Add staticcheck tool

vendor/honnef.co/go/tools/staticcheck/sa9004/sa9004.go

@@ -0,0 +1,185 @@
+package sa9004
+
+import (
+	"go/ast"
+	"go/token"
+	"go/types"
+
+	"honnef.co/go/tools/analysis/code"
+	"honnef.co/go/tools/analysis/edit"
+	"honnef.co/go/tools/analysis/lint"
+	"honnef.co/go/tools/analysis/report"
+	"honnef.co/go/tools/go/ast/astutil"
+
+	"golang.org/x/tools/go/analysis"
+	"golang.org/x/tools/go/analysis/passes/inspect"
+)
+
+var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
+	Analyzer: &analysis.Analyzer{
+		Name:     "SA9004",
+		Run:      run,
+		Requires: []*analysis.Analyzer{inspect.Analyzer},
+	},
+	Doc: &lint.RawDocumentation{
+		Title: `Only the first constant has an explicit type`,
+
+		Text: `In a constant declaration such as the following:
+
+    const (
+        First byte = 1
+        Second     = 2
+    )
+
+the constant Second does not have the same type as the constant First.
+This construct shouldn't be confused with
+
+    const (
+        First byte = iota
+        Second
+    )
+
+where \'First\' and \'Second\' do indeed have the same type. The type is only
+passed on when no explicit value is assigned to the constant.
+
+When declaring enumerations with explicit values it is therefore
+important not to write
+
+    const (
+          EnumFirst EnumType = 1
+          EnumSecond         = 2
+          EnumThird          = 3
+    )
+
+This discrepancy in types can cause various confusing behaviors and
+bugs.
+
+
+Wrong type in variable declarations
+
+The most obvious issue with such incorrect enumerations expresses
+itself as a compile error:
+
+    package pkg
+
+    const (
+        EnumFirst  uint8 = 1
+        EnumSecond       = 2
+    )
+
+    func fn(useFirst bool) {
+        x := EnumSecond
+        if useFirst {
+            x = EnumFirst
+        }
+    }
+
+fails to compile with
+
+    ./const.go:11:5: cannot use EnumFirst (type uint8) as type int in assignment
+
+
+Losing method sets
+
+A more subtle issue occurs with types that have methods and optional
+interfaces. Consider the following:
+
+    package main
+
+    import "fmt"
+
+    type Enum int
+
+    func (e Enum) String() string {
+        return "an enum"
+    }
+
+    const (
+        EnumFirst  Enum = 1
+        EnumSecond      = 2
+    )
+
+    func main() {
+        fmt.Println(EnumFirst)
+        fmt.Println(EnumSecond)
+    }
+
+This code will output
+
+    an enum
+    2
+
+as \'EnumSecond\' has no explicit type, and thus defaults to \'int\'.`,
+		Since:    "2019.1",
+		Severity: lint.SeverityWarning,
+		MergeIf:  lint.MergeIfAny,
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+
+func run(pass *analysis.Pass) (any, error) {
+	fn := func(node ast.Node) {
+		decl := node.(*ast.GenDecl)
+		if !decl.Lparen.IsValid() {
+			return
+		}
+		if decl.Tok != token.CONST {
+			return
+		}
+
+		groups := astutil.GroupSpecs(pass.Fset, decl.Specs)
+	groupLoop:
+		for _, group := range groups {
+			if len(group) < 2 {
+				continue
+			}
+			if group[0].(*ast.ValueSpec).Type == nil {
+				// first constant doesn't have a type
+				continue groupLoop
+			}
+
+			firstType := pass.TypesInfo.TypeOf(group[0].(*ast.ValueSpec).Values[0])
+			for i, spec := range group {
+				spec := spec.(*ast.ValueSpec)
+				if i > 0 && spec.Type != nil {
+					continue groupLoop
+				}
+				if len(spec.Names) != 1 || len(spec.Values) != 1 {
+					continue groupLoop
+				}
+
+				if !types.ConvertibleTo(pass.TypesInfo.TypeOf(spec.Values[0]), firstType) {
+					continue groupLoop
+				}
+
+				switch v := spec.Values[0].(type) {
+				case *ast.BasicLit:
+				case *ast.UnaryExpr:
+					if _, ok := v.X.(*ast.BasicLit); !ok {
+						continue groupLoop
+					}
+				default:
+					// if it's not a literal it might be typed, such as
+					// time.Microsecond = 1000 * Nanosecond
+					continue groupLoop
+				}
+			}
+			var edits []analysis.TextEdit
+			typ := group[0].(*ast.ValueSpec).Type
+			for _, spec := range group[1:] {
+				nspec := *spec.(*ast.ValueSpec)
+				nspec.Type = typ
+				// The position of `spec` node excludes comments (if any).
+				// However, on generating the source back from the node, the comments are included. Setting `Comment` to nil ensures deduplication of comments.
+				nspec.Comment = nil
+				edits = append(edits, edit.ReplaceWithNode(pass.Fset, spec, &nspec))
+			}
+			report.Report(pass, group[0],
+				"only the first constant in this group has an explicit type",
+				report.Fixes(edit.Fix("Add type to all constants in group", edits...)))
+		}
+	}
+	code.Preorder(pass, fn, (*ast.GenDecl)(nil))
+	return nil, nil
+}