goose: refactor *gen.inject

The function had grown too long. Several related cleanups:

- Factored out the function return value logic, which had been
  duplicated between providers and injectors.
- Moved code generation for different provider call types into separate
  functions. This moves injector-specific state to a new type
  injectorGen to keep the parameter count down.
- Since it's infeasible to keep the "shadow pass" collecting import
  identifiers in sync the spread out logic, the injector code
  generation is just run twice, with initial output discarded.
- Removed the zero value logic left over from Optional.

Reviewed-by: Tuo Shan <shantuo@google.com>

internal/goose/analyze.go

@@ -48,9 +48,8 @@ type call struct {
 	name       string
 
 	// args is a list of arguments to call the provider with.  Each element is:
-	// a) one of the givens (args[i] < len(given)),
-	// b) the result of a previous provider call (args[i] >= len(given)), or
-	// c) the zero value for the type (args[i] == -1).
+	// a) one of the givens (args[i] < len(given)), or
+	// b) the result of a previous provider call (args[i] >= len(given))
 	//
 	// This will be nil for kind == valueExpr.
 	args []int

internal/goose/goose.go

@@ -108,7 +108,7 @@ func generateInjectors(g *gen, pkgInfo *loader.PackageInfo) (injectorFiles []*as
 				return nil, fmt.Errorf("%v: %v", g.prog.Fset.Position(fn.Pos()), err)
 			}
 			sig := pkgInfo.ObjectOf(fn.Name).Type().(*types.Signature)
-			if err := g.inject(g.prog.Fset, fn.Name.Name, sig, set); err != nil {
+			if err := g.inject(fn.Name.Name, sig, set); err != nil {
 				return nil, fmt.Errorf("%v: %v", g.prog.Fset.Position(fn.Pos()), err)
 			}
 		}
@@ -140,18 +140,18 @@ func copyNonInjectorDecls(g *gen, files []*ast.File, info *types.Info) {
 				first = false
 			}
 			// TODO(light): Add line number at top of each declaration.
-			g.writeAST(g.prog.Fset, info, decl)
+			g.writeAST(info, decl)
 			g.p("\n\n")
 		}
 	}
 }
 
-// gen is the generator state.
+// gen is the file-wide generator state.
 type gen struct {
 	currPackage string
 	buf         bytes.Buffer
 	imports     map[string]string
-	prog        *loader.Program // for determining package names
+	prog        *loader.Program // for positions and determining package names
 }
 
 func newGen(prog *loader.Program, pkg string) *gen {
@@ -190,237 +190,54 @@ func (g *gen) frame() []byte {
 }
 
