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Fix OOB errors in the lexer #8734

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Merged
tlively merged 1 commit into from
May 20, 2026
+18 −1
Merged

Fix OOB errors in the lexer #8734

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10 changes: 9 additions & 1 deletion src/parser/lexer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -624,6 +624,9 @@ inline std::optional<uint64_t> Lexer::takeHexnum(OverflowBehavior behavior) {
}

inline Lexer::Sign Lexer::takeSign() {
if (empty()) {
return NoSign;
}
auto c = peek();
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@stevenfontanella stevenfontanella May 20, 2026

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Should we make peek return optional so that future callers know to check if they hit the end of the buffer?

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@tlively tlively May 20, 2026

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Sure, I did that in #8737 as a follow-up because the diff for that change swamps the diff for fixing these bugs.

if (c == '+') {
take(1);
Expand Down Expand Up @@ -812,7 +815,8 @@ inline std::optional<Lexer::LexedFloat> Lexer::takeFloat() {
// we need to strip any underscores since `std::strtod` does not understand
// them.
std::stringstream ss;
for (const char *curr = &buffer[startPos], *end = &buffer[pos]; curr != end;
for (const char *curr = buffer.data() + startPos, *end = buffer.data() + pos;
curr != end;
++curr) {
if (*curr != '_') {
ss << *curr;
Expand Down Expand Up @@ -853,6 +857,10 @@ inline std::optional<Lexer::StringOrView> Lexer::takeStr() {
// Escape sequences
ensureBuildingEscaped();
take(1);
if (empty()) {
pos = startPos;
return std::nullopt;
}
auto c = peek();
take(1);
switch (c) {
Expand Down
9 changes: 9 additions & 0 deletions test/gtest/wat-lexer.cpp
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Expand Up @@ -22,6 +22,14 @@
using namespace wasm::WATParser;
using namespace std::string_view_literals;

TEST(LexerTest, EmptyInput) {
EXPECT_TRUE(Lexer(""sv).empty());
EXPECT_EQ(Lexer(""sv).takeI32(), std::nullopt);
EXPECT_EQ(Lexer(""sv).takeF32(), std::nullopt);
EXPECT_EQ(Lexer(""sv).takeString(), std::nullopt);
EXPECT_EQ(Lexer(""sv).takeID(), std::nullopt);
}

TEST(LexerTest, LexWhitespace) {
Lexer lexer(" 1\t2\n3\r4 \n\n\t 5 "sv);

Expand Down Expand Up @@ -915,6 +923,7 @@ TEST(LexerTest, LexString) {
"_$_\xC2\xA3_\xE2\x82\xAC_\xF0\x90\x8D\x88_"s);

EXPECT_FALSE(Lexer("\"unterminated"sv).takeString());
EXPECT_FALSE(Lexer("\"foo\\"sv).takeString());
EXPECT_FALSE(Lexer("\"unescaped nul\0\""sv).takeString());
EXPECT_FALSE(Lexer("\"unescaped U+19\x19\""sv).takeString());
EXPECT_FALSE(Lexer("\"unescaped U+7f\x7f\""sv).takeString());
Expand Down
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