From 70e72abea3267810c19937d83eff69a546d24a68 Mon Sep 17 00:00:00 2001
From: itchyny <itchyny@cybozu.co.jp>
Date: Tue, 18 Feb 2025 07:52:58 +0900
Subject: [PATCH] Fix compiler warning `type-limits` in `found_string` (ref
 #2911) (#3263)

Whether `char` has a sign is implementation dependent, and `c >= 0` may
result in a compiler warning. We can use bitwise operator to check
whether the character is a control character, regardless of the sign.
---
 src/jv_parse.c |  2 +-
 tests/shtest   | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/jv_parse.c b/src/jv_parse.c
index 519c2047..0c50c67c 100644
--- a/src/jv_parse.c
+++ b/src/jv_parse.c
@@ -493,7 +493,7 @@ static pfunc found_string(struct jv_parser* p) {
         return "Invalid escape";
       }
     } else {
-      if (c >= 0 && c <= 0x001f)
+      if (!(c & ~0x1F))
         return "Invalid string: control characters from U+0000 through U+001F must be escaped";
       *out++ = c;
     }
diff --git a/tests/shtest b/tests/shtest
index 7a482e51..efb63771 100755
--- a/tests/shtest
+++ b/tests/shtest
@@ -94,6 +94,20 @@ if printf '1\n' | $JQ -cen --seq '[inputs] == []' >/dev/null 2> $d/out; then
 fi
 cmp $d/out $d/expected
 
+# Test control characters for #2909
+cat > $d/expected <<EOF
+jq: parse error: Invalid string: control characters from U+0000 through U+001F must be escaped at line 1, column 3
+EOF
+for i in 1 2 30 31; do
+  if printf "\"$(printf '\\%03o' $i)\"" | $JQ '.' > $d/out 2>&1; then
+    printf 'Error expected but jq exited successfully\n' 1>&2
+    exit 2
+  fi
+  cmp $d/out $d/expected
+done
+printf '" ~\\u007f"\n' > $d/expected
+printf "\"$(printf '\\%03o' 32 126 127)\"" | $JQ '.' > $d/out 2>&1
+cmp $d/out $d/expected
 
 ## Test --exit-status
 data='{"i": 1}\n{"i": 2}\n{"i": 3}\n'