implement linter

Author: jirfag

README.md

@@ -1 +1,16 @@
 # go-printf-func-name
+
+The Go linter `go-printf-func-name` checks that printf-like functions are named with `f` at the end.
+
+For example, `myLog` should be named `myLogf` by Go convention:
+
+```go
+package main
+
+import "log"
+
+func myLog(format string, args ...interface{}) {
+	const prefix = "[my] "
+	log.Printf(prefix + format, args...)
+}
+```

cmd/go-printf-func-name/main.go

@@ -0,0 +1,10 @@
+package main
+
+import (
+	"github.com/jirfag/go-printf-func-name/pkg/analyzer"
+	"golang.org/x/tools/go/analysis/singlechecker"
+)
+
+func main() {
+	singlechecker.Main(analyzer.Analyzer)
+}

go.mod

@@ -0,0 +1,5 @@
+module github.com/jirfag/go-printf-func-name
+
+go 1.13
+
+require golang.org/x/tools v0.0.0-20191108193012-7d206e10da11

go.sum

@@ -0,0 +1,9 @@
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20191108193012-7d206e10da11 h1:Yq9t9jnGoR+dBuitxdo9l6Q7xh/zOyNnYUtDKaQ3x0E=
+golang.org/x/tools v0.0.0-20191108193012-7d206e10da11/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/tools v0.0.0-20191109212701-97ad0ed33101 h1:LCmXVkvpQCDj724eX6irUTPCJP5GelFHxqGSWL2D1R0=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

pkg/analyzer/analyzer.go

@@ -0,0 +1,66 @@
+package analyzer
+
+import (
+	"go/ast"
+	"strings"
+
+	"golang.org/x/tools/go/analysis/passes/inspect"
+	"golang.org/x/tools/go/ast/inspector"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+var Analyzer = &analysis.Analyzer{
+	Name:     "go_printf_func_name",
+	Doc:      "Checks that printf-like functions are named with `f` at the end.",
+	Run:      run,
+	Requires: []*analysis.Analyzer{inspect.Analyzer},
+}
+
+func run(pass *analysis.Pass) (interface{}, error) {
+	inspector := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
+	nodeFilter := []ast.Node{
+		(*ast.FuncDecl)(nil),
+	}
+
+	inspector.Preorder(nodeFilter, func(node ast.Node) {
+		funcDecl := node.(*ast.FuncDecl)
+
+		params := funcDecl.Type.Params.List
+		if len(params) < 2 { // [0] must be format (string), [1] must be args (...interface{})
+			return
+		}
+
+		formatParamType, ok := params[len(params)-2].Type.(*ast.Ident)
+		if !ok { // first param type isn't identificator so it can't be of type "string"
+			return
+		}
+
+		if formatParamType.Name != "string" { // first param (format) type is not string
+			return
+		}
+
+		argsParamType, ok := params[len(params)-1].Type.(*ast.Ellipsis)
+		if !ok { // args are not ellipsis (...args)
+			return
+		}
+
+		elementType, ok := argsParamType.Elt.(*ast.InterfaceType)
+		if !ok { // args are not of interface type, but we need interface{}
+			return
+		}
+
+		if elementType.Methods != nil && len(elementType.Methods.List) != 0 {
+			return // has >= 1 method in interface, but we need an empty interface "interface{}"
+		}
+
+		if strings.HasSuffix(funcDecl.Name.Name, "f") {
+			return
+		}
+
+		pass.Reportf(node.Pos(), "printf-like formatting function '%s' should be named '%sf'\n",
+			funcDecl.Name.Name, funcDecl.Name.Name)
+	})
+
+	return nil, nil
+}

pkg/analyzer/analyzer_test.go

@@ -0,0 +1,20 @@
+package analyzer_test
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/jirfag/go-printf-func-name/pkg/analyzer"
+	"golang.org/x/tools/go/analysis/analysistest"
+)
+
+func TestAll(t *testing.T) {
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("Failed to get wd: %s", err)
+	}
+
+	testdata := filepath.Join(filepath.Dir(filepath.Dir(wd)), "testdata")
+	analysistest.Run(t, testdata, analyzer.Analyzer, "p")
+}

testdata/src/p/p.go

@@ -0,0 +1,28 @@
+package p
+
+func notPrintfFuncAtAll() {}
+
+func funcWithEllipsis(args ...interface{}) {}
+
+func printfLikeButWithStrings(format string, args ...string) {}
+
+func printfLikeButWithBadFormat(format int, args ...interface{}) {}
+
+func secondArgIsNotEllipsis(arg1 string, arg2 int) {}
+
+func printfLikeButWithExtraInterfaceMethods(format string, args ...interface {
+	String() string
+}) {
+}
+
+func prinfLikeFuncf(format string, args ...interface{}) {}
+
+func prinfLikeFunc(format string, args ...interface{}) {} // want "printf-like formatting function"
+
+func prinfLikeFuncWithExtraArgs1(extraArg, format string, args ...interface{}) {} // want "printf-like formatting function"
+
+func prinfLikeFuncWithExtraArgs2(extraArg int, format string, args ...interface{}) {} // want "printf-like formatting function"
+
+func prinfLikeFuncWithReturnValue(format string, args ...interface{}) string { // want "printf-like formatting function"
+	return ""
+}