go/analysis: add an End field to Diagnostic

This will allow diagnostics to denote the range they apply to.
The ranges are now interpreted using the internal/span library.

This is primarily intended for the benefit of the LSP, which will
be able to (in future CLs) more accurately highlight the part
of the code a diagnostic applies to.

Change-Id: Ic35cec2b21060c9dc6a8f5ebb7faa62d81a07435
Reviewed-on: https://go-review.googlesource.com/c/tools/+/179237
Run-TryBot: Michael Matloob <matloob@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>

go/analysis/analysis.go

@@ -161,6 +161,15 @@ func (pass *Pass) Reportf(pos token.Pos, format string, args ...interface{}) {
 	pass.Report(Diagnostic{Pos: pos, Message: msg})
 }
 
+// reportNodef is a helper function that reports a Diagnostic using the
+// range denoted by the AST node.
+//
+// WARNING: This is an experimental API and may change in the future.
+func (pass *Pass) reportNodef(node ast.Node, format string, args ...interface{}) {
+	msg := fmt.Sprintf(format, args...)
+	pass.Report(Diagnostic{Pos: node.Pos(), End: node.End(), Message: msg})
+}
+
 func (pass *Pass) String() string {
 	return fmt.Sprintf("%s@%s", pass.Analyzer.Name, pass.Pkg.Path())
 }
@@ -203,13 +212,17 @@ type Fact interface {
 	AFact() // dummy method to avoid type errors
 }
 
-// A Diagnostic is a message associated with a source location.
+// A Diagnostic is a message associated with a source location or range.
 //
 // An Analyzer may return a variety of diagnostics; the optional Category,
 // which should be a constant, may be used to classify them.
 // It is primarily intended to make it easy to look up documentation.
+//
+// If End is provided, the diagnostic is specified to apply to the range between
+// Pos and End.
 type Diagnostic struct {
 	Pos      token.Pos
+	End      token.Pos // optional
 	Category string    // optional
 	Message  string
 }

go/analysis/analysistest/analysistest.go

@@ -257,6 +257,7 @@ func check(t Testing, gopath string, pass *analysis.Pass, diagnostics []analysis
 
 	// Check the diagnostics match expectations.
 	for _, f := range diagnostics {
+		// TODO(matloob): Support ranges in analysistest.
 		posn := pass.Fset.Position(f.Pos)
 		checkMessage(posn, "diagnostic", "", f.Message)
 	}

go/analysis/internal/analysisflags/flags.go

@@ -323,9 +323,14 @@ func PrintPlain(fset *token.FileSet, diag analysis.Diagnostic) {
 
 	// -c=N: show offending line plus N lines of context.
 	if Context >= 0 {
+		posn := fset.Position(diag.Pos)
+		end := fset.Position(diag.End)
+		if !end.IsValid() {
+			end = posn
+		}
 		data, _ := ioutil.ReadFile(posn.Filename)
 		lines := strings.Split(string(data), "\n")
-		for i := posn.Line - Context; i <= posn.Line+Context; i++ {
+		for i := posn.Line - Context; i <= end.Line+Context; i++ {
 			if 1 <= i && i <= len(lines) {
 				fmt.Fprintf(os.Stderr, "%d\t%s\n", i, lines[i-1])
 			}
@@ -353,6 +358,8 @@ func (tree JSONTree) Add(fset *token.FileSet, id, name string, diags []analysis.
 			Message  string `json:"message"`
 		}
 		var diagnostics []jsonDiagnostic
+		// TODO(matloob): Should the JSON diagnostics contain ranges?
+		// If so, how should they be formatted?
 		for _, f := range diags {
 			diagnostics = append(diagnostics, jsonDiagnostic{
 				Category: f.Category,

go/analysis/internal/checker/checker.go

@@ -295,7 +295,8 @@ func printDiagnostics(roots []*action) (exitcode int) {
 		// avoid double-reporting in source files that belong to
 		// multiple packages, such as foo and foo.test.
 		type key struct {
-			token.Position
+			pos token.Position
+			end token.Position
 			*analysis.Analyzer
 			message string
 		}
@@ -313,7 +314,8 @@ func printDiagnostics(roots []*action) (exitcode int) {
 					// as most users don't care.
 
 					posn := act.pkg.Fset.Position(diag.Pos)
-					k := key{posn, act.a, diag.Message}
+					end := act.pkg.Fset.Position(diag.End)
+					k := key{posn, end, act.a, diag.Message}
 					if seen[k] {
 						continue // duplicate
 					}

internal/lsp/source/diagnostics.go

@@ -133,7 +133,7 @@ func diagnostics(ctx context.Context, v View, pkg Package, reports map[span.URI]
 func analyses(ctx context.Context, v View, pkg Package, reports map[span.URI][]Diagnostic) error {
 	// Type checking and parsing succeeded. Run analyses.
 	if err := runAnalyses(ctx, v, pkg, func(a *analysis.Analyzer, diag analysis.Diagnostic) error {
-		r := span.NewRange(v.Session().Cache().FileSet(), diag.Pos, 0)
+		r := span.NewRange(v.Session().Cache().FileSet(), diag.Pos, diag.End)
 		s, err := r.Span()
 		if err != nil {
 			// The diagnostic has an invalid position, so we don't have a valid span.