Joseph Tsai (Gerrit)

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Jul 31, 2025, 7:24:46 PMJul 31

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Joseph Tsai has uploaded the change for review

Commit message

encoding/json: fix Indent trailing whitespace regression in goexperiment.jsonv2

The Indent function preserves trailing whitespace,
while the v1 emulation under v2 implementation accidentally dropped it.

There was prior logic that attempted to preserve it,
but it did not work correctly since it ran in a defer and
accidentally mutated the dst input argument rather than the output argument.
Move the logic to the end and avoid a defer.
Also, add a test to both v1 and v1in2 to codify this behavior.

This only modifies code that is compiled in under goexperiment.jsonv2.

Updates #13520
Fixes #74806

Change-Id: I22b1a8da5185eb969e2a8a111b625d3752cfcbe8

Change diff

diff --git a/src/encoding/json/scanner_test.go b/src/encoding/json/scanner_test.go
index fb64463..a062e91 100644
--- a/src/encoding/json/scanner_test.go
+++ b/src/encoding/json/scanner_test.go
@@ -74,6 +74,7 @@
 	-5e+2
 ]`},
 		{Name(""), "{\"\":\"<>&\u2028\u2029\"}", "{\n\t\"\": \"<>&\u2028\u2029\"\n}"}, // See golang.org/issue/34070
+		{Name(""), `null`, "null \n\r\t"},                                             // See golang.org/issue/13520 and golang.org/issue/74806
 	}
 	var buf bytes.Buffer
 	for _, tt := range tests {
@@ -102,7 +103,7 @@
 			buf.Reset()
 			if err := Indent(&buf, []byte(tt.compact), "", "\t"); err != nil {
 				t.Errorf("%s: Indent error: %v", tt.Where, err)
-			} else if got := buf.String(); got != tt.indent {
+			} else if got := buf.String(); got != strings.TrimRight(tt.indent, " \n\r\t") {
 				t.Errorf("%s: Compact:\n\tgot:  %s\n\twant: %s", tt.Where, indentNewlines(got), indentNewlines(tt.indent))
 			}
 		})
diff --git a/src/encoding/json/v2_indent.go b/src/encoding/json/v2_indent.go
index 2655942..b2e8518 100644
--- a/src/encoding/json/v2_indent.go
+++ b/src/encoding/json/v2_indent.go
@@ -88,17 +88,8 @@
 }
 
 func appendIndent(dst, src []byte, prefix, indent string) ([]byte, error) {
-	// In v2, trailing whitespace is discarded, while v1 preserved it.
-	dstLen := len(dst)
-	if n := len(src) - len(bytes.TrimRight(src, " \n\r\t")); n > 0 {
-		// Append the trailing whitespace afterwards.
-		defer func() {
-			if len(dst) > dstLen {
-				dst = append(dst, src[len(src)-n:]...)
-			}
-		}()
-	}
 	// In v2, only spaces and tabs are allowed, while v1 allowed any character.
+	dstLen := len(dst)
 	if len(strings.Trim(prefix, " \t"))+len(strings.Trim(indent, " \t")) > 0 {
 		// Use placeholder spaces of correct length, and replace afterwards.
 		invalidPrefix, invalidIndent := prefix, indent
@@ -129,5 +120,10 @@
 	if err != nil {
 		return dst[:dstLen], transformSyntacticError(err)
 	}
+
+	// In v2, trailing whitespace is discarded, while v1 preserved it.
+	if n := len(src) - len(bytes.TrimRight(src, " \n\r\t")); n > 0 {
+		dst = append(dst, src[len(src)-n:]...)
+	}
 	return dst, nil
 }
diff --git a/src/encoding/json/v2_scanner_test.go b/src/encoding/json/v2_scanner_test.go
index bec5521..8885520 100644
--- a/src/encoding/json/v2_scanner_test.go
+++ b/src/encoding/json/v2_scanner_test.go
@@ -74,6 +74,7 @@
 	-5e+2
 ]`},
 		{Name(""), "{\"\":\"<>&\u2028\u2029\"}", "{\n\t\"\": \"<>&\u2028\u2029\"\n}"}, // See golang.org/issue/34070
+		{Name(""), `null`, "null \n\r\t"},                                             // See golang.org/issue/13520 and golang.org/issue/74806
 	}
 	var buf bytes.Buffer
 	for _, tt := range tests {
@@ -102,7 +103,7 @@
 			buf.Reset()
 			if err := Indent(&buf, []byte(tt.compact), "", "\t"); err != nil {
 				t.Errorf("%s: Indent error: %v", tt.Where, err)
-			} else if got := buf.String(); got != tt.indent {
+			} else if got := buf.String(); got != strings.TrimRight(tt.indent, " \n\r\t") {
 				t.Errorf("%s: Compact:\n\tgot:  %s\n\twant: %s", tt.Where, indentNewlines(got), indentNewlines(tt.indent))
 			}
 		})

Change information

Files:

M src/encoding/json/scanner_test.go
M src/encoding/json/v2_indent.go
M src/encoding/json/v2_scanner_test.go

Change size: S

Delta: 3 files changed, 10 insertions(+), 12 deletions(-)

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Joseph Tsai (Gerrit)

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Change information

Commit message:

encoding/json: fix Indent trailing whitespace regression in goexperiment.jsonv2

The Indent function preserves trailing whitespace,
while the v1 emulation under v2 implementation accidentally dropped it.

There was prior logic that attempted to preserve it,
but it did not work correctly since it ran in a defer and
accidentally mutated the dst input argument rather than the output argument.
Move the logic to the end and avoid a defer.
Also, add a test to both v1 and v1in2 to codify this behavior.

This only modifies code that is compiled in under goexperiment.jsonv2.

Updates #13520
Fixes #74806

Change-Id: I22b1a8da5185eb969e2a8a111b625d3752cfcbe8

Reviewed-on: https://go-review.googlesource.com/c/go/+/692195

Reviewed-by: Sean Liao <se...@liao.dev>

LUCI-TryBot-Result: Go LUCI <golang...@luci-project-accounts.iam.gserviceaccount.com>

Reviewed-by: Dmitri Shuralyov <dmit...@google.com>

Reviewed-by: David Chase <drc...@google.com>

Auto-Submit: Sean Liao <se...@liao.dev>

Files:

M src/encoding/json/scanner_test.go
M src/encoding/json/v2_indent.go
M src/encoding/json/v2_scanner_test.go

Change size: S

Delta: 3 files changed, 10 insertions(+), 12 deletions(-)

Branch: refs/heads/master

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[go] encoding/json: fix Indent trailing whitespace regression in goexperiment.jsonv2

Joseph Tsai (Gerrit)

Joseph Tsai has uploaded the change for review

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Joseph Tsai (Gerrit)

Joseph Tsai voted

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Sean Liao (Gerrit)

Sean Liao voted

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Dmitri Shuralyov (Gerrit)

Dmitri Shuralyov voted Code-Review+1

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David Chase (Gerrit)

David Chase voted Code-Review+1

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Gopher Robot (Gerrit)

Gopher Robot submitted the change

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