cmd/compile: fix position info for implicit nodes due to generics

The main fix is that we should call ir.SetPos() at the beginning of
(*subster).node.edit function, since that is analogous to the
ir.SetPos() at the beginning of typecheck.typecheck(). It ensures that
transform functions can use base.Pos() with appropriate results, just
like their corresponding tc*() functions do.

A small fix is to make sure that the new nodes creates for dictionary
references have the correct position based on the location of the
function call.

Another small fix is to the use of base.Pos when creating a new selector
expression (including implicit XDOTs) for a method expression in
buildClosure().

Also, I converted the final use of base.Pos in stencil.go to src.NoXPos,
since the nodes created by AddImplicitDots will be checked for their
type, but won't actually be used.

I also needed to add an ir.SetPos() at the beginning of transformCall(),
since transformCall() is called in the modify and dict passes, when we
base.Pos is not being set for each node.

This change fixes all the line numbering problems printed out from
Alessandro's program, except for auto-generated functions (which I think
are fine).

Fixes #49523

Change-Id: I9836a497b7beba25ecafdde653a6c2036a3020d3
Reviewed-on: https://go-review.googlesource.com/c/go/+/363835
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/noder/transform.go b/src/cmd/compile/internal/noder/transform.go
index 47e6397206..a673484821 100644
--- a/src/cmd/compile/internal/noder/transform.go
+++ b/src/cmd/compile/internal/noder/transform.go
@@ -133,6 +133,9 @@ func transformConvCall(n *ir.CallExpr) ir.Node {
 // (non-conversion, non-builtin part) of typecheck.tcCall. This code should work even
 // in the case of OCALL/OFUNCINST.
 func transformCall(n *ir.CallExpr) {
+	// Set base.Pos, since transformArgs below may need it, but transformCall
+	// is called in some passes that don't set base.Pos.
+	ir.SetPos(n)
 	// n.Type() can be nil for calls with no return value
 	assert(n.Typecheck() == 1)
 	transformArgs(n)