diff --git a/internal/lsp/cache/errors.go b/internal/lsp/cache/errors.go
index ffc236d26c..10f7d1f014 100644
--- a/internal/lsp/cache/errors.go
+++ b/internal/lsp/cache/errors.go
@@ -22,6 +22,7 @@ import (
 	"golang.org/x/tools/internal/lsp/protocol"
 	"golang.org/x/tools/internal/lsp/source"
 	"golang.org/x/tools/internal/span"
+	"golang.org/x/tools/internal/typesinternal"
 	errors "golang.org/x/xerrors"
 )
 
@@ -31,6 +32,7 @@ func sourceError(ctx context.Context, snapshot *snapshot, pkg *pkg, e interface{
 		spn           span.Span
 		err           error
 		msg, category string
+		code          typesinternal.ErrorCode
 		kind          source.ErrorKind
 		fixes         []source.SuggestedFix
 		related       []source.RelatedInformation
@@ -90,7 +92,7 @@ func sourceError(ctx context.Context, snapshot *snapshot, pkg *pkg, e interface{
 		if !e.Pos.IsValid() {
 			return nil, fmt.Errorf("invalid position for type error %v", e)
 		}
-		spn, err = typeErrorRange(snapshot, fset, pkg, e.Pos)
+		code, spn, err = typeErrorData(fset, pkg, e)
 		if err != nil {
 			return nil, err
 		}
@@ -101,14 +103,14 @@ func sourceError(ctx context.Context, snapshot *snapshot, pkg *pkg, e interface{
 		if !perr.Pos.IsValid() {
 			return nil, fmt.Errorf("invalid position for type error %v", e)
 		}
-		spn, err = typeErrorRange(snapshot, fset, pkg, perr.Pos)
+		code, spn, err = typeErrorData(fset, pkg, e.primary)
 		if err != nil {
 			return nil, err
 		}
 		for _, s := range e.secondaries {
 			var x source.RelatedInformation
 			x.Message = s.Msg
-			xspn, err := typeErrorRange(snapshot, fset, pkg, s.Pos)
+			_, xspn, err := typeErrorData(fset, pkg, s)
 			if err != nil {
 				return nil, fmt.Errorf("invalid position for type error %v", s)
 			}
@@ -143,7 +145,7 @@ func sourceError(ctx context.Context, snapshot *snapshot, pkg *pkg, e interface{
 	if err != nil {
 		return nil, err
 	}
-	return &source.Error{
+	se := &source.Error{
 		URI:            spn.URI(),
 		Range:          rng,
 		Message:        msg,
@@ -151,7 +153,17 @@ func sourceError(ctx context.Context, snapshot *snapshot, pkg *pkg, e interface{
 		Category:       category,
 		SuggestedFixes: fixes,
 		Related:        related,
-	}, nil
+	}
+	if code != 0 {
+		se.Code = code.String()
+		se.CodeHref = typesCodeHref(snapshot, code)
+	}
+	return se, nil
+}
+
+func typesCodeHref(snapshot *snapshot, code typesinternal.ErrorCode) string {
+	target := snapshot.View().Options().LinkTarget
+	return fmt.Sprintf("%s/golang.org/x/tools/internal/typesinternal#%s", target, code.String())
 }
 
 func suggestedAnalysisFixes(snapshot *snapshot, pkg *pkg, diag *analysis.Diagnostic) ([]source.SuggestedFix, error) {
@@ -213,18 +225,29 @@ func toSourceErrorKind(kind packages.ErrorKind) source.ErrorKind {
 	}
 }
 
