wire: add info from the dependency graph when a type is not provided

internal/wire/analyze.go

@@ -122,6 +122,7 @@ func solve(fset *token.FileSet, out types.Type, given []types.Type, set *Provide
 	type frame struct {
 		t    types.Type
 		from types.Type
+		up   *frame
 	}
 	stk := []frame{{t: out}}
 dfs:
@@ -135,12 +136,15 @@ dfs:
 		switch pv := set.For(curr.t); {
 		case pv.IsNil():
 			if curr.from == nil {
-				ec.add(fmt.Errorf("no provider found for %s (output of injector)", types.TypeString(curr.t, nil)))
+				ec.add(fmt.Errorf("no provider found for %s, output of injector", types.TypeString(curr.t, nil)))
 				index.Set(curr.t, errAbort)
 				continue
 			}
-			// TODO(light): Give name of provider.
-			ec.add(fmt.Errorf("no provider found for %s (required by provider of %s)", types.TypeString(curr.t, nil), types.TypeString(curr.from, nil)))
+			neededBy := []string{types.TypeString(curr.t, nil)}
+			for f := curr.up; f != nil; f = f.up {
+				neededBy = append(neededBy, fmt.Sprintf("%s in %s", types.TypeString(f.t, nil), set.srcMap.At(f.t).(*providerSetSrc).description(fset, f.t)))
+			}
+			ec.add(fmt.Errorf("no provider found for %s", strings.Join(neededBy, ", needed by ")))
 			index.Set(curr.t, errAbort)
 			continue
 		case pv.IsProvider():
@@ -151,7 +155,7 @@ dfs:
 				// Interface binding.  Don't create a call ourselves.
 				i := index.At(concrete)
 				if i == nil {
-					stk = append(stk, curr, frame{t: concrete, from: curr.t})
+					stk = append(stk, curr, frame{t: concrete, from: curr.t, up: &curr})
 					continue
 				}
 				index.Set(curr.t, i)
@@ -169,7 +173,7 @@ dfs:
 						stk = append(stk, curr)
 						visitedArgs = false
 					}
-					stk = append(stk, frame{t: a.Type, from: curr.t})
+					stk = append(stk, frame{t: a.Type, from: curr.t, up: &curr})
 				}
 			}
 			if !visitedArgs {
@@ -208,7 +212,7 @@ dfs:
 				// Interface binding.  Don't create a call ourselves.
 				i := index.At(v.Out)
 				if i == nil {
-					stk = append(stk, curr, frame{t: v.Out, from: curr.t})
+					stk = append(stk, curr, frame{t: v.Out, from: curr.t, up: &curr})
 					continue
 				}
 				index.Set(curr.t, i)

internal/wire/parse.go

@@ -38,34 +38,42 @@ type providerSetSrc struct {
 	Import   *ProviderSet
 }
 
-// trace returns a slice of strings describing the (possibly recursive) source
-// of p, including line numbers.
-func (p *providerSetSrc) trace(fset *token.FileSet, typ types.Type) []string {
+// description returns a string describing the source of p, including line numbers.
+func (p *providerSetSrc) description(fset *token.FileSet, typ types.Type) string {
 	quoted := func(s string) string {
 		if s == "" {
 			return ""
 		}
 		return fmt.Sprintf("%q ", s)
 	}
-	var retval []string
-	if p.Provider != nil {
+	switch {
+	case p.Provider != nil:
 		kind := "provider"
 		if p.Provider.IsStruct {
 			kind = "struct provider"
 		}
-		retval = append(retval, fmt.Sprintf("%s %s(%s)", kind, quoted(p.Provider.Name), fset.Position(p.Provider.Pos)))
-	} else if p.Binding != nil {
-		retval = append(retval, fmt.Sprintf("wire.Bind (%s)", fset.Position(p.Binding.Pos)))
-	} else if p.Value != nil {
-		retval = append(retval, fmt.Sprintf("wire.Value (%s)", fset.Position(p.Value.Pos)))
-	} else if p.Import != nil {
+		return fmt.Sprintf("%s %s(%s)", kind, quoted(p.Provider.Name), fset.Position(p.Provider.Pos))
+	case p.Binding != nil:
+		return fmt.Sprintf("wire.Bind (%s)", fset.Position(p.Binding.Pos))
+	case p.Value != nil:
+		return fmt.Sprintf("wire.Value (%s)", fset.Position(p.Value.Pos))
+	case p.Import != nil:
+		return fmt.Sprintf("provider set %s(%s)", quoted(p.Import.VarName), fset.Position(p.Import.Pos))
+	}
+	panic("providerSetSrc with no fields set")
+}
+
+// trace returns a slice of strings describing the (possibly recursive) source
+// of p, including line numbers.
+func (p *providerSetSrc) trace(fset *token.FileSet, typ types.Type) []string {
+	var retval []string
+	// Only Imports need recursion.
+	if p.Import != nil {
 		if parent := p.Import.srcMap.At(typ); parent != nil {
 			retval = append(retval, parent.(*providerSetSrc).trace(fset, typ)...)
 		}
-		retval = append(retval, fmt.Sprintf("provider set %s(%s)", quoted(p.Import.VarName), fset.Position(p.Import.Pos)))
-	} else {
-		panic("providerSetSrc with no fields set")
 	}
+	retval = append(retval, p.description(fset, typ))
 	return retval
 }
 

