command:     "$objcopyCmd --prefix-symbols=${prefix} ${in} ${out}",
 			CommandDeps: []string{"$objcopyCmd"},
-			Description: "prefixSymbols $out",
 		},
 		"objcopyCmd", "prefix")
 
@@ -117,14 +109,12 @@ var (
 			Deps:        blueprint.DepsGCC,
 			Command:     "CROSS_COMPILE=$crossCompile $stripPath ${args} -i ${in} -o ${out} -d ${out}.d",
 			CommandDeps: []string{"$stripPath"},
-			Description: "strip $out",
 		},
 		"args", "crossCompile")
 
 	emptyFile = pctx.AndroidStaticRule("emptyFile",
 		blueprint.RuleParams{
-			Command:     "rm -f $out && touch $out",
-			Description: "empty file $out",
+			Command: "rm -f $out && touch $out",
 		})
 
 	_ = pctx.SourcePathVariable("copyGccLibPath", "build/soong/scripts/copygcclib.sh")
@@ -135,7 +125,6 @@ var (
 			Deps:        blueprint.DepsGCC,
 			Command:     "$copyGccLibPath $out $ccCmd $cFlags -print-file-name=${libName}",
 			CommandDeps: []string{"$copyGccLibPath", "$ccCmd"},
-			Description: "copy gcc $out",
 		},
 		"ccCmd", "cFlags", "libName")
 
@@ -155,7 +144,6 @@ var (
 		blueprint.RuleParams{
 			Command:     "rm -f $out && ${config.ClangBin}/clang-tidy $tidyFlags $in -- $cFlags && touch $out",
 			CommandDeps: []string{"${config.ClangBin}/clang-tidy"},
-			Description: "tidy $out",
 		},
 		"cFlags", "tidyFlags")
 
@@ -165,7 +153,6 @@ var (
 		blueprint.RuleParams{
 			Command:     "$yasmCmd $asFlags -o $out $in",
 			CommandDeps: []string{"$yasmCmd"},
-			Description: "yasm $out",
 		},
 		"asFlags")
 
@@ -175,7 +162,6 @@ var (
 		blueprint.RuleParams{
 			Command:     "rm -f $out && $sAbiDumper -o ${out} $in $exportDirs -- $cFlags -Wno-packed -Qunused-arguments -isystem ${config.RSIncludePath}",
 			CommandDeps: []string{"$sAbiDumper"},
-			Description: "header-abi-dumper $in -o $out $exportDirs",
 		},
 		"cFlags", "exportDirs")
 
@@ -185,7 +171,6 @@ var (
 		blueprint.RuleParams{
 			Command:        "$sAbiLinker -o ${out} $symbolFile -arch $arch -api $api $exportedHeaderFlags @${out}.rsp ",
 			CommandDeps:    []string{"$sAbiLinker"},
-			Description:    "header-abi-linker $in -o $out",
 			Rspfile:        "${out}.rsp",
 			RspfileContent: "${in}",
 		},
@@ -197,7 +182,6 @@ var (
 		blueprint.RuleParams{
 			Command:     "$sAbiDiffer -advice-only -o ${out} -new $in -old $referenceDump",
 			CommandDeps: []string{"$sAbiDiffer"},
-			Description: "header-abi-diff -o ${out} -new $in -old $referenceDump",
 		},
 		"referenceDump")
 )
@@ -323,10 +307,11 @@ func TransformSourceToObj(ctx android.ModuleContext, subdir string, srcFiles and
 
 		if srcFile.Ext() == ".asm" {
 			ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-				Rule:      yasm,
-				Output:    objFile,
-				Input:     srcFile,
-				OrderOnly: deps,
+				Rule:        yasm,
+				Description: "yasm " + srcFile.Rel(),
+				Output:      objFile,
+				Input:       srcFile,
+				OrderOnly:   deps,
 				Args: map[string]string{
 					"asFlags": flags.yasmFlags,
 				},
@@ -367,7 +352,11 @@ func TransformSourceToObj(ctx android.ModuleContext, subdir string, srcFiles and
 			default:
 				panic("unrecoginzied ccCmd")
 			}
+		}
+
+		ccDesc := ccCmd
 
+		if flags.clang {
 			ccCmd = "${config.ClangBin}/" + ccCmd
 		} else {
 			ccCmd = gccCmd(flags.toolchain, ccCmd)
@@ -382,6 +371,7 @@ func TransformSourceToObj(ctx android.ModuleContext, subdir string, srcFiles and
 
 		ctx.ModuleBuild(pctx, android.ModuleBuildParams{
 			Rule:            cc,
+			Description:     ccDesc + " " + srcFile.Rel(),
 			Output:          objFile,
 			ImplicitOutputs: implicitOutputs,
 			Input:           srcFile,
@@ -397,9 +387,10 @@ func TransformSourceToObj(ctx android.ModuleContext, subdir string, srcFiles and
 			tidyFiles = append(tidyFiles, tidyFile)
 
