internal/lsp: handle panics due to line numbers in fillstruct

Change-Id: I90f3fd2daf180705048d494476acac5a213f5fb3
Reviewed-on: https://go-review.googlesource.com/c/tools/+/239751
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Baum <joshbaum@google.com>

internal/lsp/analysis/fillstruct/fillstruct.go

@@ -107,7 +107,7 @@ func run(pass *analysis.Pass) (interface{}, error) {
 		case *ast.SelectorExpr:
 			name = fmt.Sprintf("%s.%s", typ.X, typ.Sel.Name)
 		default:
-			log.Printf("anonymous structs are not yet supported: %v (%T)", expr.Type, expr.Type)
+			log.Printf("anonymous structs are not yet supported: (%T)", expr.Type)
 			return
 		}
 
@@ -119,6 +119,7 @@ func run(pass *analysis.Pass) (interface{}, error) {
 		fset := token.NewFileSet()
 		tok := fset.AddFile("", -1, fieldCount+2)
 
+		line := 2 // account for 1-based lines and the left brace
 		var elts []ast.Expr
 		for i := 0; i < fieldCount; i++ {
 			field := obj.Field(i)
@@ -133,8 +134,10 @@ func run(pass *analysis.Pass) (interface{}, error) {
 				continue
 			}
 
-			line := i + 2      // account for 1-based lines and the left brace
-			tok.AddLine(i + 1) // add 1 byte per line
+			tok.AddLine(line - 1) // add 1 byte per line
+			if line > tok.LineCount() {
+				panic(fmt.Sprintf("invalid line number %v (of %v) for fillstruct %s", line, tok.LineCount(), name))
+			}
 			pos := tok.LineStart(line)
 
 			kv := &ast.KeyValueExpr{
@@ -146,6 +149,7 @@ func run(pass *analysis.Pass) (interface{}, error) {
 				Value: value,
 			}
 			elts = append(elts, kv)
+			line++
 		}
 
 		// If all of the struct's fields are unexported, we have nothing to do.
@@ -156,12 +160,16 @@ func run(pass *analysis.Pass) (interface{}, error) {
 		// Add the final line for the right brace. Offset is the number of
 		// bytes already added plus 1.
 		tok.AddLine(len(elts) + 1)
+		line = len(elts) + 2
+		if line > tok.LineCount() {
+			panic(fmt.Sprintf("invalid line number %v (of %v) for fillstruct %s", line, tok.LineCount(), name))
+		}
 
 		cl := &ast.CompositeLit{
 			Type:   expr.Type,
 			Lbrace: tok.LineStart(1),
 			Elts:   elts,
-			Rbrace: tok.LineStart(len(elts) + 2),
+			Rbrace: tok.LineStart(line),
 		}
 
 		// Print the AST to get the the original source code.
@@ -174,13 +182,13 @@ func run(pass *analysis.Pass) (interface{}, error) {
 		// Find the line on which the composite literal is declared.
 		split := strings.Split(b.String(), "\n")
 		lineNumber := pass.Fset.Position(expr.Type.Pos()).Line
-		line := split[lineNumber-1] // lines are 1-indexed
+		firstLine := split[lineNumber-1] // lines are 1-indexed
 
 		// Trim the whitespace from the left of the line, and use the index
 		// to get the amount of whitespace on the left.
-		trimmed := strings.TrimLeftFunc(line, unicode.IsSpace)
-		i := strings.Index(line, trimmed)
-		whitespace := line[:i]
+		trimmed := strings.TrimLeftFunc(firstLine, unicode.IsSpace)
+		index := strings.Index(firstLine, trimmed)
+		whitespace := firstLine[:index]
 
 		var newExpr bytes.Buffer
 		if err := format.Node(&newExpr, fset, cl); err != nil {

internal/lsp/testdata/lsp/primarymod/fillstruct/fill_struct_package.go

@@ -1,9 +1,12 @@
 package fillstruct
 
 import (
+	h2 "net/http"
+
 	"golang.org/x/tools/internal/lsp/fillstruct/data"
 )
 
 func unexported() {
-	a := data.A{} //@suggestedfix("}", "refactor.rewrite")
+	a := data.A{}   //@suggestedfix("}", "refactor.rewrite")
+	_ = h2.Client{} //@suggestedfix("}", "refactor.rewrite")
 }

internal/lsp/testdata/lsp/primarymod/fillstruct/fill_struct_package.go.golden

@@ -1,13 +1,34 @@
--- suggestedfix_fill_struct_package_8_14 --
+-- suggestedfix_fill_struct_package_10_14 --
 package fillstruct
 
 import (
+	h2 "net/http"
+
 	"golang.org/x/tools/internal/lsp/fillstruct/data"
 )
 
 func unexported() {
 	a := data.A{
 		ExportedInt: 0,
+	}   //@suggestedfix("}", "refactor.rewrite")
+	_ = h2.Client{} //@suggestedfix("}", "refactor.rewrite")
+}
+
+-- suggestedfix_fill_struct_package_11_16 --
+package fillstruct
+
+import (
+	h2 "net/http"
+
+	"golang.org/x/tools/internal/lsp/fillstruct/data"
+)
+
+func unexported() {
+	a := data.A{}   //@suggestedfix("}", "refactor.rewrite")
+	_ = h2.Client{
+		Transport: nil,
+		Jar:       nil,
+		Timeout:   0,
 	} //@suggestedfix("}", "refactor.rewrite")
 }
 

internal/lsp/testdata/lsp/summary.txt.golden

@@ -11,7 +11,7 @@ DiagnosticsCount = 44
 FoldingRangesCount = 2
 FormatCount = 6
 ImportCount = 8
-SuggestedFixCount = 13
+SuggestedFixCount = 14
 DefinitionsCount = 53
 TypeDefinitionsCount = 2
 HighlightsCount = 69