 // inject emits the code for an injector.
-func (g *gen) inject(fset *token.FileSet, name string, sig *types.Signature, set *ProviderSet) error {
-	results := sig.Results()
-	var returnsCleanup, returnsErr bool
-	switch results.Len() {
-	case 0:
-		return fmt.Errorf("inject %s: no return values", name)
-	case 1:
-		returnsCleanup, returnsErr = false, false
-	case 2:
-		switch t := results.At(1).Type(); {
-		case types.Identical(t, errorType):
-			returnsCleanup, returnsErr = false, true
-		case types.Identical(t, cleanupType):
-			returnsCleanup, returnsErr = true, false
-		default:
-			return fmt.Errorf("inject %s: second return type is %s; must be error or func()", name, types.TypeString(t, nil))
+func (g *gen) inject(name string, sig *types.Signature, set *ProviderSet) error {
+	injectSig, err := funcOutput(sig)
+	if err != nil {
+		return fmt.Errorf("inject %s: %v", name, err)
 	}
-	case 3:
-		if t := results.At(1).Type(); !types.Identical(t, cleanupType) {
-			return fmt.Errorf("inject %s: second return type is %s; must be func()", name, types.TypeString(t, nil))
-		}
-		if t := results.At(2).Type(); !types.Identical(t, errorType) {
-			return fmt.Errorf("inject %s: third return type is %s; must be error", name, types.TypeString(t, nil))
-		}
-		returnsCleanup, returnsErr = true, true
-	default:
-		return fmt.Errorf("inject %s: too many return values", name)
-	}
-	outType := results.At(0).Type()
 	params := sig.Params()
 	given := make([]types.Type, params.Len())
 	for i := 0; i < params.Len(); i++ {
 		given[i] = params.At(i).Type()
 	}
-	calls, err := solve(fset, outType, given, set)
+	calls, err := solve(g.prog.Fset, injectSig.out, given, set)
 	if err != nil {
 		return err
 	}
 	for i := range calls {
-		if calls[i].hasCleanup && !returnsCleanup {
-			return fmt.Errorf("inject %s: provider for %s returns cleanup but injection does not return cleanup function", name, types.TypeString(calls[i].out, nil))
+		c := &calls[i]
+		if c.hasCleanup && !injectSig.cleanup {
+			return fmt.Errorf("inject %s: provider for %s returns cleanup but injection does not return cleanup function", name, types.TypeString(c.out, nil))
 		}
-		if calls[i].hasErr && !returnsErr {
-			return fmt.Errorf("inject %s: provider for %s returns error but injection not allowed to fail", name, types.TypeString(calls[i].out, nil))
+		if c.hasErr && !injectSig.err {
+			return fmt.Errorf("inject %s: provider for %s returns error but injection not allowed to fail", name, types.TypeString(c.out, nil))
 		}
-	}
-
-	// Prequalify all types.  Since import disambiguation ignores local
-	// variables, it takes precedence.
-	paramTypes := make([]string, params.Len())
-	for i := 0; i < params.Len(); i++ {
-		paramTypes[i] = types.TypeString(params.At(i).Type(), g.qualifyPkg)
-	}
-	for _, c := range calls {
-		switch c.kind {
-		case funcProviderCall:
-			g.qualifyImport(c.importPath)
-			for i := range c.args {
-				if c.args[i] == -1 {
-					zeroValue(c.ins[i], g.qualifyPkg)
-				}
-			}
-		case structProvider:
-			g.qualifyImport(c.importPath)
-		case valueExpr:
+		if c.kind == valueExpr {
 			if err := accessibleFrom(c.valueTypeInfo, c.valueExpr, g.currPackage); err != nil {
 				// TODO(light): Display line number of value expression.
 				ts := types.TypeString(c.out, nil)
 				return fmt.Errorf("inject %s: value %s can't be used: %v", name, ts, err)
 			}
-		default:
-			panic("unknown kind")
 		}
 	}
-	outTypeString := types.TypeString(outType, g.qualifyPkg)
-	zv := zeroValue(outType, g.qualifyPkg)
-	// Set up local variables.
-	paramNames := make([]string, params.Len())
-	localNames := make([]string, len(calls))
-	cleanupNames := make([]string, len(calls))
-	errVar := disambiguate("err", g.nameInFileScope)
-	collides := func(v string) bool {
-		if v == errVar {
-			return true
-		}
-		for _, a := range paramNames {
-			if a == v {
-				return true
-			}
-		}
-		for _, l := range localNames {
-			if l == v {
-				return true
-			}
-		}
-		for _, l := range cleanupNames {
-			if l == v {
-				return true
-			}
-		}
-		return g.nameInFileScope(v)
-	}
 
