[clang] [dataflow] Parse formulas from text (PR #66424)

[Gábor Horváth via cfe-commits]

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@@ -95,4 +98,94 @@ BoolValue &Arena::makeBoolValue(const Formula &F) {
   return *It->second;
 }
 
+namespace {
+const Formula *parse(Arena &A, llvm::StringRef &In) {
+  auto EatWhitespace = [&] { In = In.ltrim(' '); };
+  EatWhitespace();
+
+  if (In.consume_front("!")) {
+    if (auto *Arg = parse(A, In))
+      return &A.makeNot(*Arg);
+    return nullptr;
+  }
+
+  if (In.consume_front("(")) {
+    auto *Arg1 = parse(A, In);
+    if (!Arg1)
+      return nullptr;
+
+    EatWhitespace();
+    decltype(&Arena::makeOr) Op;
+    if (In.consume_front("|"))
+      Op = &Arena::makeOr;
+    else if (In.consume_front("&"))
+      Op = &Arena::makeAnd;
+    else if (In.consume_front("=>"))
+      Op = &Arena::makeImplies;
+    else if (In.consume_front("="))
+      Op = &Arena::makeEquals;
+    else
+      return nullptr;
+
+    auto *Arg2 = parse(A, In);
+    if (!Arg2)
+      return nullptr;
+
+    EatWhitespace();
+    if (!In.consume_front(")"))
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Xazax-hun wrote:

Not required for this PR, but it would be great if it could do basic diagnostics like `')' expected at post Y`. 

https://github.com/llvm/llvm-project/pull/66424