-func typeErrorRange(snapshot *snapshot, fset *token.FileSet, pkg *pkg, pos token.Pos) (span.Span, error) {
-	posn := fset.Position(pos)
+func typeErrorData(fset *token.FileSet, pkg *pkg, terr types.Error) (typesinternal.ErrorCode, span.Span, error) {
+	ecode, start, end, ok := typesinternal.ReadGo116ErrorData(terr)
+	if !ok {
+		start, end = terr.Pos, terr.Pos
+		ecode = 0
+	}
+	posn := fset.Position(start)
 	pgf, err := pkg.File(span.URIFromPath(posn.Filename))
 	if err != nil {
-		return span.Span{}, err
+		return 0, span.Span{}, err
 	}
-	return span.Range{
-		FileSet:   fset,
-		Start:     pos,
-		End:       analysisinternal.TypeErrorEndPos(fset, pgf.Src, pos),
-		Converter: pgf.Mapper.Converter,
-	}.Span()
+	if !end.IsValid() || end == start {
+		end = analysisinternal.TypeErrorEndPos(fset, pgf.Src, start)
+	}
+	spn, err := parsedGoSpan(pgf, start, end)
+	if err != nil {
+		return 0, span.Span{}, err
+	}
+	return ecode, spn, nil
+}
+
+func parsedGoSpan(pgf *source.ParsedGoFile, start, end token.Pos) (span.Span, error) {
+	return span.FileSpan(pgf.Tok, pgf.Mapper.Converter, start, end)
 }
 
 func scannerErrorRange(snapshot *snapshot, pkg *pkg, posn token.Position) (span.Span, error) {
diff --git a/internal/lsp/diagnostics.go b/internal/lsp/diagnostics.go
index 3b1ab9b011..7e6acb123e 100644
--- a/internal/lsp/diagnostics.go
+++ b/internal/lsp/diagnostics.go
@@ -445,6 +445,8 @@ func (s *Server) storeErrorDiagnostics(ctx context.Context, snapshot source.Snap
 			Related:  e.Related,
 			Severity: protocol.SeverityError,
 			Source:   e.Category,
+			Code:     e.Code,
+			CodeHref: e.CodeHref,
 		}
 		s.storeDiagnostics(snapshot, e.URI, dsource, []*source.Diagnostic{diagnostic})
 	}
@@ -534,7 +536,7 @@ func toProtocolDiagnostics(diagnostics []*source.Diagnostic) []protocol.Diagnost
 				Message: rel.Message,
 			})
 		}
-		reports = append(reports, protocol.Diagnostic{
+		pdiag := protocol.Diagnostic{
 			// diag.Message might start with \n or \t
 			Message:            strings.TrimSpace(diag.Message),
 			Range:              diag.Range,
@@ -542,7 +544,14 @@ func toProtocolDiagnostics(diagnostics []*source.Diagnostic) []protocol.Diagnost
 			Source:             diag.Source,
 			Tags:               diag.Tags,
 			RelatedInformation: related,
-		})
+		}
+		if diag.Code != "" {
+			pdiag.Code = diag.Code
+		}
+		if diag.CodeHref != "" {
+			pdiag.CodeDescription = &protocol.CodeDescription{Href: diag.CodeHref}
+		}
+		reports = append(reports, pdiag)
 	}
 	return reports
 }
diff --git a/internal/lsp/source/diagnostics.go b/internal/lsp/source/diagnostics.go
index a9bffbdb9e..1dd937a543 100644
--- a/internal/lsp/source/diagnostics.go
+++ b/internal/lsp/source/diagnostics.go
@@ -18,6 +18,8 @@ type Diagnostic struct {
 	Range    protocol.Range
 	Message  string
 	Source   string
+	Code     string
+	CodeHref string
 	Severity protocol.DiagnosticSeverity
 	Tags     []protocol.DiagnosticTag
 
diff --git a/internal/lsp/source/view.go b/internal/lsp/source/view.go
index 8b7673d9d5..ff9dade5fc 100644
--- a/internal/lsp/source/view.go
+++ b/internal/lsp/source/view.go
@@ -579,7 +579,11 @@ type Error struct {
 	Kind     ErrorKind
 	Message  string
 	Category string // only used by analysis errors so far
-	Related  []RelatedInformation
+
+	Related []RelatedInformation
+
+	Code     string
+	CodeHref string
 
