From: Samuel Tan <samueltan@gmail.com>
Date: Tue, 11 Jun 2019 05:18:56 +0000 (-0700)
Subject: html/template: handle nil Error values in context.String
X-Git-Tag: go1.13beta1~65
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=db042d2d42e1009bb9d6c12a7a018108638e1dae;p=gostls13.git

html/template: handle nil Error values in context.String

Add a special case to print a generic nil error when context.err is
nil.

Previously, this case was unchecked, leading to a call to (*Error).Error
with a nil receiver, which was triggering a nil pointer access. However,
this bug was masked by the panic-recovery code in package fmt.

I tested this change by running `dlv test` in src/html/template, running
the `continue` command, and verifying that no "bad access" errors are
returned.

Fixes #28854

Change-Id: I0b637b943de003d9efc294f6f1e49b793668d037
Reviewed-on: https://go-review.googlesource.com/c/go/+/181579
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
---

diff --git a/src/html/template/context.go b/src/html/template/context.go
index 7ab3d1fed6..f7d4849928 100644
--- a/src/html/template/context.go
+++ b/src/html/template/context.go
@@ -26,7 +26,11 @@ type context struct {
 }
 
 func (c context) String() string {
-	return fmt.Sprintf("{%v %v %v %v %v %v %v}", c.state, c.delim, c.urlPart, c.jsCtx, c.attr, c.element, c.err)
+	var err error
+	if c.err != nil {
+		err = c.err
+	}
+	return fmt.Sprintf("{%v %v %v %v %v %v %v}", c.state, c.delim, c.urlPart, c.jsCtx, c.attr, c.element, err)
 }
 
 // eq reports whether two contexts are equal.