1 package st1015
2 3 import (
4 "go/ast"
5 "go/token"
6 7 "honnef.co/go/tools/analysis/code"
8 "honnef.co/go/tools/analysis/facts/generated"
9 "honnef.co/go/tools/analysis/lint"
10 "honnef.co/go/tools/analysis/report"
11 12 "golang.org/x/tools/go/analysis"
13 "golang.org/x/tools/go/analysis/passes/inspect"
14 )
15 16 var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
17 Analyzer: &analysis.Analyzer{
18 Name: "ST1015",
19 Run: run,
20 Requires: []*analysis.Analyzer{inspect.Analyzer, generated.Analyzer},
21 },
22 Doc: &lint.RawDocumentation{
23 Title: `A switch's default case should be the first or last case`,
24 Since: "2019.1",
25 MergeIf: lint.MergeIfAny,
26 },
27 })
28 29 var Analyzer = SCAnalyzer.Analyzer
30 31 func run(pass *analysis.Pass) (interface{}, error) {
32 hasFallthrough := func(clause ast.Stmt) bool {
33 // A valid fallthrough statement may be used only as the final non-empty statement in a case clause. Thus we can
34 // easily avoid falsely matching fallthroughs in nested switches by not descending into blocks.
35 36 body := clause.(*ast.CaseClause).Body
37 for i := len(body) - 1; i >= 0; i-- {
38 last := body[i]
39 switch stmt := last.(type) {
40 case *ast.EmptyStmt:
41 // Fallthrough may be followed by empty statements
42 case *ast.BranchStmt:
43 return stmt.Tok == token.FALLTHROUGH
44 default:
45 return false
46 }
47 }
48 49 return false
50 }
51 52 fn := func(node ast.Node) {
53 stmt := node.(*ast.SwitchStmt)
54 list := stmt.Body.List
55 defaultIdx := -1
56 for i, c := range list {
57 if c.(*ast.CaseClause).List == nil {
58 defaultIdx = i
59 break
60 }
61 }
62 63 if defaultIdx == -1 || defaultIdx == 0 || defaultIdx == len(list)-1 {
64 // No default case, or it's the first or last case
65 return
66 }
67 68 if hasFallthrough(list[defaultIdx-1]) || hasFallthrough(list[defaultIdx]) {
69 // We either fall into or out of this case; don't mess with the order
70 return
71 }
72 73 report.Report(pass, list[defaultIdx], "default case should be first or last in switch statement", report.FilterGenerated())
74 }
75 code.Preorder(pass, fn, (*ast.SwitchStmt)(nil))
76 return nil, nil
77 }
78