 	// SuggestedFixes is used to generate quick fixes for a CodeAction request.
 	// It isn't part of the Diagnostic type.
diff --git a/internal/lsp/testdata/bad/bad0.go b/internal/lsp/testdata/bad/bad0.go
index cfde87c87c..36a4e6b95f 100644
--- a/internal/lsp/testdata/bad/bad0.go
+++ b/internal/lsp/testdata/bad/bad0.go
@@ -18,6 +18,6 @@ type bob struct { //@item(bob, "bob", "struct{...}", "struct")
 func _() {
 	var q int
 	_ = &bob{
-		f: q, //@diag("f", "compiler", "unknown field f in struct literal", "error")
+		f: q, //@diag("f: q", "compiler", "unknown field f in struct literal", "error")
 	}
 }
diff --git a/internal/lsp/tests/util.go b/internal/lsp/tests/util.go
index 9fed4deb77..b46f15980e 100644
--- a/internal/lsp/tests/util.go
+++ b/internal/lsp/tests/util.go
@@ -129,18 +129,34 @@ func DiffDiagnostics(uri span.URI, want, got []*source.Diagnostic) string {
 		if w.Source != g.Source {
 			return summarizeDiagnostics(i, uri, want, got, "incorrect Source got %v want %v", g.Source, w.Source)
 		}
-		if protocol.ComparePosition(w.Range.Start, g.Range.Start) != 0 {
-			return summarizeDiagnostics(i, uri, want, got, "incorrect Start got %v want %v", g.Range.Start, w.Range.Start)
-		}
-		if !protocol.IsPoint(g.Range) { // Accept any 'want' range if the diagnostic returns a zero-length range.
-			if protocol.ComparePosition(w.Range.End, g.Range.End) != 0 {
-				return summarizeDiagnostics(i, uri, want, got, "incorrect End got %v want %v", g.Range.End, w.Range.End)
-			}
+		if !rangeOverlaps(g.Range, w.Range) {
+			return summarizeDiagnostics(i, uri, want, got, "range %v does not overlap %v", g.Range, w.Range)
 		}
 	}
 	return ""
 }
 
+// rangeOverlaps reports whether r1 and r2 overlap.
+func rangeOverlaps(r1, r2 protocol.Range) bool {
+	if inRange(r2.Start, r1) || inRange(r1.Start, r2) {
+		return true
+	}
+	return false
+}
+
+// inRange reports whether p is contained within [r.Start, r.End), or if p ==
+// r.Start == r.End (special handling for the case where the range is a single
+// point).
+func inRange(p protocol.Position, r protocol.Range) bool {
+	if protocol.IsPoint(r) {
+		return protocol.ComparePosition(r.Start, p) == 0
+	}
+	if protocol.ComparePosition(r.Start, p) <= 0 && protocol.ComparePosition(p, r.End) < 0 {
+		return true
+	}
+	return false
+}
+
 func summarizeDiagnostics(i int, uri span.URI, want, got []*source.Diagnostic, reason string, args ...interface{}) string {
 	msg := &bytes.Buffer{}
 	fmt.Fprint(msg, "diagnostics failed")
diff --git a/internal/span/token.go b/internal/span/token.go
index 10b429efd1..6f8b9b570c 100644
--- a/internal/span/token.go
+++ b/internal/span/token.go
@@ -19,12 +19,16 @@ type Range struct {
 	Converter Converter
 }
 
+type FileConverter struct {
+	file *token.File
+}
+
 // TokenConverter is a Converter backed by a token file set and file.
 // It uses the file set methods to work out the conversions, which
 // makes it fast and does not require the file contents.
 type TokenConverter struct {
+	FileConverter
 	fset *token.FileSet
-	file *token.File
 }
 
 // NewRange creates a new Range from a FileSet and two positions.
@@ -40,7 +44,7 @@ func NewRange(fset *token.FileSet, start, end token.Pos) Range {
 // NewTokenConverter returns an implementation of Converter backed by a
 // token.File.
 func NewTokenConverter(fset *token.FileSet, f *token.File) *TokenConverter {
-	return &TokenConverter{fset: fset, file: f}
+	return &TokenConverter{fset: fset, FileConverter: FileConverter{file: f}}
 }
 