 			ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-				Rule:   clangTidy,
-				Output: tidyFile,
-				Input:  srcFile,
+				Rule:        clangTidy,
+				Description: "clang-tidy " + srcFile.Rel(),
+				Output:      tidyFile,
+				Input:       srcFile,
 				// We must depend on objFile, since clang-tidy doesn't
 				// support exporting dependencies.
 				Implicit: objFile,
@@ -415,10 +406,11 @@ func TransformSourceToObj(ctx android.ModuleContext, subdir string, srcFiles and
 			sAbiDumpFiles = append(sAbiDumpFiles, sAbiDumpFile)
 
 			ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-				Rule:     sAbiDump,
-				Output:   sAbiDumpFile,
-				Input:    srcFile,
-				Implicit: objFile,
+				Rule:        sAbiDump,
+				Description: "header-abi-dumper " + srcFile.Rel(),
+				Output:      sAbiDumpFile,
+				Input:       srcFile,
+				Implicit:    objFile,
 				Args: map[string]string{
 					"cFlags":     moduleCflags,
 					"exportDirs": flags.sAbiFlags,
@@ -452,10 +444,11 @@ func TransformObjToStaticLib(ctx android.ModuleContext, objFiles android.Paths,
 	}
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:      ar,
-		Output:    outputFile,
-		Inputs:    objFiles,
-		Implicits: deps,
+		Rule:        ar,
+		Description: "static link " + outputFile.Base(),
+		Output:      outputFile,
+		Inputs:      objFiles,
+		Implicits:   deps,
 		Args: map[string]string{
 			"arFlags": arFlags,
 			"arCmd":   arCmd,
@@ -477,24 +470,27 @@ func transformDarwinObjToStaticLib(ctx android.ModuleContext, objFiles android.P
 		dummyAr := android.PathForModuleOut(ctx, "dummy"+staticLibraryExtension)
 
 		ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-			Rule:      emptyFile,
-			Output:    dummy,
-			Implicits: deps,
+			Rule:        emptyFile,
+			Description: "empty object file",
+			Output:      dummy,
+			Implicits:   deps,
 		})
 
 		ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-			Rule:   darwinAr,
-			Output: dummyAr,
-			Input:  dummy,
+			Rule:        darwinAr,
+			Description: "empty static archive",
+			Output:      dummyAr,
+			Input:       dummy,
 			Args: map[string]string{
 				"arFlags": arFlags,
 			},
 		})
 
 		ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-			Rule:   darwinAppendAr,
-			Output: outputFile,
-			Input:  dummy,
+			Rule:        darwinAppendAr,
+			Description: "static link " + outputFile.Base(),
+			Output:      outputFile,
+			Input:       dummy,
 			Args: map[string]string{
 				"arFlags": "d",
 				"inAr":    dummyAr.String(),
@@ -519,10 +515,11 @@ func transformDarwinObjToStaticLib(ctx android.ModuleContext, objFiles android.P
 		}
 