-	g.p("func %s(", name)
-	for i := 0; i < params.Len(); i++ {
-		if i > 0 {
-			g.p(", ")
-		}
-		pi := params.At(i)
-		a := pi.Name()
-		if a == "" || a == "_" {
-			a = typeVariableName(pi.Type())
-			if a == "" {
-				a = "arg"
-			}
-		}
-		paramNames[i] = disambiguate(a, collides)
-		g.p("%s %s", paramNames[i], paramTypes[i])
-	}
-	if returnsCleanup && returnsErr {
-		g.p(") (%s, func(), error) {\n", outTypeString)
-	} else if returnsCleanup {
-		g.p(") (%s, func()) {\n", outTypeString)
-	} else if returnsErr {
-		g.p(") (%s, error) {\n", outTypeString)
-	} else {
-		g.p(") %s {\n", outTypeString)
-	}
-	for i := range calls {
-		c := &calls[i]
-		lname := typeVariableName(c.out)
-		if lname == "" {
-			lname = "v"
-		}
-		lname = disambiguate(lname, collides)
-		localNames[i] = lname
-		g.p("\t%s", lname)
-		if c.hasCleanup {
-			cleanupNames[i] = disambiguate("cleanup", collides)
-			g.p(", %s", cleanupNames[i])
-		}
-		if c.hasErr {
-			g.p(", %s", errVar)
-		}
-		g.p(" := ")
-		switch c.kind {
-		case structProvider:
-			if _, ok := c.out.(*types.Pointer); ok {
-				g.p("&")
-			}
-			g.p("%s{\n", g.qualifiedID(c.importPath, c.name))
-			for j, a := range c.args {
-				if a == -1 {
-					// Omit zero value fields from composite literal.
-					continue
-				}
-				g.p("\t\t%s: ", c.fieldNames[j])
-				if a < params.Len() {
-					g.p("%s", paramNames[a])
-				} else {
-					g.p("%s", localNames[a-params.Len()])
-				}
-				g.p(",\n")
-			}
-			g.p("\t}\n")
-		case funcProviderCall:
-			g.p("%s(", g.qualifiedID(c.importPath, c.name))
-			for j, a := range c.args {
-				if j > 0 {
-					g.p(", ")
-				}
-				if a == -1 {
-					g.p("%s", zeroValue(c.ins[j], g.qualifyPkg))
-				} else if a < params.Len() {
-					g.p("%s", paramNames[a])
-				} else {
-					g.p("%s", localNames[a-params.Len()])
-				}
-			}
-			g.p(")\n")
-		case valueExpr:
-			g.writeAST(fset, c.valueTypeInfo, c.valueExpr)
-			g.p("\n")
-		default:
-			panic("unknown kind")
-		}
-		if c.hasErr {
-			g.p("\tif %s != nil {\n", errVar)
-			for j := i - 1; j >= 0; j-- {
-				if calls[j].hasCleanup {
-					g.p("\t\t%s()\n", cleanupNames[j])
-				}
-			}
-			g.p("\t\treturn %s", zv)
-			if returnsCleanup {
-				g.p(", nil")
-			}
-			// TODO(light): Give information about failing provider.
-			g.p(", err\n")
-			g.p("\t}\n")
-		}
-	}
-	if len(calls) == 0 {
-		for i := range given {
-			if types.Identical(outType, given[i]) {
-				g.p("\treturn %s", paramNames[i])
-				break
-			}
-		}
-	} else {
-		g.p("\treturn %s", localNames[len(calls)-1])
-	}
-	if returnsCleanup {
-		g.p(", func() {\n")
-		for i := len(calls) - 1; i >= 0; i-- {
-			if calls[i].hasCleanup {
-				g.p("\t\t%s()\n", cleanupNames[i])
-			}
-		}
-		g.p("\t}")
-	}
-	if returnsErr {
-		g.p(", nil")
-	}
-	g.p("\n}\n\n")
+	// Perform one pass to collect all imports, followed by the real pass.
+	injectPass(name, params, injectSig, calls, &injectorGen{
+		g:       g,
+		errVar:  disambiguate("err", g.nameInFileScope),
+		discard: true,
+	})
+	injectPass(name, params, injectSig, calls, &injectorGen{
+		g:       g,
+		errVar:  disambiguate("err", g.nameInFileScope),
+		discard: false,
+	})
 	return nil
 }
 
-// writeAST prints an AST node into the generated output, rewriting any
-// package references it encounters.
-func (g *gen) writeAST(fset *token.FileSet, info *types.Info, node ast.Node) {
+// rewritePkgRefs rewrites any package references in an AST into references for the
+// generated package.
+func (g *gen) rewritePkgRefs(info *types.Info, node ast.Node) ast.Node {
 	start, end := node.Pos(), node.End()
 	node = copyAST(node)
 	// First, rewrite all package names. This lets us know all the
@@ -500,7 +317,7 @@ func (g *gen) writeAST(fset *token.FileSet, info *types.Info, node ast.Node) {
 			return true
 		}
 
