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block_scanner.go
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block_scanner.go
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package main
import (
"bytes"
"go/ast"
"go/token"
)
type Block struct {
startByte token.Pos
endByte token.Pos
numStmt int
}
type ScanFn func(startLine, endLine, blockNum int) (insert string)
type BlockScanner struct {
fset *token.FileSet
edit *Buffer
content []byte
scanner ScanFn
blockNum int
}
func NewBlockScanner(fset *token.FileSet, src []byte, scanner ScanFn) *BlockScanner {
return &BlockScanner{
fset: fset,
content: src,
edit: NewBuffer(src),
scanner: scanner,
}
}
func (b *BlockScanner) Res() []byte {
return b.edit.Bytes()
}
func (b *BlockScanner) Visit(node ast.Node) ast.Visitor {
/* if b != nil {
fmt.Println("===================")
fmt.Printf("%T\n", node)
}*/
switch n := node.(type) {
case *ast.BlockStmt:
// If it's a switch or select, the body is a list of case clauses; don't tag the block itself.
if len(n.List) > 0 {
switch n.List[0].(type) {
case *ast.CaseClause: // switch
for _, n := range n.List {
clause := n.(*ast.CaseClause)
b.addCounters(clause.Colon+1, clause.Colon+1, clause.End(), clause.Body, false)
}
return b
case *ast.CommClause: // select
for _, n := range n.List {
clause := n.(*ast.CommClause)
b.addCounters(clause.Colon+1, clause.Colon+1, clause.End(), clause.Body, false)
}
return b
}
}
b.addCounters(n.Lbrace, n.Lbrace+1, n.Rbrace+1, n.List, true) // +1 to step past closing brace.
case *ast.IfStmt:
if n.Init != nil {
ast.Walk(b, n.Init)
}
ast.Walk(b, n.Cond)
ast.Walk(b, n.Body)
if n.Else == nil {
return nil
}
// The elses are special, because if we have
// if x {
// } else if y {
// }
// we want to cover the "if y". To do this, we need a place to drop the counter,
// so we add a hidden block:
// if x {
// } else {
// if y {
// }
// }
elseOffset := b.findText(n.Body.End(), "else")
if elseOffset < 0 {
panic("lost else")
}
b.edit.Insert(elseOffset+4, "{")
b.edit.Insert(b.offset(n.Else.End()), "}")
// We just created a block, now walk it.
// Adjust the position of the new block to start after
// the "else". That will cause it to follow the "{"
// we inserted above.
pos := b.fset.File(n.Body.End()).Pos(elseOffset + 4)
switch stmt := n.Else.(type) {
case *ast.IfStmt:
block := &ast.BlockStmt{
Lbrace: pos,
List: []ast.Stmt{stmt},
Rbrace: stmt.End(),
}
n.Else = block
case *ast.BlockStmt:
stmt.Lbrace = pos
default:
panic("unexpected node type in if")
}
ast.Walk(b, n.Else)
return nil
case *ast.SelectStmt:
// Don't annotate an empty select - creates a syntax error.
if n.Body == nil || len(n.Body.List) == 0 {
return nil
}
case *ast.SwitchStmt:
// Don't annotate an empty switch - creates a syntax error.
if n.Body == nil || len(n.Body.List) == 0 {
if n.Init != nil {
ast.Walk(b, n.Init)
}
if n.Tag != nil {
ast.Walk(b, n.Tag)
}
return nil
}
case *ast.TypeSwitchStmt:
// Don't annotate an empty type switch - creates a syntax error.
if n.Body == nil || len(n.Body.List) == 0 {
if n.Init != nil {
ast.Walk(b, n.Init)
}
ast.Walk(b, n.Assign)
return nil
}
}
return b
}
// findText finds text in the original source, starting at pos.
// It correctly skips over comments and assumes it need not
// handle quoted strings.
