Scanner: Generate error on inbalanced RLO/LRO/PDF override markers.

Author: christianparpart

Changelog.md

@@ -3,6 +3,8 @@
 Compiler Features:
  * SMTChecker: Support named arguments in function calls.
 
+Language Features:
+ * Scanner: Generates a parser error when comments do contain an unbalanced or underflowing set of unicode direction override markers (LRO, RLO, PDF)
 
 ### 0.7.5 (2020-11-18)
 

liblangutil/CharStream.h

@@ -85,6 +85,19 @@ class CharStream
 	/// @returns The character of the current location after update is returned.
 	char setPosition(size_t _location);
 
+	/// Tests whether or not given octet sequence is present at the current reading position.
+	/// @returns true if the sequence could be found, false otherwise.
+	bool prefixMatch(std::string_view _sequence) const
+	{
+		if (m_position + _sequence.size() >= m_source.size())
+			return false;
+
+		for (size_t i = 0; i < _sequence.size(); ++i)
+			if (_sequence[i] != get(i))
+				return false;
+		return true;
+	}
+
 	void reset() { m_position = 0; }
 
 	std::string const& source() const noexcept { return m_source; }

liblangutil/Scanner.cpp

@@ -79,6 +79,8 @@ string to_string(ScannerError _errorCode)
 		case ScannerError::IllegalExponent: return "Invalid exponent.";
 		case ScannerError::IllegalNumberEnd: return "Identifier-start is not allowed at end of a number.";
 		case ScannerError::OctalNotAllowed: return "Octal numbers not allowed.";
+		case ScannerError::DirectionalOverrideUnderflowInComment: return "Unicode direction override underflow in comment.";
+		case ScannerError::DirectionalOverrideMismatchInComment: return "Mismatching directional override markers in comment.";
 		default:
 			solAssert(false, "Unhandled case in to_string(ScannerError)");
 			return "";
@@ -271,12 +273,74 @@ bool Scanner::skipWhitespaceExceptUnicodeLinebreak()
 	return sourcePos() != startPosition;
 }
 
+// A little helper class for counting depth of RLO/LRO/PDF uses.
+struct Scanner::UnicodeDirectionOverrideProcessor
+{
+	Scanner& scanner;
+	int rtlOverrideDepth = 0;
+
+	/// Tries to scan for an RLO/LRO/PDF and keeps track of script writing direction override depth.
+	///
+	/// @returns a 2-tuple indicating whether or not successfully some script writing direction
+	///          override has been consumed from the input and an error code in case
+	///          the input's lexical parser state is invalid and this error should be reported
+	///          to the user.
+	pair<bool, ScannerError> operator()()
+	{
+		// U+202D (LRO - Left-to-Right Override)
+		// U+202E (RLO - Right-to-Left Override)
+		if (
+			scanner.tryScanByteSequence("\xE2\x80\xAD") ||
+			scanner.tryScanByteSequence("\xE2\x80\xAE")
+		)
+		{
+			rtlOverrideDepth++;
+			return pair{true, ScannerError::NoError};
+		}
+		else if (scanner.tryScanByteSequence("\xE2\x80\xAC")) // U+202C (PDF - Pop Directional Formatting)
+		{
+			rtlOverrideDepth--;
+			if (rtlOverrideDepth < 0)
+				return pair{true, ScannerError::DirectionalOverrideUnderflowInComment};
+			else
+				return pair{true, ScannerError::NoError};
+		}
+		else
+			return pair{false, ScannerError::NoError};
+	}
+
+	ScannerError error() const noexcept
+	{
+		if (rtlOverrideDepth < 0)
+			return ScannerError::DirectionalOverrideUnderflowInComment;
+		else if (rtlOverrideDepth > 0)
+			return ScannerError::DirectionalOverrideMismatchInComment;
+		else
+			return ScannerError::NoError;
+	}
+};
+
 Token Scanner::skipSingleLineComment()
 {
+	UnicodeDirectionOverrideProcessor unicodeDirectionalOverride{*this};
+
 	// Line terminator is not part of the comment. If it is a
 	// non-ascii line terminator, it will result in a parser error.
 	while (!isUnicodeLinebreak())
-		if (!advance()) break;
+	{
+		auto const [processed, errorCode] = unicodeDirectionalOverride();
+		if (processed && errorCode != ScannerError::NoError)
+			return setError(errorCode);
+		else if (!processed)
+		{
+			if (!advance())
+				break;
+		}
+	}
+
+	if (unicodeDirectionalOverride.error() != ScannerError::NoError)
+		// Unbalanced RLO/LRO/PDF codepoint sequences in comment.
+		return setError(unicodeDirectionalOverride.error());
 
