[libsolidity] ASTUtils: Adds helper to quickly locate closest ASTNode match for a byte offset into a SourceUnit.

libsolidity/ast/ASTUtils.cpp

@@ -17,6 +17,7 @@
 // SPDX-License-Identifier: GPL-3.0
 
 #include <libsolidity/ast/AST.h>
+#include <libsolidity/ast/ASTVisitor.h>
 #include <libsolidity/ast/ASTUtils.h>
 
 #include <libsolutil/Algorithms.h>
@@ -24,6 +25,40 @@
 namespace solidity::frontend
 {
 
+namespace
+{
+
+class ASTNodeLocator: public ASTConstVisitor
+{
+public:
+	explicit ASTNodeLocator(int _pos): m_offsetInFile{_pos}, m_innermostMatch{nullptr} {}
+
+	bool visitNode(ASTNode const& _node) override
+	{
+		// In the AST parent location always covers the whole child location.
+		// The parent is visited first so to get the innermost node we simply
+		// take the last one that still contains the offset.
+
+		if (!_node.location().containsOffset(m_offsetInFile))
+			return false;
+
+		m_innermostMatch = &_node;
+		return true;
+	}
+
+	int const m_offsetInFile;
+	ASTNode const* m_innermostMatch;
+};
+
+}
+
+ASTNode const* locateInnermostASTNode(int _pos, SourceUnit const& _sourceUnit)
+{
+	ASTNodeLocator locator{_pos};
+	_sourceUnit.accept(locator);
+	return locator.m_innermostMatch;
+}
+
 bool isConstantVariableRecursive(VariableDeclaration const& _varDecl)
 {
 	solAssert(_varDecl.isConstant(), "Constant variable expected");

libsolidity/ast/ASTUtils.h

@@ -21,9 +21,11 @@
 namespace solidity::frontend
 {
 
-class VariableDeclaration;
+class ASTNode;
 class Declaration;
 class Expression;
+class SourceUnit;
+class VariableDeclaration;
 
 /// Find the topmost referenced constant variable declaration when the given variable
 /// declaration value is an identifier. Works only for constant variable declarations.
@@ -33,4 +35,7 @@ VariableDeclaration const* rootConstVariableDeclaration(VariableDeclaration cons
 /// Returns true if the constant variable declaration is recursive.
 bool isConstantVariableRecursive(VariableDeclaration const& _varDecl);
 
+/// Teturns the innermost AST node that covers the given location or nullptr if not found.
+ASTNode const* locateInnermostASTNode(int _pos, SourceUnit const& _sourceUnit);
+
 }