1 files changed, 74 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/noder/posmap.go b/src/cmd/compile/internal/noder/posmap.go
new file mode 100644
index 0000000..439daf4
--- /dev/null
+++ b/src/cmd/compile/internal/noder/posmap.go
@@ -0,0 +1,74 @@
+// Copyright 2021 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.
+
+package noder
+
+import (
+	"cmd/compile/internal/base"
+	"cmd/compile/internal/syntax"
+	"cmd/internal/src"
+)
+
+// A posMap handles mapping from syntax.Pos to src.XPos.
+type posMap struct {
+	bases map[*syntax.PosBase]*src.PosBase
+	cache struct {
+		last *syntax.PosBase
+		base *src.PosBase
+	}
+}
+
+type poser interface{ Pos() syntax.Pos }
+type ender interface{ End() syntax.Pos }
+
+func (m *posMap) pos(p poser) src.XPos { return m.makeXPos(p.Pos()) }
+func (m *posMap) end(p ender) src.XPos { return m.makeXPos(p.End()) }
+
+func (m *posMap) makeXPos(pos syntax.Pos) src.XPos {
+	// Predeclared objects (e.g., the result parameter for error.Error)
+	// do not have a position.
+	if !pos.IsKnown() {
+		return src.NoXPos
+	}
+
+	posBase := m.makeSrcPosBase(pos.Base())
+	return base.Ctxt.PosTable.XPos(src.MakePos(posBase, pos.Line(), pos.Col()))
+}
+
+// makeSrcPosBase translates from a *syntax.PosBase to a *src.PosBase.
+func (m *posMap) makeSrcPosBase(b0 *syntax.PosBase) *src.PosBase {
+	// fast path: most likely PosBase hasn't changed
+	if m.cache.last == b0 {
+		return m.cache.base
+	}
+
+	b1, ok := m.bases[b0]
+	if !ok {
+		fn := b0.Filename()
+		absfn := trimFilename(b0)
+
+		if b0.IsFileBase() {
+			b1 = src.NewFileBase(fn, absfn)
+		} else {
+			// line directive base
+			p0 := b0.Pos()
+			p0b := p0.Base()
+			if p0b == b0 {
+				panic("infinite recursion in makeSrcPosBase")
+			}
+			p1 := src.MakePos(m.makeSrcPosBase(p0b), p0.Line(), p0.Col())
+			b1 = src.NewLinePragmaBase(p1, fn, absfn, b0.Line(), b0.Col())
+		}
+		if m.bases == nil {
+			m.bases = make(map[*syntax.PosBase]*src.PosBase)
+		}
+		m.bases[b0] = b1
+	}
+
+	// update cache
+	m.cache.last = b0
+	m.cache.base = b1
+
+	return b1
+}