// It returns a byte offset within f.src.
func (bs *BlockScanner) findText(pos token.Pos, text string) int {
b := []byte(text)
start := bs.offset(pos)
i := start
s := bs.content
for i < len(s) {
if bytes.HasPrefix(s[i:], b) {
return i
}
if i+2 <= len(s) && s[i] == '/' && s[i+1] == '/' {
for i < len(s) && s[i] != '\n' {
i++
}
continue
}
if i+2 <= len(s) && s[i] == '/' && s[i+1] == '*' {
for i += 2; ; i++ {
if i+2 > len(s) {
return 0
}
if s[i] == '*' && s[i+1] == '/' {
i += 2
break
}
}
continue
}
i++
}
return -1
}
// addCounters takes a list of statements and adds counters to the beginning of
// each basic block at the top level of that list. For instance, given
//
// S1
// if cond {
// S2
// }
// S3
//
// counters will be added before S1 and before S3. The block containing S2
// will be visited in a separate call.
// TODO: Nested simple blocks get unnecessary (but correct) counters
func (b *BlockScanner) addCounters(pos, insertPos, blockEnd token.Pos, list []ast.Stmt,
extendToClosingBrace bool) {
// Special case: make sure we add a counter to an empty block. Can't do this below
// or we will add a counter to an empty statement list after, say, a return statement.
if len(list) == 0 {
b.edit.Insert(b.offset(insertPos),
b.scanner(b.fset.Position(insertPos).Line, b.fset.Position(blockEnd).Line, b.blockNum))
b.blockNum++
return
}
// We have a block (statement list), but it may have several basic blocks due to the
// appearance of statements that affect the flow of control.
for {
// Find first statement that affects flow of control (break, continue, if, etc.).
// It will be the last statement of this basic block.
var last int
end := blockEnd
for last = 0; last < len(list); last++ {
stmt := list[last]
//fmt.Printf("%T\n", stmt)
end = b.statementBoundary(stmt)
if b.endsBasicSourceBlock(stmt) {
// If it is a labeled statement, we need to place a counter between
// the label and its statement because it may be the target of a goto
// and thus start a basic block. That is, given
// foo: stmt
// we need to create
// foo: ; stmt
// and mark the label as a block-terminating statement.
// The result will then be
// foo: COUNTER[n]++; stmt
// However, we can't do this if the labeled statement is already
// a control statement, such as a labeled for.
if label, isLabel := stmt.(*ast.LabeledStmt); isLabel && !b.isControl(label.Stmt) {
newLabel := *label
newLabel.Stmt = &ast.EmptyStmt{
Semicolon: label.Stmt.Pos(),
Implicit: true,
}
end = label.Pos() // Previous block ends before the label.
list[last] = &newLabel
// Open a gap and drop in the old statement, now without a label.
list = append(list, nil)
copy(list[last+1:], list[last:])
list[last+1] = label.Stmt
}
last++
extendToClosingBrace = false // Block is broken up now.
break
}
}
if extendToClosingBrace {
end = blockEnd
}
if pos != end { // Can have no source to cover if e.g. blocks abut.
b.edit.Insert(b.offset(insertPos),
b.scanner(b.fset.Position(insertPos).Line, b.fset.Position(end).Line,
b.blockNum))
b.blockNum++
}
list = list[last:]
if len(list) == 0 {
break
}
pos = list[0].Pos()
insertPos = pos
}
}
func (b *BlockScanner) offset(pos token.Pos) int {
return b.fset.Position(pos).Offset
}
func (b *BlockScanner) isControl(s ast.Stmt) bool {
switch s.(type) {
case *ast.ForStmt, *ast.RangeStmt, *ast.SwitchStmt, *ast.SelectStmt, *ast.TypeSwitchStmt:
return true
}
return false
}
// statementBoundary finds the location in s that terminates the current basic
// block in the source.
func (b *BlockScanner) statementBoundary(s ast.Stmt) token.Pos {
// Control flow statements are easy.
switch s := s.(type) {
case *ast.BlockStmt:
// Treat blocks like basic blocks to avoid overlapping counters.