 		build := android.ModuleBuildParams{
-			Rule:      darwinAr,
-			Output:    out,
-			Inputs:    l,
-			Implicits: deps,
+			Rule:        darwinAr,
+			Description: "static link " + out.Base(),
+			Output:      out,
+			Inputs:      l,
+			Implicits:   deps,
 			Args: map[string]string{
 				"arFlags": arFlags,
 			},
@@ -592,10 +589,11 @@ func TransformObjToDynamicBinary(ctx android.ModuleContext,
 	}
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:      ld,
-		Output:    outputFile,
-		Inputs:    objFiles,
-		Implicits: deps,
+		Rule:        ld,
+		Description: "link " + outputFile.Base(),
+		Output:      outputFile,
+		Inputs:      objFiles,
+		Implicits:   deps,
 		Args: map[string]string{
 			"ldCmd":    ldCmd,
 			"crtBegin": crtBegin.String(),
@@ -618,10 +616,11 @@ func TransformDumpToLinkedDump(ctx android.ModuleContext, sAbiDumps android.Path
 		linkedDumpDep = symbolFile.Path()
 	}
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:     sAbiLink,
-		Output:   outputFile,
-		Inputs:   sAbiDumps,
-		Implicit: linkedDumpDep,
+		Rule:        sAbiLink,
+		Description: "header-abi-linker " + outputFile.Base(),
+		Output:      outputFile,
+		Inputs:      sAbiDumps,
+		Implicit:    linkedDumpDep,
 		Args: map[string]string{
 			"symbolFile": symbolFileStr,
 			"arch":       ctx.Arch().ArchType.Name,
@@ -636,10 +635,11 @@ func SourceAbiDiff(ctx android.ModuleContext, inputDump android.Path, referenceD
 	baseName string) android.OptionalPath {
 	outputFile := android.PathForModuleOut(ctx, baseName+".abidiff")
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:     sAbiDiff,
-		Output:   outputFile,
-		Input:    inputDump,
-		Implicit: referenceDump,
+		Rule:        sAbiDiff,
+		Description: "header-abi-diff " + outputFile.Base(),
+		Output:      outputFile,
+		Input:       inputDump,
+		Implicit:    referenceDump,
 		Args: map[string]string{
 			"referenceDump": referenceDump.String(),
 		},
@@ -654,9 +654,10 @@ func TransformSharedObjectToToc(ctx android.ModuleContext, inputFile android.Wri
 	crossCompile := gccCmd(flags.toolchain, "")
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   toc,
-		Output: outputFile,
-		Input:  inputFile,
+		Rule:        toc,
+		Description: "generate toc " + inputFile.Base(),
+		Output:      outputFile,
+		Input:       inputFile,
 		Args: map[string]string{
 			"crossCompile": crossCompile,
 		},
@@ -675,9 +676,10 @@ func TransformObjsToObj(ctx android.ModuleContext, objFiles android.Paths,
 	}
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   partialLd,
-		Output: outputFile,
-		Inputs: objFiles,
+		Rule:        partialLd,
+		Description: "link " + outputFile.Base(),
+		Output:      outputFile,
+		Inputs:      objFiles,
 		Args: map[string]string{
 			"ldCmd":   ldCmd,
 			"ldFlags": flags.ldFlags,
@@ -692,9 +694,10 @@ func TransformBinaryPrefixSymbols(ctx android.ModuleContext, prefix string, inpu
 	objcopyCmd := gccCmd(flags.toolchain, "objcopy")
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   prefixSymbols,
-		Output: outputFile,
-		Input:  inputFile,
+		Rule:        prefixSymbols,
+		Description: "prefix symbols " + outputFile.Base(),
+		Output:      outputFile,
+		Input:       inputFile,
 		Args: map[string]string{
 			"objcopyCmd": objcopyCmd,
 			"prefix":     prefix,
@@ -718,9 +721,10 @@ func TransformStrip(ctx android.ModuleContext, inputFile android.Path,
 	}
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   strip,
-		Output: outputFile,
-		Input:  inputFile,
+		Rule:        strip,
+		Description: "strip " + outputFile.Base(),
+		Output:      outputFile,
+		Input:       inputFile,
 		Args: map[string]string{
 			"crossCompile": crossCompile,
 			"args":         args,
@@ -732,9 +736,10 @@ func TransformDarwinStrip(ctx android.ModuleContext, inputFile android.Path,
 	outputFile android.WritablePath) {
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   darwinStrip,
-		Output: outputFile,
-		Input:  inputFile,
+		Rule:        darwinStrip,
+		Description: "strip " + outputFile.Base(),
+		Output:      outputFile,
+		Input:       inputFile,
 	})
 }
 
@@ -756,8 +761,9 @@ func CopyGccLib(ctx android.ModuleContext, libName string,
 	flags builderFlags, outputFile android.WritablePath) {
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   copyGccLib,
-		Output: outputFile,
+		Rule:        copyGccLib,
+		Description: "copy gcc library " + libName,
+		Output:      outputFile,
 		Args: map[string]string{
 			"ccCmd":   gccCmd(flags.toolchain, "gcc"),
 			"cFlags":  flags.globalFlags,
diff --git a/cc/gen.go b/cc/gen.go
index 353c43d8..7a22abdd 100644
--- a/cc/gen.go
+++ b/cc/gen.go
@@ -37,7 +37,6 @@ var (
 		blueprint.RuleParams{
 			Command:     "BISON_PKGDATADIR=$yaccDataDir $yaccCmd -d $yaccFlags --defines=$hFile -o $out $in",
 			CommandDeps: []string{"$yaccCmd"},
-			Description: "yacc $out",
 		},
 		"yaccFlags", "hFile")
 
