From 47218d24f212e7c2842e86977c1e213d65771ec8 Mon Sep 17 00:00:00 2001
From: Dominik Honnef <dominik@honnef.co>
Date: Fri, 25 Mar 2016 06:53:37 +0100
Subject: [PATCH] cmd/guru: whicherrs: don't crash on dead code

Change-Id: I5e80613ec27a4edb45516ff1ff3a88d5f9cb3a67
Reviewed-on: https://go-review.googlesource.com/21130
Reviewed-by: Alan Donovan <adonovan@google.com>
---
 cmd/guru/testdata/src/whicherrs/main.go     | 5 +++++
 cmd/guru/testdata/src/whicherrs/main.golden | 3 +++
 cmd/guru/whicherrs.go                       | 4 ++++
 3 files changed, 12 insertions(+)

diff --git a/cmd/guru/testdata/src/whicherrs/main.go b/cmd/guru/testdata/src/whicherrs/main.go
index 27fe6b56..d1613c58 100644
--- a/cmd/guru/testdata/src/whicherrs/main.go
+++ b/cmd/guru/testdata/src/whicherrs/main.go
@@ -21,6 +21,11 @@ func genErr(i int) error {
 	}
 }
 
+func unreachable() {
+	err := errVar // @whicherrs func-dead "err"
+	_ = err
+}
+
 func main() {
 	err := genErr(0) // @whicherrs localerrs "err"
 	_ = err
diff --git a/cmd/guru/testdata/src/whicherrs/main.golden b/cmd/guru/testdata/src/whicherrs/main.golden
index 1118e0a8..3484752c 100644
--- a/cmd/guru/testdata/src/whicherrs/main.golden
+++ b/cmd/guru/testdata/src/whicherrs/main.golden
@@ -1,3 +1,6 @@
+-------- @whicherrs func-dead --------
+
+Error: pointer analysis did not find expression (dead code?)
 -------- @whicherrs localerrs --------
 this error may point to these globals:
 	errVar
diff --git a/cmd/guru/whicherrs.go b/cmd/guru/whicherrs.go
index 1baf2a47..ff8c1e51 100644
--- a/cmd/guru/whicherrs.go
+++ b/cmd/guru/whicherrs.go
@@ -14,6 +14,7 @@ import (
 	"golang.org/x/tools/cmd/guru/serial"
 	"golang.org/x/tools/go/ast/astutil"
 	"golang.org/x/tools/go/loader"
+	"golang.org/x/tools/go/pointer"
 	"golang.org/x/tools/go/ssa"
 	"golang.org/x/tools/go/ssa/ssautil"
 )
@@ -141,6 +142,9 @@ func whicherrs(q *Query) error {
 
 	ptares := ptrAnalysis(ptaConfig)
 	valueptr := ptares.Queries[value]
+	if valueptr == (pointer.Pointer{}) {
+		return fmt.Errorf("pointer analysis did not find expression (dead code?)")
+	}
 	for g, v := range globals {
 		ptr, ok := ptares.Queries[v]
 		if !ok {