return s.Lbrace
case *ast.IfStmt:
found, pos := hasFuncLiteral(s.Init)
if found {
return pos
}
found, pos = hasFuncLiteral(s.Cond)
if found {
return pos
}
return s.Body.Lbrace
case *ast.ForStmt:
found, pos := hasFuncLiteral(s.Init)
if found {
return pos
}
found, pos = hasFuncLiteral(s.Cond)
if found {
return pos
}
found, pos = hasFuncLiteral(s.Post)
if found {
return pos
}
return s.Body.Lbrace
case *ast.LabeledStmt:
return b.statementBoundary(s.Stmt)
case *ast.RangeStmt:
found, pos := hasFuncLiteral(s.X)
if found {
return pos
}
return s.Body.Lbrace
case *ast.SwitchStmt:
found, pos := hasFuncLiteral(s.Init)
if found {
return pos
}
found, pos = hasFuncLiteral(s.Tag)
if found {
return pos
}
return s.Body.Lbrace
case *ast.SelectStmt:
return s.Body.Lbrace
case *ast.TypeSwitchStmt:
found, pos := hasFuncLiteral(s.Init)
if found {
return pos
}
return s.Body.Lbrace
}
// If not a control flow statement, it is a declaration, expression, call, etc. and it may have a function literal.
// If it does, that's tricky because we want to exclude the body of the function from this block.
// Draw a line at the start of the body of the first function literal we find.
// TODO: what if there's more than one? Probably doesn't matter much.
found, pos := hasFuncLiteral(s)
if found {
return pos
}
return s.End()
}
// endsBasicSourceBlock reports whether s changes the flow of control: break, if, etc.,
// or if it's just problematic, for instance contains a function literal, which will complicate
// accounting due to the block-within-an expression.
func (f *BlockScanner) endsBasicSourceBlock(s ast.Stmt) bool {
switch s := s.(type) {
case *ast.BlockStmt:
// Treat blocks like basic blocks to avoid overlapping counters.
return true
case *ast.BranchStmt:
return true
case *ast.ForStmt:
return true
case *ast.IfStmt:
return true
case *ast.LabeledStmt:
return true // A goto may branch here, starting a new basic block.
case *ast.RangeStmt:
return true
case *ast.SwitchStmt:
return true
case *ast.SelectStmt:
return true
case *ast.TypeSwitchStmt:
return true
case *ast.ExprStmt:
// Calls to panic change the flow.
// We really should verify that "panic" is the predefined function,
// but without type checking we can't and the likelihood of it being
// an actual problem is vanishingly small.
if call, ok := s.X.(*ast.CallExpr); ok {
if ident, ok := call.Fun.(*ast.Ident); ok && ident.Name == "panic" && len(call.Args) == 1 {
return true
}
}
}
found, _ := hasFuncLiteral(s)
return found
}
// functon literal指匿名函数
// hasFuncLiteral reports the existence and position of the first func literal
// in the node, if any. If a func literal appears, it usually marks the termination
// of a basic block because the function body is itself a block.
// Therefore we draw a line at the start of the body of the first function literal we find.
// TODO: what if there's more than one? Probably doesn't matter much.
func hasFuncLiteral(n ast.Node) (bool, token.Pos) {
if n == nil {
return false, 0
}
var literal funcLitFinder
ast.Walk(&literal, n)
return literal.found(), token.Pos(literal)
}
// funcLitFinder implements the ast.Visitor pattern to find the location of any
// function literal in a subtree.
type funcLitFinder token.Pos
func (f *funcLitFinder) Visit(node ast.Node) (w ast.Visitor) {
if f.found() {
return nil // Prune search.
}
switch n := node.(type) {
case *ast.FuncLit:
*f = funcLitFinder(n.Body.Lbrace)
return nil // Prune search.
}
return f
}
func (f *funcLitFinder) found() bool {
return token.Pos(*f) != token.NoPos
}