@@ -45,7 +44,6 @@ var (
 		blueprint.RuleParams{
 			Command:     "$lexCmd -o$out $in",
 			CommandDeps: []string{"$lexCmd"},
-			Description: "lex $out",
 		})
 
 	aidl = pctx.AndroidStaticRule("aidl",
@@ -54,7 +52,6 @@ var (
 			CommandDeps: []string{"$aidlCmd"},
 			Depfile:     "${out}.d",
 			Deps:        blueprint.DepsGCC,
-			Description: "aidl $out",
 		},
 		"aidlFlags", "outDir")
 )
@@ -64,6 +61,7 @@ func genYacc(ctx android.ModuleContext, yaccFile android.Path, outFile android.M
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
 		Rule:           yacc,
+		Description:    "yacc " + yaccFile.Rel(),
 		Output:         outFile,
 		ImplicitOutput: headerFile,
 		Input:          yaccFile,
@@ -79,9 +77,10 @@ func genYacc(ctx android.ModuleContext, yaccFile android.Path, outFile android.M
 func genAidl(ctx android.ModuleContext, aidlFile android.Path, outFile android.ModuleGenPath, aidlFlags string) android.Paths {
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   aidl,
-		Output: outFile,
-		Input:  aidlFile,
+		Rule:        aidl,
+		Description: "aidl " + aidlFile.Rel(),
+		Output:      outFile,
+		Input:       aidlFile,
 		Args: map[string]string{
 			"aidlFlags": aidlFlags,
 			"outDir":    android.PathForModuleGen(ctx, "aidl").String(),
@@ -94,9 +93,10 @@ func genAidl(ctx android.ModuleContext, aidlFile android.Path, outFile android.M
 
 func genLex(ctx android.ModuleContext, lexFile android.Path, outFile android.ModuleGenPath) {
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   lex,
-		Output: outFile,
-		Input:  lexFile,
+		Rule:        lex,
+		Description: "lex " + lexFile.Rel(),
+		Output:      outFile,
+		Input:       lexFile,
 	})
 }
 
diff --git a/cc/ndk_headers.go b/cc/ndk_headers.go
index deb735a9..516f6e20 100644
--- a/cc/ndk_headers.go
+++ b/cc/ndk_headers.go
@@ -31,7 +31,6 @@ var (
 			// let us have only implicit outputs.
 			Command:     "$versionerCmd -o $outDir $srcDir $depsPath && touch $out",
 			CommandDeps: []string{"$versionerCmd"},
-			Description: "versioner preprocess $in",
 		},
 		"depsPath", "srcDir", "outDir")
 )
@@ -238,6 +237,7 @@ func processHeadersWithVersioner(ctx android.ModuleContext, srcDir, outDir andro
 	timestampFile := android.PathForModuleOut(ctx, "versioner.timestamp")
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
 		Rule:            preprocessBionicHeaders,
+		Description:     "versioner preprocess " + srcDir.Rel(),
 		Output:          timestampFile,
 		Implicits:       append(srcFiles, depsGlob...),
 		ImplicitOutputs: installPaths,
diff --git a/cc/ndk_library.go b/cc/ndk_library.go
index 1bd63a98..ba3ec7d2 100644
--- a/cc/ndk_library.go
+++ b/cc/ndk_library.go
@@ -32,7 +32,6 @@ var (
 		blueprint.RuleParams{
 			Command: "$toolPath --arch $arch --api $apiLevel --api-map " +
 				"$apiMap $vndk $in $out",
-			Description: "genStubSrc $out",
 			CommandDeps: []string{"$toolPath"},
 		}, "arch", "apiLevel", "apiMap", "vndk")
 
@@ -251,10 +250,11 @@ func compileStubLibrary(ctx ModuleContext, flags Flags, symbolFile, apiLevel, vn
 	symbolFilePath := android.PathForModuleSrc(ctx, symbolFile)
 	apiLevelsJson := android.GetApiLevelsJson(ctx)
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:      genStubSrc,
-		Outputs:   []android.WritablePath{stubSrcPath, versionScriptPath},
-		Input:     symbolFilePath,
-		Implicits: []android.Path{apiLevelsJson},
+		Rule:        genStubSrc,
+		Description: "generate stubs " + symbolFilePath.Rel(),
+		Outputs:     []android.WritablePath{stubSrcPath, versionScriptPath},
+		Input:       symbolFilePath,
+		Implicits:   []android.Path{apiLevelsJson},
 		Args: map[string]string{
 			"arch":     arch,
 			"apiLevel": apiLevel,
diff --git a/cc/ndk_sysroot.go b/cc/ndk_sysroot.go
index 2e4e3959..5b4cfbe8 100644
--- a/cc/ndk_sysroot.go
+++ b/cc/ndk_sysroot.go
@@ -113,10 +113,11 @@ func (n *ndkSingleton) GenerateBuildActions(ctx blueprint.SingletonContext) {
 
