internal/lsp: add comment completions for exported vars

This should provide simple name completions for comments
above exported variables.

Can be activated with `ctrl+space` within a comment.

Pretty new, so all help is welcome.

Fixes #34010

Change-Id: I1c8f71baa3beaa22ec5fd9fd4a531284a8d125f3
GitHub-Last-Rev: a9868eb69dc587cb4579268b2c3ae46932702641
GitHub-Pull-Request: golang/tools#166
Reviewed-on: https://go-review.googlesource.com/c/tools/+/197879
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/source/completion.go

@@ -417,12 +417,7 @@ func Completion(ctx context.Context, snapshot Snapshot, f File, pos protocol.Pos
 	if path == nil {
 		return nil, nil, errors.Errorf("cannot find node enclosing position")
 	}
-	// Skip completion inside comments.
-	for _, g := range file.Comments {
-		if g.Pos() <= rng.Start && rng.Start <= g.End() {
-			return nil, nil, nil
-		}
-	}
+
 	// Skip completion inside any kind of literal.
 	if _, ok := path[0].(*ast.BasicLit); ok {
 		return nil, nil, nil
@@ -460,6 +455,14 @@ func Completion(ctx context.Context, snapshot Snapshot, f File, pos protocol.Pos
 
 	c.expectedType = expectedType(c)
 
+	// If we're inside a comment return comment completions
+	for _, comment := range file.Comments {
+		if comment.Pos() <= rng.Start && rng.Start <= comment.End() {
+			c.populateCommentCompletions(comment)
+			return c.items, c.getSurrounding(), nil
+		}
+	}
+
 	// Struct literals are handled entirely separately.
 	if c.wantStructFieldCompletions() {
 		if err := c.structLiteralFieldName(); err != nil {
@@ -534,6 +537,48 @@ func Completion(ctx context.Context, snapshot Snapshot, f File, pos protocol.Pos
 	return c.items, c.getSurrounding(), nil
 }
 
+// populateCommentCompletions returns completions for an exported variable immediately preceeding comment
+func (c *completer) populateCommentCompletions(comment *ast.CommentGroup) {
+
+	// Using the comment position find the line after
+	fset := c.snapshot.View().Session().Cache().FileSet()
+	file := fset.File(comment.Pos())
+	if file == nil {
+		return
+	}
+
+	line := file.Line(comment.Pos())
+	nextLinePos := file.LineStart(line + 1)
+	if !nextLinePos.IsValid() {
+		return
+	}
+
+	// Using the next line pos, grab and parse the exported variable on that line
+	for _, n := range c.file.Decls {
+		if n.Pos() != nextLinePos {
+			continue
+		}
+		switch node := n.(type) {
+		case *ast.GenDecl:
+			if node.Tok != token.VAR {
+				return
+			}
+			for _, spec := range node.Specs {
+				if value, ok := spec.(*ast.ValueSpec); ok {
+					for _, name := range value.Names {
+						if name.Name == "_" || !name.IsExported() {
+							continue
+						}
+
+						exportedVar := c.pkg.GetTypesInfo().ObjectOf(name)
+						c.found(exportedVar, stdScore, nil)
+					}
+				}
+			}
+		}
+	}
+}
+
 func (c *completer) wantStructFieldCompletions() bool {
 	clInfo := c.enclosingCompositeLiteral
 	if clInfo == nil {

internal/lsp/testdata/complit/complit.go.in

@@ -1,12 +1,15 @@
 package complit
 
+// //@complete(" ", cVar)
+var C string //@item(cVar, "C", "string", "var")
+
 type position struct { //@item(structPosition, "position", "struct{...}", "struct")
 	X, Y int //@item(fieldX, "X", "int", "field"),item(fieldY, "Y", "int", "field")
 }
 
 func _() {
 	_ = position{
-		//@complete("", fieldX, fieldY, structPosition)
+		//@complete("", fieldX, fieldY, cVar, structPosition)
 	}
 	_ = position{
 		X: 1,
@@ -18,7 +21,7 @@ func _() {
 	}
 	_ = []*position{
         {
-            //@complete("", fieldX, fieldY, structPosition)
+            //@complete("", fieldX, fieldY, cVar, structPosition)
         },
 	}
 }
@@ -34,7 +37,7 @@ func _() {
 	}
 
 	_ = map[int]int{
-		//@complete("", abVar, aaVar, structPosition)
+		//@complete("", abVar, aaVar, cVar, structPosition)
 	}
 
 	_ = []string{a: ""} //@complete(":", abVar, aaVar)
@@ -42,10 +45,10 @@ func _() {
 
 	_ = position{X: a}   //@complete("}", abVar, aaVar)
 	_ = position{a}      //@complete("}", abVar, aaVar)
-	_ = position{a, }      //@complete("}", abVar, aaVar, structPosition)
+	_ = position{a, }      //@complete("}", abVar, aaVar, cVar, structPosition)
 
-	_ = []int{a}  //@complete("a", abVar, aaVar, structPosition)
-	_ = [1]int{a} //@complete("a", abVar, aaVar, structPosition)
+	_ = []int{a}  //@complete("a", abVar, aaVar, cVar, structPosition)
+	_ = [1]int{a} //@complete("a", abVar, aaVar, cVar, structPosition)
 
 	type myStruct struct {
 		AA int    //@item(fieldAA, "AA", "int", "field")
@@ -70,7 +73,7 @@ func _() {
 
 func _() {
 	_ := position{
-		X: 1, //@complete("X", fieldX),complete(" 1", structPosition)
-		Y: ,  //@complete(":", fieldY),complete(" ,", structPosition)
+		X: 1, //@complete("X", fieldX),complete(" 1", cVar, structPosition)
+		Y: ,  //@complete(":", fieldY),complete(" ,", cVar, structPosition)
 	}
 }

internal/lsp/testdata/summary.txt.golden

@@ -1,5 +1,5 @@
 -- summary --
-CompletionsCount = 219
+CompletionsCount = 220
 CompletionSnippetCount = 51
 UnimportedCompletionsCount = 4
 DeepCompletionsCount = 5