[cfe-commits] PATCH #1 for "[sema++] clang should give a fixit for */& mismatch"

[Douglas Gregor]

On Jul 18, 2011, at 3:12 PM, Anna Zaks wrote:

> Attached is the updated patch. It includes the code review comments + sorting of the diagnostics based on the fixit info.
> 
> (No test for objective C since it will not result in the error, but a warning coming from a different location in the code. I'll add these fix to more errors/warnings later on.)
> 
> Thanks to everyone for the suggestions!
> Anna.
> <PR5941_2.diff>

This looks great! Only two minor comments, then please go ahead and commit.

Index: include/clang/Sema/Overload.h
===================================================================
--- include/clang/Sema/Overload.h	(revision 135431)
+++ include/clang/Sema/Overload.h	(working copy)
@@ -528,6 +528,12 @@
     ovl_fail_final_conversion_not_exact
   };
 
+  enum OverloadFixItKind {
+    ovl_fixit_undefined = 0,
+    ovl_fixit_dereference,
+    ovl_fixit_take_address
+  };
+

These should be named according to LLVM conventions (http://llvm.org/docs/CodingStandards.html#ll_naming), e.g., OFIK_Undefined, OFIK_Dereference, OFIK_TakeAddress.

+  // Check if the pointer to the argument needs to be passed
+  // (type -> type *) or (type & -> type *).
+  if (const PointerType *ToPtrTy = dyn_cast<PointerType>(ToQTy)) {
+    // Only suggest taking address of L-values.
+    if (!Arg->isLValue())
+      return false;
+
+    OpaqueValueExpr TmpExpr(Arg->getExprLoc(), FromQTy, VK_LValue);

This expression should be an rvalue, since &foo is an rvalue.

	- Doug


> On Jul 15, 2011, at 12:00 PM, Douglas Gregor wrote:
> 
>> 
>> On Jul 14, 2011, at 7:26 PM, Anna Zaks wrote:
>> 
>>> This patch is a first step towards providing FixItHints in case a function call is missing one/several * or & operators (See http://llvm.org/PR5941).
>>> 
>>> With this fix, the error message will display the function call. It will be followed by the list of notes - one for each possible candidate function declaration. If a function call can be fixed to match the particular declaration, a FixItHint will be provided along with the note. 
>> 
>> Very cool. Comments below.
>> 
>>> I also bumped up the number of MaxFixItHints to 6 (we need 2 FixIts per incorrect argument).
>>> 
>>> The remaining steps are:
>>> 1) Use FixIts when determining the order in which the notes should be displayed.
>>> 2) Find out if the same FixIts can be used with errors other then "error: no matching function for call to foo".
>> 
>> 
>> +def note_ovl_candidate_bad_conv_fixit : Note<"candidate "
>> +    "%select{function|function|constructor|"
>> +    "function |function |constructor |"
>> +    "constructor (the implicit default constructor)|"
>> +    "constructor (the implicit copy constructor)|"
>> +    "constructor (the implicit move constructor)|"
>> +    "function (the implicit copy assignment operator)|"
>> +    "function (the implicit move assignment operator)|"
>> +    "constructor (inherited)}0%1"
>> +    " not viable: no known conversion from %2 to %3 for "
>> +    "%select{%ordinal5 argument|object argument}4; "
>> +    "did you miss * or & operator%s6?">;
>> 
>> The diagnostic should suggest either * or &, depending on what would actually fix the code, rather than requiring the user to think about it further. This could be done with some kind of select, e.g.,
>> 
>> 	%select{|;dereference the argument with *|;take the address of the argument with &}7
>> 
>> which has the advantage of being extensible (e.g., in case we want to also suggest things like () to turn a function expression into a function call) and could even be tacked on to note_ovl_candidate_bad_conv rather than creating a new diagnostic.
>> 
>> Index: lib/Sema/SemaOverload.cpp
>> ===================================================================
>> --- lib/Sema/SemaOverload.cpp	(revision 135234)
>> +++ lib/Sema/SemaOverload.cpp	(working copy)
>> @@ -6730,6 +6730,54 @@
>> 
>> namespace {
>> 
>> +/// Update the Hints with FixIts to correct the given conversion. Return true
>> +/// on success.
>> +static bool TryToFixBadConversion(const Sema &S,
>> +                                  const ImplicitConversionSequence &Conv,
>> +                                  llvm::SmallVector<FixItHint, 4> &Hints) {
>> +  assert(Conv.isBad());
>> +  const Expr *Arg = Conv.Bad.FromExpr;
>> +  if (!Arg)
>> +    return false;
>> +
>> +  // The conversion is from argument type to parameter type.
>> +  const CanQualType FromQTy = S.Context.getCanonicalType(Conv.Bad
>> +                                                         .getFromType());
>> +  const CanQualType ToQTy = S.Context.getCanonicalType(Conv.Bad.getToType());
>> +
>> +  const SourceLocation Begin = Arg->getSourceRange().getBegin();
>> +  const SourceLocation End = S.PP.getLocForEndOfToken(Arg->getSourceRange()
>> +                                                      .getEnd());
>> +
>> +  // Check if the argument needs to be dereferenced
>> +  // (type * -> type) or (type * -> type &).
>> +  if (const CanQual<PointerType> FromPtrTy = FromQTy->getAs<PointerType>()) {
>> +    const CanQualType ToTy = ToQTy.getNonReferenceType();
>> +    const CanQualType FromTy = FromPtrTy->getPointeeType();
>> +    if (ToTy.getUnqualifiedType() == FromTy.getUnqualifiedType() &&
>> +        ToTy.isAtLeastAsQualifiedAs(FromTy)) {
>> 
>> It's probably worth loosening the type checking here slightly, to support (for example) derived-to-base conversions and Objective-C object pointer conversions. I suspect you'll want to factor that check out into a separate routine, since a similar check is needed for &.
>> 
>> +      Hints.push_back(FixItHint::CreateInsertion(Begin, "*("));
>> +      Hints.push_back(FixItHint::CreateInsertion(End, ")"));
>> +      return true;
>> +    }
>> +  }
>> 
>> The parentheses are necessary only in a few cases… can we perhaps whitelist common kinds of expressions (DeclRefExprs, ParenExprs, etc.) where the parentheses aren't needed, and then just emit the simple "*" in those cases? We want to try fairly hard to introduce the simplest, correct Fix-It we can.
>> 
>> +
>> +  // Check if the pointer to the argument needs to be passed
>> +  // (type -> type *) or (type & -> type *).
>> +  if (const CanQual<PointerType> ToPtrTy = ToQTy->getAs<PointerType>()) {
>> +    const CanQualType FromTy = FromQTy.getNonReferenceType();
>> +    const CanQualType ToTy = ToPtrTy->getPointeeType();
>> +    if (FromTy.getUnqualifiedType() == ToTy.getUnqualifiedType() &&
>> +        ToTy.isAtLeastAsQualifiedAs(FromTy)) {
>> +      Hints.push_back(FixItHint::CreateInsertion(Begin, "&("));
>> +      Hints.push_back(FixItHint::CreateInsertion(End, ")"));
>> +      return true;
>> +    }
>> +  }
>> +
>> 
>> For this case, we'll also need to check whether the expression is an lvalue (Expr::isLValue()), so that we don't produce a bogus fix-it for something like:
>> 
>> 	void f(int*);
>> 	void g() { f(17); } // can't apply the & operator here
>> 
>> Your patch is looking quite good; thanks for working on this!
>> 
>> 	- Doug
>