 	combinedLicense := getNdkInstallBase(ctx).Join(ctx, "NOTICE")
 	ctx.Build(pctx, blueprint.BuildParams{
-		Rule:     android.Cat,
-		Outputs:  []string{combinedLicense.String()},
-		Inputs:   licensePaths,
-		Optional: true,
+		Rule:        android.Cat,
+		Description: "combine licenses",
+		Outputs:     []string{combinedLicense.String()},
+		Inputs:      licensePaths,
+		Optional:    true,
 	})
 
 	depPaths := append(installPaths, combinedLicense.String())
diff --git a/cc/proto.go b/cc/proto.go
index 10d3c624..6c1789ab 100644
--- a/cc/proto.go
+++ b/cc/proto.go
@@ -30,7 +30,6 @@ var (
 		blueprint.RuleParams{
 			Command:     "$protocCmd --cpp_out=$outDir $protoFlags $in",
 			CommandDeps: []string{"$protocCmd"},
-			Description: "protoc $out",
 		}, "protoFlags", "outDir")
 )
 
@@ -48,9 +47,10 @@ func genProto(ctx android.ModuleContext, protoFile android.Path,
 	outFile := android.GenPathWithExt(ctx, "proto", protoFile, "pb.cc")
 	headerFile := android.GenPathWithExt(ctx, "proto", protoFile, "pb.h")
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:    proto,
-		Outputs: android.WritablePaths{outFile, headerFile},
-		Input:   protoFile,
+		Rule:        proto,
+		Description: "protoc " + protoFile.Rel(),
+		Outputs:     android.WritablePaths{outFile, headerFile},
+		Input:       protoFile,
 		Args: map[string]string{
 			"outDir":     protoDir(ctx).String(),
 			"protoFlags": protoFlags,
diff --git a/cc/relocation_packer.go b/cc/relocation_packer.go
index c509f312..c9f82ba8 100644
--- a/cc/relocation_packer.go
+++ b/cc/relocation_packer.go
@@ -30,7 +30,6 @@ var relocationPackerRule = pctx.AndroidStaticRule("packRelocations",
 	blueprint.RuleParams{
 		Command:     "rm -f $out && cp $in $out && $relocationPackerCmd $out",
 		CommandDeps: []string{"$relocationPackerCmd"},
-		Description: "pack relocations $out",
 	})
 
 type RelocationPackerProperties struct {
@@ -77,8 +76,9 @@ func (p *relocationPacker) needsPacking(ctx ModuleContext) bool {
 
 func (p *relocationPacker) pack(ctx ModuleContext, in, out android.ModuleOutPath, flags builderFlags) {
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   relocationPackerRule,
-		Output: out,
-		Input:  in,
+		Rule:        relocationPackerRule,
+		Description: "pack relocations",
+		Output:      out,
+		Input:       in,
 	})
 }
diff --git a/cc/rs.go b/cc/rs.go
index a001f89e..976107ea 100644
--- a/cc/rs.go
+++ b/cc/rs.go
@@ -39,7 +39,6 @@ var (
 			CommandDeps: []string{"$rsCmd"},
 			Depfile:     "${out}.d",
 			Deps:        blueprint.DepsGCC,
-			Description: "rsCpp $out",
 		},
 		"depFiles", "outDir", "rsFlags", "stampFile")
 )
@@ -67,6 +66,7 @@ func rsGenerateCpp(ctx android.ModuleContext, rsFiles android.Paths, rsFlags str
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
 		Rule:            rsCpp,
+		Description:     "llvm-rs-cc",
 		Output:          stampFile,
 		ImplicitOutputs: cppFiles,
 		Inputs:          rsFiles,
diff --git a/genrule/genrule.go b/genrule/genrule.go
index 68077616..2ff018f5 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -218,11 +218,17 @@ func (g *generator) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 }
 
 func (g *generator) generateSourceFile(ctx android.ModuleContext, task generateTask) {
+	desc := "generate"
+	if len(task.out) == 1 {
+		desc += " " + task.out[0].Base()
+	}
+
 	params := android.ModuleBuildParams{
-		Rule:      g.rule,
-		Outputs:   task.out,
-		Inputs:    task.in,
-		Implicits: g.deps,
+		Rule:        g.rule,
+		Description: "generate",
+		Outputs:     task.out,
+		Inputs:      task.in,
+		Implicits:   g.deps,
 	}
 	if g.properties.Depfile {
 		depfile := android.GenPathWithExt(ctx, "", task.out[0], task.out[0].Ext()+".d")
diff --git a/java/app_builder.go b/java/app_builder.go
index bbd3dac4..55fded57 100644
--- a/java/app_builder.go
+++ b/java/app_builder.go
@@ -34,7 +34,6 @@ var (
 				`-J $javaDir || ( rm -rf "$javaDir/*"; exit 41 ) && ` +
 				`find $javaDir -name "*.java" > $javaFileList`,
 			CommandDeps: []string{"$aaptCmd"},
-			Description: "aapt create R.java $out",
 		},
 		"aaptFlags", "publicResourcesFile", "proguardOptionsFile", "javaDir", "javaFileList")
 
