gtsocial-umbx

pos.go (15759B)

---

 // Copyright 2016 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // This file implements the encoding of source positions.
 
 package src
 
 import (
 	"bytes"
 	"fmt"
 	"io"
 )
 
 // A Pos encodes a source position consisting of a (line, column) number pair
 // and a position base. A zero Pos is a ready to use "unknown" position (nil
 // position base and zero line number).
 //
 // The (line, column) values refer to a position in a file independent of any
 // position base ("absolute" file position).
 //
 // The position base is used to determine the "relative" position, that is the
 // filename and line number relative to the position base. If the base refers
 // to the current file, there is no difference between absolute and relative
 // positions. If it refers to a //line directive, a relative position is relative
 // to that directive. A position base in turn contains the position at which it
 // was introduced in the current file.
 type Pos struct {
 	base *PosBase
 	lico
 }
 
 // NoPos is a valid unknown position.
 var NoPos Pos
 
 // MakePos creates a new Pos value with the given base, and (file-absolute)
 // line and column.
 func MakePos(base *PosBase, line, col uint) Pos {
 	return Pos{base, makeLico(line, col)}
 }
 
 // IsKnown reports whether the position p is known.
 // A position is known if it either has a non-nil
 // position base, or a non-zero line number.
 func (p Pos) IsKnown() bool {
 	return p.base != nil || p.Line() != 0
 }
 
 // Before reports whether the position p comes before q in the source.
 // For positions in different files, ordering is by filename.
 func (p Pos) Before(q Pos) bool {
 	n, m := p.Filename(), q.Filename()
 	return n < m || n == m && p.lico < q.lico
 }
 
 // After reports whether the position p comes after q in the source.
 // For positions in different files, ordering is by filename.
 func (p Pos) After(q Pos) bool {
 	n, m := p.Filename(), q.Filename()
 	return n > m || n == m && p.lico > q.lico
 }
 
 func (p Pos) LineNumber() string {
 	if !p.IsKnown() {
 		return "?"
 	}
 	return p.lico.lineNumber()
 }
 
 func (p Pos) LineNumberHTML() string {
 	if !p.IsKnown() {
 		return "?"
 	}
 	return p.lico.lineNumberHTML()
 }
 
 // Filename returns the name of the actual file containing this position.
 func (p Pos) Filename() string { return p.base.Pos().RelFilename() }
 
 // Base returns the position base.
 func (p Pos) Base() *PosBase { return p.base }
 
 // SetBase sets the position base.
 func (p *Pos) SetBase(base *PosBase) { p.base = base }
 
 // RelFilename returns the filename recorded with the position's base.
 func (p Pos) RelFilename() string { return p.base.Filename() }
 
 // RelLine returns the line number relative to the position's base.
 func (p Pos) RelLine() uint {
 	b := p.base
 	if b.Line() == 0 {
 		// base line is unknown => relative line is unknown
 		return 0
 	}
 	return b.Line() + (p.Line() - b.Pos().Line())
 }
 
 // RelCol returns the column number relative to the position's base.
 func (p Pos) RelCol() uint {
 	b := p.base
 	if b.Col() == 0 {
 		// base column is unknown => relative column is unknown
 		// (the current specification for line directives requires
 		// this to apply until the next PosBase/line directive,
 		// not just until the new newline)
 		return 0
 	}
 	if p.Line() == b.Pos().Line() {
 		// p on same line as p's base => column is relative to p's base
 		return b.Col() + (p.Col() - b.Pos().Col())
 	}
 	return p.Col()
 }
 
 // AbsFilename() returns the absolute filename recorded with the position's base.
 func (p Pos) AbsFilename() string { return p.base.AbsFilename() }
 
 // SymFilename() returns the absolute filename recorded with the position's base,
 // prefixed by FileSymPrefix to make it appropriate for use as a linker symbol.
 func (p Pos) SymFilename() string { return p.base.SymFilename() }
 
 func (p Pos) String() string {
 	return p.Format(true, true)
 }
 
 // Format formats a position as "filename:line" or "filename:line:column",
 // controlled by the showCol flag and if the column is known (!= 0).
 // For positions relative to line directives, the original position is
 // shown as well, as in "filename:line[origfile:origline:origcolumn] if
 // showOrig is set.
 func (p Pos) Format(showCol, showOrig bool) string {
 	buf := new(bytes.Buffer)
 	p.WriteTo(buf, showCol, showOrig)
 	return buf.String()
 }
 