 	return Token::Whitespace;
 }
@@ -349,18 +413,30 @@ size_t Scanner::scanSingleLineDocComment()
 
 Token Scanner::skipMultiLineComment()
 {
+	UnicodeDirectionOverrideProcessor unicodeDirectionalOverride{*this};
+
 	while (!isSourcePastEndOfInput())
 	{
-		char ch = m_char;
-		advance();
-
-		// If we have reached the end of the multi-line comment, we
-		// consume the '/' and insert a whitespace. This way all
-		// multi-line comments are treated as whitespace.
-		if (ch == '*' && m_char == '/')
+		auto const [processed, errorCode] = unicodeDirectionalOverride();
+		if (processed && errorCode != ScannerError::NoError)
+			return setError(errorCode);
+		else if (!processed)
 		{
-			m_char = ' ';
-			return Token::Whitespace;
+			char ch = m_char;
+			advance();
+
+			// If we have reached the end of the multi-line comment, we
+			// consume the '/' and insert a whitespace. This way all
+			// multi-line comments are treated as whitespace.
+			if (ch == '*' && m_char == '/')
+			{
+				if (unicodeDirectionalOverride.error() != ScannerError::NoError)
+					// Unbalanced RLO/LRO/PDF codepoint sequences in comment.
+					return setError(unicodeDirectionalOverride.error());
+
+				m_char = ' ';
+				return Token::Whitespace;
+			}
 		}
 	}
 	// Unterminated multi-line comment.

liblangutil/Scanner.h

@@ -89,6 +89,9 @@ enum class ScannerError
 	IllegalExponent,
 	IllegalNumberEnd,
 
+	DirectionalOverrideUnderflowInComment,
+	DirectionalOverrideMismatchInComment,
+
 	OctalNotAllowed,
 };
 
@@ -183,6 +186,8 @@ class Scanner
 	///@}
 
 private:
+	struct UnicodeDirectionOverrideProcessor;
+
 	inline Token setError(ScannerError _error) noexcept
 	{
 		m_tokens[NextNext].error = _error;
@@ -248,6 +253,19 @@ class Scanner
 	/// Scans a slash '/' and depending on the characters returns the appropriate token
 	Token scanSlash();
 
+	/// Tries scanning given octet sequence and advances reading position respectively iff found.
+	/// @returns true if it could be scanned, false otherwise.
+	bool tryScanByteSequence(std::string_view _sequence)
+	{
+		if (!m_source->prefixMatch(_sequence))
+			return false;
+
+		for (size_t i = 0; i < _sequence.size(); ++i)
+			advance();
+
+		return true;
+	}
+
 	/// Scans an escape-sequence which is part of a string and adds the
 	/// decoded character to the current literal. Returns true if a pattern
 	/// is scanned.

scripts/test_antlr_grammar.sh

@@ -116,7 +116,9 @@ done < <(
   grep -riL -E \
     "^\/\/ (Syntax|Type|Declaration)Error|^\/\/ ParserError (2837|3716|3997|5333|6275|6281|6933|7319)|^==== Source:" \
     "${ROOT_DIR}/test/libsolidity/syntaxTests" \
-    "${ROOT_DIR}/test/libsolidity/semanticTests" \
+    "${ROOT_DIR}/test/libsolidity/semanticTests" |
+  grep -v -E 'comments/.*_unicode.*.sol'
+  # Skipping the unicode tests as I couldn't adapt the lexical grammar to recursively counting RLO/LRO/PDF's.
 )
 