@@ -42,7 +41,6 @@ var (
 		blueprint.RuleParams{
 			Command:     `rm -f $out && $aaptCmd package $aaptFlags -F $out`,
 			CommandDeps: []string{"$aaptCmd"},
-			Description: "aapt export package $out",
 		},
 		"aaptFlags", "publicResourcesFile", "proguardOptionsFile", "javaDir", "javaFileList")
 
@@ -51,7 +49,6 @@ var (
 			// TODO: add-jni-shared-libs-to-package
 			Command:     `cp -f $in $out.tmp && $aaptCmd package -u $aaptFlags -F $out.tmp && mv $out.tmp $out`,
 			CommandDeps: []string{"$aaptCmd"},
-			Description: "aapt package $out",
 		},
 		"aaptFlags")
 
@@ -59,7 +56,6 @@ var (
 		blueprint.RuleParams{
 			Command:     `java -jar $signapkCmd $certificates $in $out`,
 			CommandDeps: []string{"$signapkCmd"},
-			Description: "signapk $out",
 		},
 		"certificates")
 
@@ -68,7 +64,7 @@ var (
 			Command: "java -classpath $androidManifestMergerCmd com.android.manifmerger.Main merge " +
 				"--main $in --libs $libsManifests --out $out",
 			CommandDeps: []string{"$androidManifestMergerCmd"},
-			Description: "merge manifest files $out",
+			Description: "merge manifest files",
 		},
 		"libsManifests")
 )
@@ -87,9 +83,10 @@ func CreateResourceJavaFiles(ctx android.ModuleContext, flags []string,
 	proguardOptionsFile := android.PathForModuleOut(ctx, "proguard.options")
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:      aaptCreateResourceJavaFile,
-		Outputs:   android.WritablePaths{publicResourcesFile, proguardOptionsFile, javaFileList},
-		Implicits: deps,
+		Rule:        aaptCreateResourceJavaFile,
+		Description: "aapt create R.java",
+		Outputs:     android.WritablePaths{publicResourcesFile, proguardOptionsFile, javaFileList},
+		Implicits:   deps,
 		Args: map[string]string{
 			"aaptFlags":           strings.Join(flags, " "),
 			"publicResourcesFile": publicResourcesFile.String(),
@@ -106,9 +103,10 @@ func CreateExportPackage(ctx android.ModuleContext, flags []string, deps android
 	outputFile := android.PathForModuleOut(ctx, "package-export.apk")
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:      aaptCreateAssetsPackage,
-		Output:    outputFile,
-		Implicits: deps,
+		Rule:        aaptCreateAssetsPackage,
+		Description: "aapt export package",
+		Output:      outputFile,
+		Implicits:   deps,
 		Args: map[string]string{
 			"aaptFlags": strings.Join(flags, " "),
 		},
@@ -123,9 +121,10 @@ func CreateAppPackage(ctx android.ModuleContext, flags []string, jarFile android
 	resourceApk := android.PathForModuleOut(ctx, "resources.apk")
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   aaptAddResources,
-		Output: resourceApk,
-		Input:  jarFile,
+		Rule:        aaptAddResources,
+		Description: "aapt package",
+		Output:      resourceApk,
+		Input:       jarFile,
 		Args: map[string]string{
 			"aaptFlags": strings.Join(flags, " "),
 		},
@@ -139,9 +138,10 @@ func CreateAppPackage(ctx android.ModuleContext, flags []string, jarFile android
 	}
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   signapk,
-		Output: outputFile,
-		Input:  resourceApk,
+		Rule:        signapk,
+		Description: "signapk",
+		Output:      outputFile,
+		Input:       resourceApk,
 		Args: map[string]string{
 			"certificates": strings.Join(certificateArgs, " "),
 		},
diff --git a/java/builder.go b/java/builder.go
index a9da0fc0..895a9994 100644
--- a/java/builder.go
+++ b/java/builder.go
@@ -45,7 +45,6 @@ var (
 				`find $outDir -name "*.class" > $out`,
 			Rspfile:        "$out.rsp",
 			RspfileContent: "$in",
-			Description:    "javac $outDir",
 		},
 		"javacCmd", "javacFlags", "bootClasspath", "classpath", "outDir")
 
