fix: panic when head-skipping to a single-byte key

- This was detected by fuzzing! Searching for `{` or `[`
with descendant would cause a panic
if the input started with the sequence
`{"` or `["`, respectively.

Ref: #281

CHANGELOG.md

@@ -2,6 +2,17 @@
 
 All notable changes to this project will be documented in this file.
 
+## [unreleased]
+
+### Bug fixes
+
+- Fixed a bug when head-skipping to a single-byte key would panic.
+  - This was detected by fuzzing!
+  - The queries `$..["{"]` and `$..["["]` would panic
+    on inputs starting with the bytes `{"` or `["`, respectively.
+- Fixed a bug where disabling the `simd` feature would not actually
+  disable SIMD acceleration.
+
 ## [0.8.1] - 2023-09-20
 
 ### Features

Justfile

@@ -233,19 +233,15 @@ commit msg:
 
 # === HOOKS ===
 
-tmpdiff := if os() == "windows" {
-    `New-TemporaryFile`
-} else {
-    `mktemp -t pre-commit-hook-diff-XXXXXXXX.$$`
-}
-
 [private]
-hook-pre-commit: 
+hook-pre-commit:
+    #!/bin/sh
+    tmpdiff=$(mktemp -t pre-commit-hook-diff-XXXXXXXX.$$)
     just assert-benchmarks-committed
-    git diff --full-index --binary > {{tmpdiff}}
+    git diff --full-index --binary > $tmpdiff
     git stash -q --keep-index
     (just verify-fmt && just verify-check); \
-    git apply --whitespace=nowarn < {{tmpdiff}} && git stash drop -q; rm {{tmpdiff}}
+    git apply --whitespace=nowarn < $tmpdiff}} && git stash drop -q; rm $tmpdiff
 
 [private]
 @hook-post-checkout: checkout-benchmarks

crates/rsonpath-lib/src/classification/memmem/nosimd.rs

@@ -58,7 +58,7 @@ where
         while let Some(block) = self.iter.next()? {
             let res = block.iter().copied().enumerate().find(|&(i, c)| {
                 let j = offset + i;
-                c == first_c && self.input.is_member_match(j - 1, j + label_size - 2, label)
+                c == first_c && j > 0 && self.input.is_member_match(j - 1, j + label_size - 2, label)
             });
 
             if let Some((res, _)) = res {

crates/rsonpath-lib/src/classification/memmem/shared/mask_32.rs

@@ -12,7 +12,7 @@ pub(crate) fn find_in_mask<I: Input>(
     let mut result = (previous_block | (first << 1)) & second;
     while result != 0 {
         let idx = result.trailing_zeros() as usize;
-        if input.is_member_match(offset + idx - 2, offset + idx + label_size - 3, label) {
+        if offset + idx > 1 && input.is_member_match(offset + idx - 2, offset + idx + label_size - 3, label) {
             return Some(offset + idx - 2);
         }
         result &= !(1 << idx);

crates/rsonpath-lib/src/classification/memmem/shared/mask_64.rs

@@ -13,7 +13,7 @@ pub(crate) fn find_in_mask<I: Input>(
     while result != 0 {
         let idx = result.trailing_zeros() as usize;
         debug!("{offset} + {idx} - 2 to {offset} + {idx} + {label_size} - 3");
-        if input.is_member_match(offset + idx - 2, offset + idx + label_size - 3, label) {
+        if offset + idx > 1 && input.is_member_match(offset + idx - 2, offset + idx + label_size - 3, label) {
             return Some(offset + idx - 2);
         }
         result &= !(1 << idx);

crates/rsonpath-lib/src/classification/simd.rs

@@ -343,7 +343,13 @@ pub fn configure() -> SimdConfiguration {
     }
 
     cfg_if! {
-        if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+        if #[cfg(not(feature = "simd"))]
+        {
+            let highest_simd = SimdTag::Nosimd;
+            let fast_quotes = false;
+            let fast_popcnt = false;
+        }
+        else if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
         {
             let highest_simd = if is_x86_feature_detected!("avx2") {
                 SimdTag::Avx2

crates/rsonpath-lib/tests/documents/toml/head_skip_for_curly.toml

@@ -0,0 +1,26 @@
+# Define the JSON input for all query test cases.
+[input]
+# Short description of the input structure.
+description = "Object with an empty key."
+ # Set to true only if your specific test input is fully compressed (no extraneous whitespace).
+is_compressed = false
+
+# Inline JSON document.
+[input.source]
+json_string = '{"":null}'
+
+# Define queries to test on the input.
+[[queries]]
+ # Valid JSONPath query string.
+query = '$..["{"]'
+# Short descritpion of the query semantics.
+description = "descendant search for a key equal to the curly brace"
+
+[queries.results]
+# Number of expected matches.
+count = 0
+# Byte locations of spans of all matches, in order.
+spans = []
+# Stringified values of all matches, verbatim as in the input,
+# in the same order as above.
+nodes = []

crates/rsonpath-lib/tests/documents/toml/head_skip_for_square.toml

@@ -0,0 +1,26 @@
+# Define the JSON input for all query test cases.
+[input]
+# Short description of the input structure.
+description = "List with an empty string."
+ # Set to true only if your specific test input is fully compressed (no extraneous whitespace).
+is_compressed = false
+
+# Inline JSON document.
+[input.source]
+json_string = '[""]'
+
+# Define queries to test on the input.
+[[queries]]
+ # Valid JSONPath query string.
+query = '$..["["]'
+# Short descritpion of the query semantics.
+description = "descendant search for a key equal to the square brace"
+
+[queries.results]
+# Number of expected matches.
+count = 0
+# Byte locations of spans of all matches, in order.
+spans = []
+# Stringified values of all matches, verbatim as in the input,
+# in the same order as above.
+nodes = []