[Sema] Reword -Wrange-loop-analysis warning messages
Summary:
The messages for two of the warnings are misleading:
* warn_for_range_const_reference_copy suggests that the initialization
of the loop variable results in a copy. But that's not always true,
we just know that some conversion happens, potentially invoking a
constructor or conversion operator. The constructor might copy, as in
the example that lead to this message [1], but it might also not.
However, the constructed object is bound to a reference, which is
potentially misleading, so we rewrite the message to emphasize that.
We also make sure that we print the reference type into the warning
message to clarify that this warning only appears when operator*
returns a reference.
* warn_for_range_variable_always_copy suggests that a reference type
loop variable initialized from a temporary "is always a copy". But
we don't know this, the range might just return temporary objects
which aren't copies of anything. (Assuming RVO a copy constructor
might never have been called.)
The message for warn_for_range_copy is a bit repetitive: the type of a
VarDecl and its initialization Expr are the same up to cv-qualifiers,
because Sema will insert implicit casts or constructor calls to make
them match.
[1] https://bugs.llvm.org/show_bug.cgi?id=32823
Reviewers: aaron.ballman, Mordante, rtrieu
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D75613
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index ff64810..2104add 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -2741,22 +2741,24 @@
E = E->IgnoreImpCasts();
}
- bool ReturnsReference = false;
+ QualType ReferenceReturnType;
if (isa<UnaryOperator>(E)) {
- ReturnsReference = true;
+ ReferenceReturnType = SemaRef.Context.getLValueReferenceType(E->getType());
} else {
const CXXOperatorCallExpr *Call = cast<CXXOperatorCallExpr>(E);
const FunctionDecl *FD = Call->getDirectCallee();
QualType ReturnType = FD->getReturnType();
- ReturnsReference = ReturnType->isReferenceType();
+ if (ReturnType->isReferenceType())
+ ReferenceReturnType = ReturnType;
}
- if (ReturnsReference) {
+ if (!ReferenceReturnType.isNull()) {
// Loop variable creates a temporary. Suggest either to go with
// non-reference loop variable to indicate a copy is made, or
- // the correct time to bind a const reference.
- SemaRef.Diag(VD->getLocation(), diag::warn_for_range_const_reference_copy)
- << VD << VariableType << E->getType();
+ // the correct type to bind a const reference.
+ SemaRef.Diag(VD->getLocation(),
+ diag::warn_for_range_const_ref_binds_temp_built_from_ref)
+ << VD << VariableType << ReferenceReturnType;
QualType NonReferenceType = VariableType.getNonReferenceType();
NonReferenceType.removeLocalConst();
QualType NewReferenceType =
@@ -2769,7 +2771,7 @@
// Suggest removing the reference from the loop variable.
// If the type is a rvalue reference do not warn since that changes the
// semantic of the code.
- SemaRef.Diag(VD->getLocation(), diag::warn_for_range_variable_always_copy)
+ SemaRef.Diag(VD->getLocation(), diag::warn_for_range_ref_binds_ret_temp)
<< VD << RangeInitType;
QualType NonReferenceType = VariableType.getNonReferenceType();
NonReferenceType.removeLocalConst();
@@ -2821,7 +2823,7 @@
// Suggest changing from a const variable to a const reference variable
// if doing so will prevent a copy.
SemaRef.Diag(VD->getLocation(), diag::warn_for_range_copy)
- << VD << VariableType << InitExpr->getType();
+ << VD << VariableType;
SemaRef.Diag(VD->getBeginLoc(), diag::note_use_reference_type)
<< SemaRef.Context.getLValueReferenceType(VariableType)
<< VD->getSourceRange()
@@ -2841,9 +2843,10 @@
if (SemaRef.inTemplateInstantiation())
return;
- if (SemaRef.Diags.isIgnored(diag::warn_for_range_const_reference_copy,
- ForStmt->getBeginLoc()) &&
- SemaRef.Diags.isIgnored(diag::warn_for_range_variable_always_copy,
+ if (SemaRef.Diags.isIgnored(
+ diag::warn_for_range_const_ref_binds_temp_built_from_ref,
+ ForStmt->getBeginLoc()) &&
+ SemaRef.Diags.isIgnored(diag::warn_for_range_ref_binds_ret_temp,
ForStmt->getBeginLoc()) &&
SemaRef.Diags.isIgnored(diag::warn_for_range_copy,
ForStmt->getBeginLoc())) {