 YUL_FILES=()

test/libsolidity/syntaxTests/comments/multiline_unicode_direction_override_1.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract C {
+    function f() public pure
+    {
+        // pop 1
+        /*underflow ‬*/
+    }
+}
+// ----
+// ParserError 8936: (137-152): Unicode direction override underflow in comment.

test/libsolidity/syntaxTests/comments/multiline_unicode_direction_override_2.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract C {
+    function f() public pure
+    {
+        // pop 2
+        /*underflow ‬‬*/
+    }
+}
+// ----
+// ParserError 8936: (137-152): Unicode direction override underflow in comment.

test/libsolidity/syntaxTests/comments/multiline_unicode_direction_override_3.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract C {
+    function f() public pure
+    {
+        // push 1
+        /*overflow ‮*/
+    }
+}
+// ----
+// ParserError 8936: (138-153): Mismatching directional override markers in comment.

test/libsolidity/syntaxTests/comments/multiline_unicode_direction_override_4.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract C {
+    function f() public pure
+    {
+        // push 2
+        /*overflow ‮‮*/
+    }
+}
+// ----
+// ParserError 8936: (138-156): Mismatching directional override markers in comment.

test/libsolidity/syntaxTests/comments/multiline_unicode_direction_override_5.sol

@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract C {
+    function f() public pure
+    {
+        // first push 1, then pop 1
+        /*ok ‮‬*/
+
+        // first push 2, then pop 2
+        /*ok ‮‮‬‬*/
+
+        // first push 3, then pop 3
+        /*ok ‮‮‮‬‬‬*/
+    }
+}
+// ----

test/libsolidity/syntaxTests/comments/multiline_unicode_direction_override_6.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract C {
+    function f() public pure
+    {
+        // first pop, then push
+        /*overflow ‬‮*/
+    }
+}
+// ----
+// ParserError 8936: (152-166): Unicode direction override underflow in comment.

test/libsolidity/syntaxTests/comments/singleline_unicode_direction_override_1.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract C {
+    function f() public pure
+    {
+        // pop 1
+        // underflow ‬
+    }
+}
+// ----
+// ParserError 8936: (137-153): Unicode direction override underflow in comment.

test/libsolidity/syntaxTests/comments/singleline_unicode_direction_override_2.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract C {
+    function f() public pure
+    {
+        // pop 2
+        // underflow ‬‬
+    }
+}
+// ----
+// ParserError 8936: (137-153): Unicode direction override underflow in comment.

test/libsolidity/syntaxTests/comments/singleline_unicode_direction_override_3.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract C {
+    function f() public pure
+    {
+        // push 1
+        // overflow ‮
+    }
+}
+// ----
+// ParserError 8936: (138-153): Mismatching directional override markers in comment.

test/libsolidity/syntaxTests/comments/singleline_unicode_direction_override_4.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract C {
+    function f() public pure
+    {
+        // push 2
+        // overflow ‮‮
+    }
+}
+// ----
+// ParserError 8936: (138-156): Mismatching directional override markers in comment.

test/libsolidity/syntaxTests/comments/singleline_unicode_direction_override_5.sol

@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract C {
+    function f() public pure
+    {
+        // first push 1, then pop 1
+        // ok ‮‬
+
+        // first push 2, then pop 2
+        // ok ‮‮‬‬
+
+        // first push 3, then pop 3
+        // ok ‮‮‮‬‬‬
+    }
+}
+// ----

test/libsolidity/syntaxTests/comments/singleline_unicode_direction_override_6.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.7.0;
+
+contract C {
+    function f() public pure
+    {
+        // first pop, then push
+        // underflow ‬‮
+    }
+}
+// ----
+// ParserError 8936: (152-168): Unicode direction override underflow in comment.