 // WriteTo a position to w, formatted as Format does.
 func (p Pos) WriteTo(w io.Writer, showCol, showOrig bool) {
 	if !p.IsKnown() {
 		io.WriteString(w, "<unknown line number>")
 		return
 	}
 
 	if b := p.base; b == b.Pos().base {
 		// base is file base (incl. nil)
 		format(w, p.Filename(), p.Line(), p.Col(), showCol)
 		return
 	}
 
 	// base is relative
 	// Print the column only for the original position since the
 	// relative position's column information may be bogus (it's
 	// typically generated code and we can't say much about the
 	// original source at that point but for the file:line info
 	// that's provided via a line directive).
 	// TODO(gri) This may not be true if we have an inlining base.
 	// We may want to differentiate at some point.
 	format(w, p.RelFilename(), p.RelLine(), p.RelCol(), showCol)
 	if showOrig {
 		io.WriteString(w, "[")
 		format(w, p.Filename(), p.Line(), p.Col(), showCol)
 		io.WriteString(w, "]")
 	}
 }
 
 // format formats a (filename, line, col) tuple as "filename:line" (showCol
 // is false or col == 0) or "filename:line:column" (showCol is true and col != 0).
 func format(w io.Writer, filename string, line, col uint, showCol bool) {
 	io.WriteString(w, filename)
 	io.WriteString(w, ":")
 	fmt.Fprint(w, line)
 	// col == 0 and col == colMax are interpreted as unknown column values
 	if showCol && 0 < col && col < colMax {
 		io.WriteString(w, ":")
 		fmt.Fprint(w, col)
 	}
 }
 
 // formatstr wraps format to return a string.
 func formatstr(filename string, line, col uint, showCol bool) string {
 	buf := new(bytes.Buffer)
 	format(buf, filename, line, col, showCol)
 	return buf.String()
 }
 
 // ----------------------------------------------------------------------------
 // PosBase
 
 // A PosBase encodes a filename and base position.
 // Typically, each file and line directive introduce a PosBase.
 type PosBase struct {
 	pos         Pos    // position at which the relative position is (line, col)
 	filename    string // file name used to open source file, for error messages
 	absFilename string // absolute file name, for PC-Line tables
 	symFilename string // cached symbol file name, to avoid repeated string concatenation
 	line, col   uint   // relative line, column number at pos
 	inl         int    // inlining index (see cmd/internal/obj/inl.go)
 }
 
 // NewFileBase returns a new *PosBase for a file with the given (relative and
 // absolute) filenames.
 func NewFileBase(filename, absFilename string) *PosBase {
 	base := &PosBase{
 		filename:    filename,
 		absFilename: absFilename,
 		symFilename: FileSymPrefix + absFilename,
 		line:        1,
 		col:         1,
 		inl:         -1,
 	}
 	base.pos = MakePos(base, 1, 1)
 	return base
 }
 
 // NewLinePragmaBase returns a new *PosBase for a line directive of the form
 //      //line filename:line:col
 //      /*line filename:line:col*/
 // at position pos.
 func NewLinePragmaBase(pos Pos, filename, absFilename string, line, col uint) *PosBase {
 	return &PosBase{pos, filename, absFilename, FileSymPrefix + absFilename, line, col, -1}
 }
 
 // NewInliningBase returns a copy of the old PosBase with the given inlining
 // index. If old == nil, the resulting PosBase has no filename.
 func NewInliningBase(old *PosBase, inlTreeIndex int) *PosBase {
 	if old == nil {
 		base := &PosBase{line: 1, col: 1, inl: inlTreeIndex}
 		base.pos = MakePos(base, 1, 1)
 		return base
 	}
 	copy := *old
 	base := &copy
 	base.inl = inlTreeIndex
 	if old == old.pos.base {
 		base.pos.base = base
 	}
 	return base
 }
 
 var noPos Pos
 
 // Pos returns the position at which base is located.
 // If b == nil, the result is the zero position.
 func (b *PosBase) Pos() *Pos {
 	if b != nil {
 		return &b.pos
 	}
 	return &noPos
 }
 
 // Filename returns the filename recorded with the base.
 // If b == nil, the result is the empty string.
 func (b *PosBase) Filename() string {
 	if b != nil {
 		return b.filename
 	}
 	return ""
 }
 
 // AbsFilename returns the absolute filename recorded with the base.
 // If b == nil, the result is the empty string.
 func (b *PosBase) AbsFilename() string {
 	if b != nil {
 		return b.absFilename
 	}
 	return ""
 }
 
 const FileSymPrefix = "gofile.."
 