internal/wire/testdata/MultipleMissingInputs/foo/foo.go

@@ -17,7 +17,9 @@ package main
 import "fmt"
 
 func main() {
-	fmt.Println(injectBaz())
+	fmt.Println(injectMissingOutputType())
+	fmt.Println(injectMultipleMissingTypes())
+	fmt.Println(injectMissingRecursiveType())
 }
 
 type Foo int
@@ -27,3 +29,19 @@ type Baz int
 func provideBaz(foo Foo, bar Bar) Baz {
 	return 0
 }
+
+type Zip int
+type Zap int
+type Zop int
+
+func provideZip(foo Foo) Zip {
+	return 0
+}
+
+func provideZap(zip Zip) Zap {
+	return 0
+}
+
+func provideZop(zap Zap) Zop {
+	return 0
+}

internal/wire/testdata/MultipleMissingInputs/foo/wire.go

@@ -20,7 +20,23 @@ import (
 	"github.com/google/go-cloud/wire"
 )
 
-func injectBaz() Baz {
+func injectMissingOutputType() Foo {
+	// Error: no provider for Foo.
+	wire.Build()
+	return Foo(0)
+}
+
+func injectMultipleMissingTypes() Baz {
+	// Error: provideBaz needs Foo and Bar, both missing.
 	wire.Build(provideBaz)
 	return Baz(0)
 }
+
+func injectMissingRecursiveType() Zop {
+	// Error:
+	// Zop  -> Zap -> Zip -> Foo
+	// provideZop needs Zap, provideZap needs Zip, provideZip needs Foo,
+	// which is missing.
+	wire.Build(provideZop, provideZap, provideZip)
+	return Zop(0)
+}

internal/wire/testdata/MultipleMissingInputs/want/wire_errs.txt

@@ -1,2 +1,4 @@
-no provider found for example.com/foo.Foo
-no provider found for example.com/foo.Bar
+inject injectMissingOutputType: no provider found for example.com/foo.Foo, output of injector
+inject injectMultipleMissingTypes: no provider found for example.com/foo.Foo, needed by example.com/foo.Baz in provider "provideBaz" (/wire_gopath/src/example.com/foo/foo.go:29:6)
+inject injectMultipleMissingTypes: no provider found for example.com/foo.Bar, needed by example.com/foo.Baz in provider "provideBaz" (/wire_gopath/src/example.com/foo/foo.go:29:6)
+inject injectMissingRecursiveType: no provider found for example.com/foo.Foo, needed by example.com/foo.Zip in provider "provideZip" (/wire_gopath/src/example.com/foo/foo.go:37:6), needed by example.com/foo.Zap in provider "provideZap" (/wire_gopath/src/example.com/foo/foo.go:41:6), needed by example.com/foo.Zop in provider "provideZop" (/wire_gopath/src/example.com/foo/foo.go:45:6)