From 596a8c33492d713c4ae4b20ecf83f41cf049e978 Mon Sep 17 00:00:00 2001
From: haoqixu <hq.xu0o0@gmail.com>
Date: Thu, 8 Aug 2024 19:35:45 +0800
Subject: [PATCH] encoding/json: fix location for JSON syntax error
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The JSON decoder utilizes `parser.ParseExpr` to parse input data,
which could be a valid CUE expression but an invalid JSON.

Using the error position returned by `parser.ParseExpr` as output
may cause cue to either omit the position or report the wrong position

This change uses the offset returned by the JSON parser and
recalculate the position to ensure the reported position is accurate.

Fixes #3317

Change-Id: I019ab80c275d658f5773501d766ee9d03261ab58
Signed-off-by: haoqixu <hq.xu0o0@gmail.com>
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1199094
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
---
 .../testdata/script/json_syntax_error.txtar   | 26 +++++++++++++++++++
 encoding/json/json.go                         | 10 +++++++
 2 files changed, 36 insertions(+)
 create mode 100644 cmd/cue/cmd/testdata/script/json_syntax_error.txtar

diff --git a/cmd/cue/cmd/testdata/script/json_syntax_error.txtar b/cmd/cue/cmd/testdata/script/json_syntax_error.txtar
new file mode 100644
index 00000000000..6d40a57a8ce
--- /dev/null
+++ b/cmd/cue/cmd/testdata/script/json_syntax_error.txtar
@@ -0,0 +1,26 @@
+! exec cue export x1.json
+stderr 'x1*.json:4:3'
+
+! exec cue export x2.json
+stderr 'x2.json:1:6'
+
+! exec cue export x3.json
+stderr 'x3.json:1:1'
+
+! exec cue export x4.json
+stderr 'x4.json:1:1'
+
+-- x1.json --
+{
+  "foo": true,
+  "bar": 2
+  "baz": false
+}
+
+-- x2.json --
+"baz": false
+
+-- x3.json --
+baz: false
+
+-- x4.json --
diff --git a/encoding/json/json.go b/encoding/json/json.go
index aaff32506d6..b21828ebce8 100644
--- a/encoding/json/json.go
+++ b/encoding/json/json.go
@@ -87,6 +87,16 @@ func extract(path string, b []byte) (ast.Expr, error) {
 		}
 		var x interface{}
 		err := json.Unmarshal(b, &x)
+
+		if len(b) > 0 {
+			var synErr *json.SyntaxError
+			if errors.As(err, &synErr) {
+				tokFile := token.NewFile(path, 0, len(b))
+				tokFile.SetLinesForContent(b)
+				p = tokFile.Pos(int(synErr.Offset-1), token.NoRelPos)
+			}
+		}
+
 		return nil, errors.Wrapf(err, p, "invalid JSON for file %q", path)
 	}
 	return expr, nil