Implement diag.Diagable on MuIL AST nodes

This ensures that source context information flows automatically from
MuIL AST nodes to the various diag-related functions.

pkg/diag/pos.go

@@ -4,8 +4,8 @@ package diag
 
 // Pos represents a position in a file.
 type Pos struct {
-	Ln  int
-	Col int
+	Line   int // a 1-based line number
+	Column int // a 0-based column number
 }
 
 // EmptyPos may be used when no position is needed.
@@ -13,19 +13,19 @@ var EmptyPos = Pos{0, 0}
 
 // IsEmpty returns true if the Pos information is missing.
 func (pos Pos) IsEmpty() bool {
-	return pos.Ln == 0 && pos.Col == 0
+	return pos.Line == 0 && pos.Column == 0
 }
 
 // Location represents a region spanning two positions in a file.
 type Location struct {
-	From Pos
-	To   Pos
+	Start Pos  // a starting position.
+	End   *Pos // an ending position; if nil, represents a point.
 }
 
 // EmptyLocation may be used when no position information is available.
-var EmptyLocation = Location{EmptyPos, EmptyPos}
+var EmptyLocation = Location{EmptyPos, nil}
 
 // IsEmpty returns true if the Location information is missing.
 func (loc Location) IsEmpty() bool {
-	return loc.From.IsEmpty() && loc.To.IsEmpty()
+	return loc.Start.IsEmpty() && (loc.End == nil || loc.End.IsEmpty())
 }

pkg/diag/sink.go

@@ -114,9 +114,9 @@ func (d *defaultSink) Stringify(diag *Diag, prefix string, args ...interface{})
 
 		if diag.Loc != nil && !diag.Loc.IsEmpty() {
 			buffer.WriteRune(':')
-			buffer.WriteString(strconv.Itoa(diag.Loc.From.Ln))
+			buffer.WriteString(strconv.Itoa(diag.Loc.Start.Line))
 			buffer.WriteRune(':')
-			buffer.WriteString(strconv.Itoa(diag.Loc.From.Col))
+			buffer.WriteString(strconv.Itoa(diag.Loc.Start.Column))
 		}
 		buffer.WriteString(": ")
 	}

pkg/pack/ast/nodes.go

@@ -11,6 +11,7 @@
 package ast
 
 import (
+	"github.com/marapongo/mu/pkg/diag"
 	"github.com/marapongo/mu/pkg/symbols"
 )
 
@@ -30,10 +31,34 @@ type node struct {
 	Loc  *Location `json:"loc,omitempty"`
 }
 
+var _ diag.Diagable = (*node)(nil)
+
 func (node *node) nd()               {}
 func (node *node) GetKind() NodeKind { return node.Kind }
 func (node *node) GetLoc() *Location { return node.Loc }
 
+func (node *node) Where() (*diag.Document, *diag.Location) {
+	// TODO: consider caching Document objects; allocating one per Node is wasteful.
+	// TODO: for development scenarios, it would be really great to recover the original source file text for purposes
+	//     of the diag.Document part.  Doing so would give nice error messages tied back to the original source code
+	//     for any errors associated with the AST.  Absent that, we will simply return nil.
+	if node.Loc == nil {
+		return nil, nil
+	} else {
+		var doc *diag.Document
+		if node.Loc.File != nil {
+			doc = diag.NewDocument(*node.Loc.File)
+		}
+		var end *diag.Pos
+		if node.Loc.End != nil {
+			end = &diag.Pos{int(node.Loc.End.Line), int(node.Loc.End.Column)}
+		}
+		return doc, &diag.Location{
+			diag.Pos{int(node.Loc.Start.Line), int(node.Loc.Start.Column)}, end,
+		}
+	}
+}
+
 // Identifier represents a simple string token associated with its source location context.
 type Identifier struct {
 	node

pkg/pack/ast/source.go

@@ -11,6 +11,6 @@ type Location struct {
 
 // Position consists of a 1-indexed `line` number and a 0-indexed `column` number.
 type Position struct {
-	Line   int64 `json:"line"`   // >= 1
-	Column int64 `json:"column"` // >= 0
+	Line   int64 `json:"line"`   // a 1-based line number
+	Column int64 `json:"column"` // a 0-based column number
 }