-		// Rename any symbols defined within writeAST's node that conflict
+		// Rename any symbols defined within rewritePkgRefs's node that conflict
 		// with any symbols in the generated file.
 		objName := obj.Name()
 		if pos := obj.Pos(); pos < start || end <= pos || !(g.nameInFileScope(objName) || inNewNames(objName)) {
@@ -530,7 +347,14 @@ func (g *gen) writeAST(fset *token.FileSet, info *types.Info, node ast.Node) {
 		}
 		return true
 	})
-	if err := printer.Fprint(&g.buf, fset, node); err != nil {
+	return node
+}
+
+// writeAST prints an AST node into the generated output, rewriting any
+// package references it encounters.
+func (g *gen) writeAST(info *types.Info, node ast.Node) {
+	node = g.rewritePkgRefs(info, node)
+	if err := printer.Fprint(&g.buf, g.prog.Fset, node); err != nil {
 		panic(err)
 	}
 }
@@ -583,6 +407,196 @@ func (g *gen) p(format string, args ...interface{}) {
 	fmt.Fprintf(&g.buf, format, args...)
 }
 
+// injectorGen is the per-injector pass generator state.
+type injectorGen struct {
+	g *gen
+
+	paramNames   []string
+	localNames   []string
+	cleanupNames []string
+	errVar       string
+
+	// discard causes ig.p and ig.writeAST to no-op. Useful to run
+	// generation for side-effects like filling in g.imports.
+	discard bool
+}
+
+// injectPass generates an injector given the output from analysis.
+func injectPass(name string, params *types.Tuple, injectSig outputSignature, calls []call, ig *injectorGen) {
+	ig.p("func %s(", name)
+	for i := 0; i < params.Len(); i++ {
+		if i > 0 {
+			ig.p(", ")
+		}
+		pi := params.At(i)
+		a := pi.Name()
+		if a == "" || a == "_" {
+			a = typeVariableName(pi.Type())
+			if a == "" {
+				a = "arg"
+			}
+		}
+		ig.paramNames = append(ig.paramNames, disambiguate(a, ig.nameInInjector))
+		ig.p("%s %s", ig.paramNames[i], types.TypeString(pi.Type(), ig.g.qualifyPkg))
+	}
+	outTypeString := types.TypeString(injectSig.out, ig.g.qualifyPkg)
+	if injectSig.cleanup && injectSig.err {
+		ig.p(") (%s, func(), error) {\n", outTypeString)
+	} else if injectSig.cleanup {
+		ig.p(") (%s, func()) {\n", outTypeString)
+	} else if injectSig.err {
+		ig.p(") (%s, error) {\n", outTypeString)
+	} else {
+		ig.p(") %s {\n", outTypeString)
+	}
+	for i := range calls {
+		c := &calls[i]
+		lname := typeVariableName(c.out)
+		if lname == "" {
+			lname = "v"
+		}
+		lname = disambiguate(lname, ig.nameInInjector)
+		ig.localNames = append(ig.localNames, lname)
+		switch c.kind {
+		case structProvider:
+			ig.structProviderCall(lname, c)
+		case funcProviderCall:
+			ig.funcProviderCall(lname, c, injectSig)
+		case valueExpr:
+			ig.valueExpr(lname, c)
+		default:
+			panic("unknown kind")
+		}
+	}
+	if len(calls) == 0 {
+		for i := 0; i < params.Len(); i++ {
+			if types.Identical(injectSig.out, params.At(i).Type()) {
+				ig.p("\treturn %s", ig.paramNames[i])
+				break
+			}
+		}
+	} else {