 // SymFilename returns the absolute filename recorded with the base,
 // prefixed by FileSymPrefix to make it appropriate for use as a linker symbol.
 // If b is nil, SymFilename returns FileSymPrefix + "??".
 func (b *PosBase) SymFilename() string {
 	if b != nil {
 		return b.symFilename
 	}
 	return FileSymPrefix + "??"
 }
 
 // Line returns the line number recorded with the base.
 // If b == nil, the result is 0.
 func (b *PosBase) Line() uint {
 	if b != nil {
 		return b.line
 	}
 	return 0
 }
 
 // Col returns the column number recorded with the base.
 // If b == nil, the result is 0.
 func (b *PosBase) Col() uint {
 	if b != nil {
 		return b.col
 	}
 	return 0
 }
 
 // InliningIndex returns the index into the global inlining
 // tree recorded with the base. If b == nil or the base has
 // not been inlined, the result is < 0.
 func (b *PosBase) InliningIndex() int {
 	if b != nil {
 		return b.inl
 	}
 	return -1
 }
 
 // ----------------------------------------------------------------------------
 // lico
 
 // A lico is a compact encoding of a LIne and COlumn number.
 type lico uint32
 
 // Layout constants: 20 bits for line, 8 bits for column, 2 for isStmt, 2 for pro/epilogue
 // (If this is too tight, we can either make lico 64b wide,
 // or we can introduce a tiered encoding where we remove column
 // information as line numbers grow bigger; similar to what gcc
 // does.)
 // The bitfield order is chosen to make IsStmt be the least significant
 // part of a position; its use is to communicate statement edges through
 // instruction scrambling in code generation, not to impose an order.
 // TODO: Prologue and epilogue are perhaps better handled as pseudo-ops for the assembler,
 // because they have almost no interaction with other uses of the position.
 const (
 	lineBits, lineMax     = 20, 1<<lineBits - 2
 	bogusLine             = 1 // Used to disrupt infinite loops to prevent debugger looping
 	isStmtBits, isStmtMax = 2, 1<<isStmtBits - 1
 	xlogueBits, xlogueMax = 2, 1<<xlogueBits - 1
 	colBits, colMax       = 32 - lineBits - xlogueBits - isStmtBits, 1<<colBits - 1
 
 	isStmtShift = 0
 	isStmtMask  = isStmtMax << isStmtShift
 	xlogueShift = isStmtBits + isStmtShift
 	xlogueMask  = xlogueMax << xlogueShift
 	colShift    = xlogueBits + xlogueShift
 	lineShift   = colBits + colShift
 )
 const (
 	// It is expected that the front end or a phase in SSA will usually generate positions tagged with
 	// PosDefaultStmt, but note statement boundaries with PosIsStmt.  Simple statements will have a single
 	// boundary; for loops with initialization may have one for their entry and one for their back edge
 	// (this depends on exactly how the loop is compiled; the intent is to provide a good experience to a
 	// user debugging a program; the goal is that a breakpoint set on the loop line fires both on entry
 	// and on iteration).  Proper treatment of non-gofmt input with multiple simple statements on a single
 	// line is TBD.
 	//
 	// Optimizing compilation will move instructions around, and some of these will become known-bad as
 	// step targets for debugging purposes (examples: register spills and reloads; code generated into
 	// the entry block; invariant code hoisted out of loops) but those instructions will still have interesting
 	// positions for profiling purposes. To reflect this these positions will be changed to PosNotStmt.
 	//
 	// When the optimizer removes an instruction marked PosIsStmt; it should attempt to find a nearby
 	// instruction with the same line marked PosDefaultStmt to be the new statement boundary.  I.e., the
 	// optimizer should make a best-effort to conserve statement boundary positions, and might be enhanced
 	// to note when a statement boundary is not conserved.
 	//
 	// Code cloning, e.g. loop unrolling or loop unswitching, is an exception to the conservation rule
 	// because a user running a debugger would expect to see breakpoints active in the copies of the code.
 	//
 	// In non-optimizing compilation there is still a role for PosNotStmt because of code generation
 	// into the entry block.  PosIsStmt statement positions should be conserved.
 	//
 	// When code generation occurs any remaining default-marked positions are replaced with not-statement
 	// positions.
 	//
 	PosDefaultStmt uint = iota // Default; position is not a statement boundary, but might be if optimization removes the designated statement boundary
 	PosIsStmt                  // Position is a statement boundary; if optimization removes the corresponding instruction, it should attempt to find a new instruction to be the boundary.
 	PosNotStmt                 // Position should not be a statement boundary, but line should be preserved for profiling and low-level debugging purposes.
 )
 
