go/src/cmd/compile/internal/syntax/branches.go

// checkBranches checks correct use of labels and branch
// statements (break, continue, fallthrough, goto) in a function body.
// It catches:
//   - misplaced breaks, continues, and fallthroughs
//   - bad labeled breaks and continues
//   - invalid, unused, duplicate, and missing labels
//   - gotos jumping over variable declarations and into blocks
func checkBranches(body *BlockStmt, errh ErrorHandler) { … }

type labelScope …

type label …

type block …

func (ls *labelScope) errf(pos Pos, format string, args ...interface{ … }

// declare declares the label introduced by s in block b and returns
// the new label. If the label was already declared, declare reports
// and error and the existing label is returned instead.
func (ls *labelScope) declare(b *block, s *LabeledStmt) *label { … }

// gotoTarget returns the labeled statement matching the given name and
// declared in block b or any of its enclosing blocks. The result is nil
// if the label is not defined, or doesn't match a valid labeled statement.
func (ls *labelScope) gotoTarget(b *block, name string) *LabeledStmt { … }

var invalid …

// enclosingTarget returns the innermost enclosing labeled statement matching
// the given name. The result is nil if the label is not defined, and invalid
// if the label is defined but doesn't label a valid labeled statement.
func (ls *labelScope) enclosingTarget(b *block, name string) *LabeledStmt { … }

type targets …

// blockBranches processes a block's body starting at start and returns the
// list of unresolved (forward) gotos. parent is the immediately enclosing
// block (or nil), ctxt provides information about the enclosing statements,
// and lstmt is the labeled statement associated with this block, or nil.
func (ls *labelScope) blockBranches(parent *block, ctxt targets, lstmt *LabeledStmt, start Pos, body []Stmt) []*BranchStmt { … }

func trimTrailingEmptyStmts(list []Stmt) []Stmt { … }