+		ig.p("\treturn %s", ig.localNames[len(calls)-1])
+	}
+	if injectSig.cleanup {
+		ig.p(", func() {\n")
+		for i := len(ig.cleanupNames) - 1; i >= 0; i-- {
+			ig.p("\t\t%s()\n", ig.cleanupNames[i])
+		}
+		ig.p("\t}")
+	}
+	if injectSig.err {
+		ig.p(", nil")
+	}
+	ig.p("\n}\n\n")
+}
+
+func (ig *injectorGen) funcProviderCall(lname string, c *call, injectSig outputSignature) {
+	ig.p("\t%s", lname)
+	prevCleanup := len(ig.cleanupNames)
+	if c.hasCleanup {
+		cname := disambiguate("cleanup", ig.nameInInjector)
+		ig.cleanupNames = append(ig.cleanupNames, cname)
+		ig.p(", %s", cname)
+	}
+	if c.hasErr {
+		ig.p(", %s", ig.errVar)
+	}
+	ig.p(" := ")
+	ig.p("%s(", ig.g.qualifiedID(c.importPath, c.name))
+	for i, a := range c.args {
+		if i > 0 {
+			ig.p(", ")
+		}
+		if a < len(ig.paramNames) {
+			ig.p("%s", ig.paramNames[a])
+		} else {
+			ig.p("%s", ig.localNames[a-len(ig.paramNames)])
+		}
+	}
+	ig.p(")\n")
+	if c.hasErr {
+		ig.p("\tif %s != nil {\n", ig.errVar)
+		for i := prevCleanup - 1; i >= 0; i-- {
+			ig.p("\t\t%s()\n", ig.cleanupNames[i])
+		}
+		ig.p("\t\treturn %s", zeroValue(injectSig.out, ig.g.qualifyPkg))
+		if injectSig.cleanup {
+			ig.p(", nil")
+		}
+		// TODO(light): Give information about failing provider.
+		ig.p(", err\n")
+		ig.p("\t}\n")
+	}
+}
+
+func (ig *injectorGen) structProviderCall(lname string, c *call) {
+	ig.p("\t%s", lname)
+	ig.p(" := ")
+	if _, ok := c.out.(*types.Pointer); ok {
+		ig.p("&")
+	}
+	ig.p("%s{\n", ig.g.qualifiedID(c.importPath, c.name))
+	for i, a := range c.args {
+		ig.p("\t\t%s: ", c.fieldNames[i])
+		if a < len(ig.paramNames) {
+			ig.p("%s", ig.paramNames[a])
+		} else {
+			ig.p("%s", ig.localNames[a-len(ig.paramNames)])
+		}
+		ig.p(",\n")
+	}
+	ig.p("\t}\n")
+}
+
+func (ig *injectorGen) valueExpr(lname string, c *call) {
+	ig.p("\t%s", lname)
+	ig.p(" := ")
+	ig.writeAST(c.valueTypeInfo, c.valueExpr)
+	ig.p("\n")
+}
+
+// nameInInjector reports whether name collides with any other identifier
+// in the current injector.
+func (ig *injectorGen) nameInInjector(name string) bool {
+	if name == ig.errVar {
+		return true
+	}
+	for _, a := range ig.paramNames {
+		if a == name {
+			return true
+		}
+	}
+	for _, l := range ig.localNames {
+		if l == name {
+			return true
+		}
+	}
+	for _, l := range ig.cleanupNames {
+		if l == name {
+			return true
+		}
+	}
+	return ig.g.nameInFileScope(name)
+}
+
+func (ig *injectorGen) p(format string, args ...interface{}) {
+	if ig.discard {
+		return
+	}
+	ig.g.p(format, args...)
+}
+
+func (ig *injectorGen) writeAST(info *types.Info, node ast.Node) {
+	node = ig.g.rewritePkgRefs(info, node)
+	if ig.discard {
+		return
+	}
+	if err := printer.Fprint(&ig.g.buf, ig.g.prog.Fset, node); err != nil {
+		panic(err)
+	}
+}
+
 // zeroValue returns the shortest expression that evaluates to the zero
 // value for the given type.
 func zeroValue(t types.Type, qf types.Qualifier) string {