 type PosXlogue uint
 
 const (
 	PosDefaultLogue PosXlogue = iota
 	PosPrologueEnd
 	PosEpilogueBegin
 )
 
 func makeLicoRaw(line, col uint) lico {
 	return lico(line<<lineShift | col<<colShift)
 }
 
 // This is a not-position that will not be elided.
 // Depending on the debugger (gdb or delve) it may or may not be displayed.
 func makeBogusLico() lico {
 	return makeLicoRaw(bogusLine, 0).withIsStmt()
 }
 
 func makeLico(line, col uint) lico {
 	if line > lineMax {
 		// cannot represent line, use max. line so we have some information
 		line = lineMax
 	}
 	if col > colMax {
 		// cannot represent column, use max. column so we have some information
 		col = colMax
 	}
 	// default is not-sure-if-statement
 	return makeLicoRaw(line, col)
 }
 
 func (x lico) Line() uint           { return uint(x) >> lineShift }
 func (x lico) SameLine(y lico) bool { return 0 == (x^y)&^lico(1<<lineShift-1) }
 func (x lico) Col() uint            { return uint(x) >> colShift & colMax }
 func (x lico) IsStmt() uint {
 	if x == 0 {
 		return PosNotStmt
 	}
 	return uint(x) >> isStmtShift & isStmtMax
 }
 func (x lico) Xlogue() PosXlogue {
 	return PosXlogue(uint(x) >> xlogueShift & xlogueMax)
 }
 
 // withNotStmt returns a lico for the same location, but not a statement
 func (x lico) withNotStmt() lico {
 	return x.withStmt(PosNotStmt)
 }
 
 // withDefaultStmt returns a lico for the same location, with default isStmt
 func (x lico) withDefaultStmt() lico {
 	return x.withStmt(PosDefaultStmt)
 }
 
 // withIsStmt returns a lico for the same location, tagged as definitely a statement
 func (x lico) withIsStmt() lico {
 	return x.withStmt(PosIsStmt)
 }
 
 // withLogue attaches a prologue/epilogue attribute to a lico
 func (x lico) withXlogue(xlogue PosXlogue) lico {
 	if x == 0 {
 		if xlogue == 0 {
 			return x
 		}
 		// Normalize 0 to "not a statement"
 		x = lico(PosNotStmt << isStmtShift)
 	}
 	return lico(uint(x) & ^uint(xlogueMax<<xlogueShift) | (uint(xlogue) << xlogueShift))
 }
 
 // withStmt returns a lico for the same location with specified is_stmt attribute
 func (x lico) withStmt(stmt uint) lico {
 	if x == 0 {
 		return lico(0)
 	}
 	return lico(uint(x) & ^uint(isStmtMax<<isStmtShift) | (stmt << isStmtShift))
 }
 
 func (x lico) lineNumber() string {
 	return fmt.Sprintf("%d", x.Line())
 }
 
 func (x lico) lineNumberHTML() string {
 	if x.IsStmt() == PosDefaultStmt {
 		return fmt.Sprintf("%d", x.Line())
 	}
 	style, pfx := "b", "+"
 	if x.IsStmt() == PosNotStmt {
 		style = "s" // /strike not supported in HTML5
 		pfx = ""
 	}
 	return fmt.Sprintf("<%s>%s%d</%s>", style, pfx, x.Line(), style)
 }
 
 func (x lico) atColumn1() lico {
 	return makeLico(x.Line(), 1).withIsStmt()
 }