@@ -53,7 +52,6 @@ var (
 		blueprint.RuleParams{
 			Command:     `$jarCmd -o $out $jarArgs`,
 			CommandDeps: []string{"$jarCmd"},
-			Description: "jar $out",
 		},
 		"jarCmd", "jarArgs")
 
@@ -63,7 +61,6 @@ var (
 				`$dxCmd --dex --output=$outDir $dxFlags $in || ( rm -rf "$outDir"; exit 41 ) && ` +
 				`find "$outDir" -name "classes*.dex" > $out`,
 			CommandDeps: []string{"$dxCmd"},
-			Description: "dex $out",
 		},
 		"outDir", "dxFlags")
 
@@ -71,7 +68,6 @@ var (
 		blueprint.RuleParams{
 			Command:     "java -jar $jarjarCmd process $rulesFile $in $out",
 			CommandDeps: []string{"$jarjarCmd", "$rulesFile"},
-			Description: "jarjar $out",
 		},
 		"rulesFile")
 
@@ -81,7 +77,6 @@ var (
 				`find $outDir -name "*.class" > $classFile && ` +
 				`find $outDir -type f -a \! -name "*.class" -a \! -name "MANIFEST.MF" > $resourceFile || ` +
 				`(rm -rf $outDir; exit 42)`,
-			Description: "extract java prebuilt $outDir",
 		},
 		"outDir", "classFile", "resourceFile")
 )
@@ -122,10 +117,11 @@ func TransformJavaToClasses(ctx android.ModuleContext, srcFiles android.Paths, s
 	deps = append(deps, srcFileLists...)
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:      javac,
-		Output:    classFileList,
-		Inputs:    srcFiles,
-		Implicits: deps,
+		Rule:        javac,
+		Description: "javac",
+		Output:      classFileList,
+		Inputs:      srcFiles,
+		Implicits:   deps,
 		Args: map[string]string{
 			"javacFlags":    javacFlags,
 			"bootClasspath": flags.bootClasspath,
@@ -156,9 +152,10 @@ func TransformClassesToJar(ctx android.ModuleContext, classes []jarSpec,
 	}
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:      jar,
-		Output:    outputFile,
-		Implicits: deps,
+		Rule:        jar,
+		Description: "jar",
+		Output:      outputFile,
+		Implicits:   deps,
 		Args: map[string]string{
 			"jarArgs": strings.Join(jarArgs, " "),
 		},
@@ -174,9 +171,10 @@ func TransformClassesJarToDex(ctx android.ModuleContext, classesJar android.Path
 	outputFile := android.PathForModuleOut(ctx, "dex.filelist")
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   dx,
-		Output: outputFile,
-		Input:  classesJar,
+		Rule:        dx,
+		Description: "dx",
+		Output:      outputFile,
+		Input:       classesJar,
 		Args: map[string]string{
 			"dxFlags": flags.dxFlags,
 			"outDir":  outDir.String(),
@@ -202,9 +200,10 @@ func TransformDexToJavaLib(ctx android.ModuleContext, resources []jarSpec,
 	jarArgs = append(jarArgs, dexJarSpec.soongJarArgs())
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:      jar,
-		Output:    outputFile,
-		Implicits: deps,
+		Rule:        jar,
+		Description: "jar",
+		Output:      outputFile,
+		Implicits:   deps,
 		Args: map[string]string{
 			"jarArgs": strings.Join(jarArgs, " "),
 		},
@@ -216,10 +215,11 @@ func TransformDexToJavaLib(ctx android.ModuleContext, resources []jarSpec,
 func TransformJarJar(ctx android.ModuleContext, classesJar android.Path, rulesFile android.Path) android.Path {
 	outputFile := android.PathForModuleOut(ctx, "classes-jarjar.jar")
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:     jarjar,
-		Output:   outputFile,
-		Input:    classesJar,
-		Implicit: rulesFile,
+		Rule:        jarjar,
+		Description: "jarjar",
+		Output:      outputFile,
+		Input:       classesJar,
+		Implicit:    rulesFile,
 		Args: map[string]string{
 			"rulesFile": rulesFile.String(),
 		},
@@ -236,9 +236,10 @@ func TransformPrebuiltJarToClasses(ctx android.ModuleContext,
 	resourceFileList := android.PathForModuleOut(ctx, "extracted/resources.list")
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:    extractPrebuilt,
-		Outputs: android.WritablePaths{classFileList, resourceFileList},
-		Input:   prebuilt,
+		Rule:        extractPrebuilt,
+		Description: "extract classes",
+		Outputs:     android.WritablePaths{classFileList, resourceFileList},
+		Input:       prebuilt,
 		Args: map[string]string{
 			"outDir":       classDir.String(),
 			"classFile":    classFileList.String(),
diff --git a/java/gen.go b/java/gen.go
index 06247085..e3973bf8 100644
--- a/java/gen.go
+++ b/java/gen.go
@@ -37,7 +37,6 @@ var (
 		blueprint.RuleParams{
 			Command:     "$aidlCmd -d$depFile $aidlFlags $in $out",
 			CommandDeps: []string{"$aidlCmd"},
-			Description: "aidl $out",
 		},
 		"depFile", "aidlFlags")
 
