[P4Testgen] Move static helpers from TestgenTarget and ProgramInfo to common/lib/utils

[vlstill]

The utility function TestgenTarget::argumentsToTypeDeclarations can be also useful outside of the TestgenTarget. Similarly the three static functions in ProgramInfo: findProgramDecl (two overloads) and resolveProgramType. This PR makes them available in common/lib/utils.h.

Porting to changes

• TestgenTarget::argumentsToTypeDeclarations is replaced with freestanding argumentsToTypeDeclarations that returns the list of declarations instead of using output parameter
• ProgramInfo::findProgramDecl (two overloads) and ProgramInfo::resolveProgramType are now freestanding functions
• all of the functions are declared in backends/p4tools/common/lib/utils.h

[fruffy]

Could you move this to common/lib/util.h instead?

[vlstill]

I've tried that originally. However this depends on a static method from programInfo. Maybe that one could be extracted too, but otherwise this is testgen-specific.

[fruffy]

I've tried that originally. However this depends on a static method from programInfo. Maybe that one could be extracted too, but otherwise this is testgen-specific.

Hmm, ideally I would like to also add a general ProgramInfo in the common folder, since I have been using a form of it for three modules now. But for now we can just move these static helpers:

/// Looks up a declaration from a path. A BUG occurs if no declaration is found.
static const IR::IDeclaration *findProgramDecl(const IR::IGeneralNamespace *ns,
                                               const IR::Path *path);

/// Looks up a declaration from a path expression. A BUG occurs if no declaration is found.
static const IR::IDeclaration *findProgramDecl(const IR::IGeneralNamespace *ns,
                                               const IR::PathExpression *pathExpr);

/// Resolves a Type_Name in the current environment.
static const IR::Type_Declaration *resolveProgramType(const IR::IGeneralNamespace *ns,
                                                      const IR::Type_Name *type);

[vlstill]

yep. I think moving the helpers now makes sense