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cmd/compile/internal/syntax: establish principled position information

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Until now, the parser set the position for each Node to the position of
the first token belonging to that node. For compatibility with the now
defunct gc parser, in many places that position information was modified
when the gcCompat flag was set (which it was, by default). Furthermore,
in some places, position information was not set at all.

This change removes the gcCompat flag and all associated code, and sets
position information for all nodes in a more principled way, as proposed
by mdempsky (see #16943 for details). Specifically, the position of a
node may not be at the very beginning of the respective production. For
instance for an Operation `a + b`, the position associated with the node
is the position of the `+`. Thus, for `a + b + c` we now get different
positions for the two additions.

This change does not pass toolstash -cmp because position information
recorded in export data and pcline tables is different. There are no
other functional changes.

Added test suite testing the position of all nodes.

Fixes #16943.

Change-Id: I3fc02bf096bc3b3d7d2fa655dfd4714a1a0eb90c
Reviewed-on: https://go-review.googlesource.com/37017
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Robert Griesemer 2017-02-13 16:00:53 -08:00
parent 6910756f9b
commit 5267ac2732
4 changed files with 466 additions and 172 deletions
Download patch file Download diff file Expand all files Collapse all files

14
src/cmd/compile/internal/syntax/nodes.go
View file

@ -10,9 +10,16 @@ import "cmd/internal/src"
// Nodes
type Node interface {
// Pos() returns the position associated with the node as follows:
// 1) The position of a node representing a terminal syntax production
// (Name, BasicLit, etc.) is the position of the respective production
// in the source.
// 2) The position of a node representing a non-terminal production
// (IndexExpr, IfStmt, etc.) is the position of a token uniquely
// associated with that production; usually the left-most one
// ('[' for IndexExpr, 'if' for IfStmt, etc.)
Pos() src.Pos
aNode()
init(p *parser)
}
type node struct {
@ -27,11 +34,6 @@ func (n *node) Pos() src.Pos {
func (*node) aNode() {}
// TODO(gri) we may be able to get rid of init here and in Node
func (n *node) init(p *parser) {
n.pos = p.pos()
}
// ----------------------------------------------------------------------------
// Files