@@ -45,14 +44,12 @@ var (
 		blueprint.RuleParams{
 			Command:     "$logtagsCmd -o $out $in $allLogtagsFile",
 			CommandDeps: []string{"$logtagsCmd"},
-			Description: "logtags $out",
 		})
 
 	mergeLogtags = pctx.AndroidStaticRule("mergeLogtags",
 		blueprint.RuleParams{
 			Command:     "$mergeLogtagsCmd -o $out $in",
 			CommandDeps: []string{"$mergeLogtagsCmd"},
-			Description: "merge logtags $out",
 		})
 )
 
@@ -61,9 +58,10 @@ func genAidl(ctx android.ModuleContext, aidlFile android.Path, aidlFlags string)
 	depFile := javaFile.String() + ".d"
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   aidl,
-		Output: javaFile,
-		Input:  aidlFile,
+		Rule:        aidl,
+		Description: "aidl " + aidlFile.Rel(),
+		Output:      javaFile,
+		Input:       aidlFile,
 		Args: map[string]string{
 			"depFile":   depFile,
 			"aidlFlags": aidlFlags,
@@ -77,9 +75,10 @@ func genLogtags(ctx android.ModuleContext, logtagsFile android.Path) android.Pat
 	javaFile := android.GenPathWithExt(ctx, "logtags", logtagsFile, "java")
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:   logtags,
-		Output: javaFile,
-		Input:  logtagsFile,
+		Rule:        logtags,
+		Description: "logtags " + logtagsFile.Rel(),
+		Output:      javaFile,
+		Input:       logtagsFile,
 	})
 
 	return javaFile
@@ -122,8 +121,9 @@ func (l *logtagsSingleton) GenerateBuildActions(ctx blueprint.SingletonContext)
 	})
 
 	ctx.Build(pctx, blueprint.BuildParams{
-		Rule:    mergeLogtags,
-		Outputs: []string{"$allLogtagsFile"},
-		Inputs:  allLogtags.Strings(),
+		Rule:        mergeLogtags,
+		Description: "merge logtags",
+		Outputs:     []string{"$allLogtagsFile"},
+		Inputs:      allLogtags.Strings(),
 	})
 }
diff --git a/python/builder.go b/python/builder.go
index 62234486..541d2bf0 100644
--- a/python/builder.go
+++ b/python/builder.go
@@ -35,7 +35,6 @@ var (
 				`$parCmd -o $parFile $parArgs && echo '#!/usr/bin/env python' | cat - $parFile > $out && ` +
 				`chmod +x $out && (rm -f $initFile; rm -f $stub; rm -f $parFile)`,
 			CommandDeps: []string{"$parCmd", "$template"},
-			Description: "build par $out",
 		},
 		"initFile", "interp", "main", "template", "stub", "parCmd", "parFile", "parArgs")
 )
@@ -78,9 +77,10 @@ func registerBuildActionForModuleFileList(ctx android.ModuleContext,
 	}
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:      android.WriteFile,
-		Output:    fileList,
-		Implicits: files,
+		Rule:        android.WriteFile,
+		Description: "generate " + fileList.Rel(),
+		Output:      fileList,
+		Implicits:   files,
 		Args: map[string]string{
 			"content": strings.Join(content, "\n"),
 		},
@@ -126,9 +126,10 @@ func registerBuildActionForParFile(ctx android.ModuleContext,
 	}
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
-		Rule:      par,
-		Output:    binFile,
-		Implicits: implicits,
+		Rule:        par,
+		Description: "python archive",
+		Output:      binFile,
+		Implicits:   implicits,
 		Args: map[string]string{
 			"initFile": initFile,
 			// the "\" isn't being interpreted by regex parser, it's being