internal/goose/parse.go

@@ -15,6 +15,7 @@
 package goose
 
 import (
+	"errors"
 	"fmt"
 	"go/ast"
 	"go/build"
@@ -384,43 +385,20 @@ func qualifiedIdentObject(info *types.Info, expr ast.Expr) types.Object {
 // processFuncProvider creates a provider for a function declaration.
 func processFuncProvider(fset *token.FileSet, fn *types.Func) (*Provider, error) {
 	sig := fn.Type().(*types.Signature)
-
 	fpos := fn.Pos()
-	r := sig.Results()
-	var hasCleanup, hasErr bool
-	switch r.Len() {
-	case 1:
-		hasCleanup, hasErr = false, false
-	case 2:
-		switch t := r.At(1).Type(); {
-		case types.Identical(t, errorType):
-			hasCleanup, hasErr = false, true
-		case types.Identical(t, cleanupType):
-			hasCleanup, hasErr = true, false
-		default:
-			return nil, fmt.Errorf("%v: wrong signature for provider %s: second return type must be error or func()", fset.Position(fpos), fn.Name())
+	providerSig, err := funcOutput(sig)
+	if err != nil {
+		return nil, fmt.Errorf("%v: wrong signature for provider %s: %v", fset.Position(fpos), fn.Name(), err)
 	}
-	case 3:
-		if t := r.At(1).Type(); !types.Identical(t, cleanupType) {
-			return nil, fmt.Errorf("%v: wrong signature for provider %s: second return type must be func()", fset.Position(fpos), fn.Name())
-		}
-		if t := r.At(2).Type(); !types.Identical(t, errorType) {
-			return nil, fmt.Errorf("%v: wrong signature for provider %s: third return type must be error", fset.Position(fpos), fn.Name())
-		}
-		hasCleanup, hasErr = true, true
-	default:
-		return nil, fmt.Errorf("%v: wrong signature for provider %s: must have one return value and optional error", fset.Position(fpos), fn.Name())
-	}
-	out := r.At(0).Type()
 	params := sig.Params()
 	provider := &Provider{
 		ImportPath: fn.Pkg().Path(),
 		Name:       fn.Name(),
 		Pos:        fn.Pos(),
 		Args:       make([]ProviderInput, params.Len()),
-		Out:        out,
-		HasCleanup: hasCleanup,
-		HasErr:     hasErr,
+		Out:        providerSig.out,
+		HasCleanup: providerSig.cleanup,
+		HasErr:     providerSig.err,
 	}
 	for i := 0; i < params.Len(); i++ {
 		provider.Args[i] = ProviderInput{
@@ -435,6 +413,47 @@ func processFuncProvider(fset *token.FileSet, fn *types.Func) (*Provider, error)
 	return provider, nil
 }
 
+type outputSignature struct {
+	out     types.Type
+	cleanup bool
+	err     bool
+}
+
+// funcOutput validates an injector or provider function's return signature.
+func funcOutput(sig *types.Signature) (outputSignature, error) {
+	results := sig.Results()
+	switch results.Len() {
+	case 0:
+		return outputSignature{}, errors.New("no return values")
+	case 1:
+		return outputSignature{out: results.At(0).Type()}, nil
+	case 2:
+		out := results.At(0).Type()
+		switch t := results.At(1).Type(); {
+		case types.Identical(t, errorType):
+			return outputSignature{out: out, err: true}, nil
+		case types.Identical(t, cleanupType):
+			return outputSignature{out: out, cleanup: true}, nil
+		default:
+			return outputSignature{}, fmt.Errorf("second return type is %s; must be error or func()", types.TypeString(t, nil))
+		}
+	case 3:
+		if t := results.At(1).Type(); !types.Identical(t, cleanupType) {
+			return outputSignature{}, fmt.Errorf("second return type is %s; must be func()", types.TypeString(t, nil))
+		}
+		if t := results.At(2).Type(); !types.Identical(t, errorType) {
+			return outputSignature{}, fmt.Errorf("third return type is %s; must be error", types.TypeString(t, nil))
+		}
+		return outputSignature{
+			out:     results.At(0).Type(),
+			cleanup: true,
+			err:     true,
+		}, nil
+	default:
+		return outputSignature{}, errors.New("too many return values")
+	}
+}
+
 // processStructProvider creates a provider for a named struct type.
 // It only produces the non-pointer variant.
 func processStructProvider(fset *token.FileSet, typeName *types.TypeName) (*Provider, error) {