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trim.go
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trim.go
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package discover
import "go/ast"
// Trim trims the AST rooted at node based on the coverage profile,
// removing irrelevant and unreached parts of the program.
// If the node is an *ast.File, comments are updated as well using
// an ast.CommentMap.
func (p *Profile) Trim(node ast.Node) {
if f, ok := node.(*ast.File); ok {
cmap := ast.NewCommentMap(p.Fset, f, f.Comments)
ast.Walk(&trimVisitor{p}, f)
f.Comments = cmap.Filter(f).Comments()
} else {
ast.Walk(&trimVisitor{p}, node)
}
}
// trimVisitor is an ast.Visitor that trims nodes as it walks the tree.
type trimVisitor struct {
p *Profile
}
func (v *trimVisitor) Visit(node ast.Node) ast.Visitor {
var list *[]ast.Stmt
switch node := node.(type) {
case *ast.File:
var replaced []ast.Decl
for _, decl := range node.Decls {
// Remove non-func declarations and funcs that were not covered
if f, ok := decl.(*ast.FuncDecl); ok && v.p.Funcs[f] {
replaced = append(replaced, decl)
}
}
node.Decls = replaced
// Node types containing lists of statements
case *ast.BlockStmt:
list = &node.List
case *ast.CommClause:
list = &node.Body
case *ast.CaseClause:
list = &node.Body
}
if list != nil {
var replaced []ast.Stmt
for _, stmt := range *list {
replaced = append(replaced, v.replaceStmt(stmt)...)
}
*list = replaced
}
return v
}
// replaceStmt returns the (possibly many) statements that should replace
// stmt. Generally a stmt is untouched or removed, but in some cases a
// single stmt can result in multiple statements. This is usually only the case
// when removing a block that was not taken, but pulling out function calls
// that were part of the initialization of the block.
func (v *trimVisitor) replaceStmt(stmt ast.Stmt) []ast.Stmt {
switch stmt := stmt.(type) {
case nil:
return nil
default:
// Keep original
return []ast.Stmt{stmt}
case *ast.RangeStmt:
if v.visited(stmt.Body) {
return []ast.Stmt{stmt}
}
call := v.findCall(stmt.X)
if call != nil {
return []ast.Stmt{&ast.ExprStmt{call}}
}
return nil
case *ast.ForStmt:
if v.visited(stmt.Body) {
return []ast.Stmt{stmt}
}
nodes := []*ast.CallExpr{
v.findCall(stmt.Init),
v.findCall(stmt.Cond),
v.findCall(stmt.Post),
}
var result []ast.Stmt
for _, call := range nodes {
if call != nil {
result = append(result, &ast.ExprStmt{call})
}
}
return result
case *ast.IfStmt:
vIf := v.visited(stmt.Body)
vElse := v.visited(stmt.Else)
if !vIf {
var result []ast.Stmt
// If we didn't reach the body, pull out any calls from
// init and cond.
nodes := []*ast.CallExpr{
v.findCall(stmt.Init),
v.findCall(stmt.Cond),
}
for _, call := range nodes {
if call != nil {
result = append(result, &ast.ExprStmt{call})
}
}
if vElse {
// We reached the else; add it
if block, ok := stmt.Else.(*ast.BlockStmt); ok {
// For a block statement, add the statements individually
// so we don't end up with an unnecessary block
for _, stmt := range block.List {
result = append(result, v.replaceStmt(stmt)...)
}
} else {
result = append(result, v.replaceStmt(stmt.Else)...)
}
}
return result
} else {
// We did take the if body
if !vElse {
// But not the else: remove it
stmt.Else = nil
}
return []ast.Stmt{stmt}
}
case *ast.SelectStmt:
var list []ast.Stmt
for _, stmt := range stmt.Body.List {
if v.visited(stmt) {
list = append(list, stmt)
}
}
stmt.Body.List = list
return []ast.Stmt{stmt}
case *ast.SwitchStmt:
var list []ast.Stmt
for _, stmt := range stmt.Body.List {
if v.visitedAndMatters(stmt) {
list = append(list, stmt)
}
}
// If we didn't visit any case clauses, don't add the select at all.
if len(list) == 0 {
return nil
} else {
stmt.Body.List = list
return []ast.Stmt{stmt}
}
case *ast.TypeSwitchStmt:
var list []ast.Stmt
for _, stmt := range stmt.Body.List {
if v.visitedAndMatters(stmt) {
list = append(list, stmt)
}
}
// If we didn't visit any case clauses, don't add the select at all.
if len(list) == 0 {
return nil
} else {
stmt.Body.List = list
return []ast.Stmt{stmt}
}
}
}
// visited is a helper function to return whether or not a statement
// was visited. If stmt is nil, visited returns false.
func (v *trimVisitor) visited(stmt ast.Stmt) bool {
if stmt == nil { // for convenience with e.g. IfStmt.Else
return false
}
return v.p.Stmts[stmt]
}
// visitedAndMatters is like visited, but also checks that the statement
// has any effect. For example, an empty block has no effect and thus
// is considered to not matter, even though it may have been visited.
func (v *trimVisitor) visitedAndMatters(stmt ast.Stmt) bool {
if !v.visited(stmt) {
return false
}
switch stmt := stmt.(type) {
default:
// By default, statements matter
return true
case *ast.EmptyStmt:
// Empty statements do not matter
return false
case *ast.BlockStmt:
// Blocks matter if and only if any of the containing statements
// matter.
for _, stmt := range stmt.List {
if v.visitedAndMatters(stmt) {
return true
}
}
return false
case *ast.CaseClause:
for _, stmt := range stmt.Body {
if v.visitedAndMatters(stmt) {
return true
}
}
return false
}
}
// findCall returns the first *ast.CallExpr encountered within the tree
// rooted at node, or nil if no CallExpr was found. This is useful for
// "pulling out" calls out of a statement or expression.
func (v *trimVisitor) findCall(node ast.Node) *ast.CallExpr {
if node == nil { // for convenience
return nil
}
var call *ast.CallExpr
ast.Inspect(node, func(n ast.Node) bool {
if call != nil {
return false
}
c, ok := n.(*ast.CallExpr)
if ok {
call = c
return false
}
return true
})
return call
}