github.com/amarpal/go-tools@v0.0.0-20240422043104-40142f59f616/stylecheck/st1015/st1015.go (about)

     1  package st1015
     2  
     3  import (
     4  	"go/ast"
     5  	"go/token"
     6  
     7  	"github.com/amarpal/go-tools/analysis/code"
     8  	"github.com/amarpal/go-tools/analysis/facts/generated"
     9  	"github.com/amarpal/go-tools/analysis/lint"
    10  	"github.com/amarpal/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.Documentation{
    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  }