simplify anonymous import handling

Anonymous imports were being special-cased and written out separately. They're not that special though, we can just count them as regular imports with the name "_".

This causes them to get grouped together with the other imports like one would expect, and simplifies the generator a bit.

Fixes google#358.

internal/wire/wire.go

@@ -188,7 +188,10 @@ func generateInjectors(g *gen, pkg *packages.Package) (injectorFiles []*ast.File
 
 		for _, impt := range f.Imports {
 			if impt.Name != nil && impt.Name.Name == "_" {
-				g.anonImports[impt.Path.Value] = true
+				g.imports[strings.Trim(impt.Path.Value, `"`)] = importInfo{
+					name:    "_",
+					differs: true,
+				}
 			}
 		}
 	}
@@ -241,19 +244,17 @@ type importInfo struct {
 
 // gen is the file-wide generator state.
 type gen struct {
-	pkg         *packages.Package
-	buf         bytes.Buffer
-	imports     map[string]importInfo
-	anonImports map[string]bool
-	values      map[ast.Expr]string
+	pkg     *packages.Package
+	buf     bytes.Buffer
+	imports map[string]importInfo
+	values  map[ast.Expr]string
 }
 
 func newGen(pkg *packages.Package) *gen {
 	return &gen{
-		pkg:         pkg,
-		anonImports: make(map[string]bool),
-		imports:     make(map[string]importInfo),
-		values:      make(map[ast.Expr]string),
+		pkg:     pkg,
+		imports: make(map[string]importInfo),
+		values:  make(map[ast.Expr]string),
 	}
 }
 
@@ -290,19 +291,6 @@ func (g *gen) frame(tags string) []byte {
 		}
 		buf.WriteString(")\n\n")
 	}
-	if len(g.anonImports) > 0 {
-		buf.WriteString("import (\n")
-		anonImps := make([]string, 0, len(g.anonImports))
-		for path := range g.anonImports {
-			anonImps = append(anonImps, path)
-		}
-		sort.Strings(anonImps)
-
-		for _, path := range anonImps {
-			fmt.Fprintf(&buf, "\t_ %s\n", path)
-		}
-		buf.WriteString(")\n\n")
-	}
 	buf.Write(g.buf.Bytes())
 	return buf.Bytes()
 }