 // NewContentConverter returns an implementation of Converter for the
@@ -49,7 +53,7 @@ func NewContentConverter(filename string, content []byte) *TokenConverter {
 	fset := token.NewFileSet()
 	f := fset.AddFile(filename, -1, len(content))
 	f.SetLinesForContent(content)
-	return &TokenConverter{fset: fset, file: f}
+	return NewTokenConverter(fset, f)
 }
 
 // IsPoint returns true if the range represents a single point.
@@ -68,17 +72,23 @@ func (r Range) Span() (Span, error) {
 	if f == nil {
 		return Span{}, fmt.Errorf("file not found in FileSet")
 	}
+	return FileSpan(f, r.Converter, r.Start, r.End)
+}
+
+// FileSpan returns a span within tok, using converter to translate between
+// offsets and positions.
+func FileSpan(tok *token.File, converter Converter, start, end token.Pos) (Span, error) {
 	var s Span
 	var err error
 	var startFilename string
-	startFilename, s.v.Start.Line, s.v.Start.Column, err = position(f, r.Start)
+	startFilename, s.v.Start.Line, s.v.Start.Column, err = position(tok, start)
 	if err != nil {
 		return Span{}, err
 	}
 	s.v.URI = URIFromPath(startFilename)
-	if r.End.IsValid() {
+	if end.IsValid() {
 		var endFilename string
-		endFilename, s.v.End.Line, s.v.End.Column, err = position(f, r.End)
+		endFilename, s.v.End.Line, s.v.End.Column, err = position(tok, end)
 		if err != nil {
 			return Span{}, err
 		}
@@ -91,13 +101,13 @@ func (r Range) Span() (Span, error) {
 	s.v.Start.clean()
 	s.v.End.clean()
 	s.v.clean()
-	if r.Converter != nil {
-		return s.WithOffset(r.Converter)
+	if converter != nil {
+		return s.WithOffset(converter)
 	}
-	if startFilename != f.Name() {
-		return Span{}, fmt.Errorf("must supply Converter for file %q containing lines from %q", f.Name(), startFilename)
+	if startFilename != tok.Name() {
+		return Span{}, fmt.Errorf("must supply Converter for file %q containing lines from %q", tok.Name(), startFilename)
 	}
-	return s.WithOffset(NewTokenConverter(r.FileSet, f))
+	return s.WithOffset(&FileConverter{tok})
 }
 
 func position(f *token.File, pos token.Pos) (string, int, int, error) {
@@ -154,12 +164,12 @@ func (s Span) Range(converter *TokenConverter) (Range, error) {
 	}, nil
 }
 
-func (l *TokenConverter) ToPosition(offset int) (int, int, error) {
+func (l *FileConverter) ToPosition(offset int) (int, int, error) {
 	_, line, col, err := positionFromOffset(l.file, offset)
 	return line, col, err
 }
 
-func (l *TokenConverter) ToOffset(line, col int) (int, error) {
+func (l *FileConverter) ToOffset(line, col int) (int, error) {
 	if line < 0 {
 		return -1, fmt.Errorf("line is not valid")
 	}
diff --git a/internal/typesinternal/types.go b/internal/typesinternal/types.go
index a5bb408e2f..c3e1a397db 100644
--- a/internal/typesinternal/types.go
+++ b/internal/typesinternal/types.go
@@ -2,9 +2,12 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Package typesinternal provides access to internal go/types APIs that are not
+// yet exported.
 package typesinternal
 
 import (
+	"go/token"
 	"go/types"
 	"reflect"
 	"unsafe"
@@ -26,3 +29,17 @@ func SetUsesCgo(conf *types.Config) bool {
 
 	return true
 }
+
+func ReadGo116ErrorData(terr types.Error) (ErrorCode, token.Pos, token.Pos, bool) {
+	var data [3]int
+	// By coincidence all of these fields are ints, which simplifies things.
+	v := reflect.ValueOf(terr)
+	for i, name := range []string{"go116code", "go116start", "go116end"} {
+		f := v.FieldByName(name)
+		if !f.IsValid() {
+			return 0, 0, 0, false
+		}
+		data[i] = int(f.Int())
+	}
+	return ErrorCode(data[0]), token.Pos(data[1]), token.Pos(data[2]), true
+}