// All node types implement the Node interface. type Node interface { Pos() token.Pos // position of first character belonging to the node End() token.Pos // position of first character immediately after the node }
// All expression nodes implement the Expr interface. type Expr interface { Node exprNode() }
// All statement nodes implement the Stmt interface. type Stmt interface { Node stmtNode() }
// All declaration nodes implement the Decl interface. type Decl interface { Node declNode() }
// The parser structure holds the parser's internal state. type parser struct { file *token.File errors scanner.ErrorList // 解析过程中遇到的错误列表 scanner scanner.Scanner // 词法分析器.
// Tracing/debugging mode Mode // parsing mode // 解析模式 trace bool // == (mode & Trace != 0) indent int // indentation used for tracing output
// Comments 列表 comments []*ast.CommentGroup leadComment *ast.CommentGroup // last lead comment lineComment *ast.CommentGroup // last line comment
// Next token pos token.Pos // token position tok token.Token // one token look-ahead lit string // token literal
// Error recovery // (used to limit the number of calls to syncXXX functions // w/o making scanning progress - avoids potential endless // loops across multiple parser functions during error recovery) syncPos token.Pos // last synchronization position 解析错误的同步点. syncCnt int // number of calls to syncXXX without progress
// Non-syntactic parser control // 非语法性的控制 // <0 在控制语句中, >= 在表达式中. exprLev int // < 0: in control clause, >= 0: in expression // 正在解析右值表达式 inRhs bool // if set, the parser is parsing a rhs expression
// Ordinary identifier scopes pkgScope *ast.Scope // pkgScope.Outer == nil topScope *ast.Scope // top-most scope; may be pkgScope unresolved []*ast.Ident // unresolved identifiers imports []*ast.ImportSpec // list of imports
// Label scopes // (maintained by open/close LabelScope) labelScope *ast.Scope // label scope for current function targetStack [][]*ast.Ident // stack of unresolved labels }
func (p *parser) parseStmt() (s ast.Stmt) { if p.trace { defer un(trace(p, "Statement")) }
switch p.tok { case token.CONST, token.TYPE, token.VAR: s = &ast.DeclStmt{Decl: p.parseDecl(syncStmt)} case // tokens that may start an expression token.IDENT, token.INT, token.FLOAT, token.IMAG, token.CHAR, token.STRING, token.FUNC, token.LPAREN, // operands token.LBRACK, token.STRUCT, token.MAP, token.CHAN, token.INTERFACE, // composite types token.ADD, token.SUB, token.MUL, token.AND, token.XOR, token.ARROW, token.NOT: // unary operators s, _ = p.parseSimpleStmt(labelOk) // because of the required look-ahead, labeled statements are // parsed by parseSimpleStmt - don't expect a semicolon after // them if _, isLabeledStmt := s.(*ast.LabeledStmt); !isLabeledStmt { p.expectSemi() } case token.GO: s = p.parseGoStmt() case token.DEFER: s = p.parseDeferStmt() case token.RETURN: s = p.parseReturnStmt() case token.BREAK, token.CONTINUE, token.GOTO, token.FALLTHROUGH: s = p.parseBranchStmt(p.tok) case token.LBRACE: s = p.parseBlockStmt() ...省略
// 解析左列表 一般是 l := r 或者 l1,l2 = r1,r2 或者 l <- r 或者 l++ x := p.parseLhsList() switch p.tok { case token.DEFINE, token.ASSIGN, token.ADD_ASSIGN, token.SUB_ASSIGN, token.MUL_ASSIGN, token.QUO_ASSIGN, token.REM_ASSIGN, token.AND_ASSIGN, token.OR_ASSIGN, token.XOR_ASSIGN, token.SHL_ASSIGN, token.SHR_ASSIGN, token.AND_NOT_ASSIGN: // 如果看到range,range作为一种运算符按照range rhs来解析 // 如果没看到就按正常赋值语句解析 lhs op rhs 来解析op可以是上面那些token中的一种. pos, tok := p.pos, p.tok p.next() var y []ast.Expr isRange := false if mode == rangeOk && p.tok == token.RANGE && (tok == token.DEFINE || tok == token.ASSIGN) { pos := p.pos p.next() y = []ast.Expr{&ast.UnaryExpr{OpPos: pos, Op: token.RANGE, X: p.parseRhs()}} isRange = true } else { y = p.parseRhsList() } as := &ast.AssignStmt{Lhs: x, TokPos: pos, Tok: tok, Rhs: y}
// 碰到":"找一个ident, 构成 goto: indent 之类的语句. case token.COLON: colon := p.pos p.next() if label, isIdent := x[0].(*ast.Ident); mode == labelOk && isIdent { // Go spec: The scope of a label is the body of the function // in which it is declared and excludes the body of any nested // function. stmt := &ast.LabeledStmt{Label: label, Colon: colon, Stmt: p.parseStmt()} p.declare(stmt, nil, p.labelScope, ast.Lbl, label) return stmt, false } // 碰到"<-",就构成 <- rhs 这样的语句. case token.ARROW: // send statement arrow := p.pos p.next() y := p.parseRhs() return &ast.SendStmt{Chan: x[0], Arrow: arrow, Value: y}, false
// 碰到"++"或者"--"就构成一个单独的自增语句. case token.INC, token.DEC: // increment or decrement s := &ast.IncDecStmt{X: x[0], TokPos: p.pos, Tok: p.tok} p.next() return s, false }
