Better diagnostics for iterators missing ++, !=, and * in range-based for loops.

[panzer]

Summary

This patch adds an additional note when ++begin, !=begin, *__begin, or the loop variable declaration is invalid, stating the high-level source of the error (e.g. "cannot use type T as an iterator; no operator ++ is defined"). Ideally, this would be the error message rather than a note, but this should be suffcient to clarify the existing errors.

[rsmith]

include/clang/Basic/DiagnosticSemaKinds.td

1427–1429

Perhaps this would be clearer if presented as a context-style note:

in implicit call to 'operator!=' for iterator of type %0

That'd also remove the issue that 'no viable operator' isn't necessarily the problem (it could be an ambiguous operator, or an inaccessible destructor, etc).

test/CXX/stmt.stmt/stmt.iter/stmt.ranged/p1.cpp

51

This note should presumably either say

loop variable 'a' has type 'char *'

or

loop variable 'a' is initialized by a value of type 'int'

Also, in these cases, it's not clear to me that this note is adding much value (since the primary diagnostic already mentions both relevant types). Are there other cases where the value is higher?

[panzer]

Changed wording according to rsmith's suggestions.

[panzer]

Changed the notes as per rsmith's suggestions.

include/clang/Basic/DiagnosticSemaKinds.td

1427–1429

Done. I feel it would be better still as the primary error message, if that becomes possible.

test/CXX/stmt.stmt/stmt.iter/stmt.ranged/p1.cpp

51

I wasn't sure about this note either, and I can't remember the case where it seemed necessary.

[dblaikie]

Looks like this was committed in r163350

include/clang/Basic/DiagnosticSemaKinds.td

 def err_for_range_dereference : Error<
   "invalid range expression of type %0; did you mean to dereference it "
   "with '*'?">;
+def note_for_range_invalid_iterator : Note <
+  "in implicit call to 'operator%select{!=|*|++}0' for iterator of type %1">;
 def note_for_range_begin_end : Note<
   "selected '%select{begin|end}0' %select{function|template }1%2 with iterator type %3">;
 

lib/Sema/SemaStmt.cpp

     NotEqExpr = ActOnBooleanCondition(S, ColonLoc, NotEqExpr.get());
     NotEqExpr = ActOnFinishFullExpr(NotEqExpr.get());
     if (NotEqExpr.isInvalid()) {
+      Diag(RangeLoc, diag::note_for_range_invalid_iterator)
+        << RangeLoc << 0 << BeginRangeRef.get()->getType();
       NoteForRangeBeginEndFunction(*this, BeginExpr.get(), BEF_begin);
       if (!Context.hasSameType(BeginType, EndType))
         NoteForRangeBeginEndFunction(*this, EndExpr.get(), BEF_end);    IncrExpr = ActOnUnaryOp(S, ColonLoc, tok::plusplus, BeginRef.get());

     IncrExpr = ActOnFinishFullExpr(IncrExpr.get());
     if (IncrExpr.isInvalid()) {
       Diag(RangeLoc, diag::note_for_range_invalid_iterator)
+        << RangeLoc << 2 << BeginRangeRef.get()->getType() ;
+      NoteForRangeBeginEndFunction(*this, BeginExpr.get(), BEF_begin);
       return StmtError();
     }
     ExprResult DerefExpr = ActOnUnaryOp(S, ColonLoc, tok::star, BeginRef.get());

     if (DerefExpr.isInvalid()) {
       Diag(RangeLoc, diag::note_for_range_invalid_iterator)
         << RangeLoc << 1 << BeginRangeRef.get()->getType();
+      NoteForRangeBeginEndFunction(*this, BeginExpr.get(), BEF_begin);
+      return StmtError();
     }
 
 

test/CXX/stmt.stmt/stmt.iter/stmt.ranged/p1.cpp

   };
   for (auto u : NoBegin()) { // expected-error {{range type 'NoBegin' has 'end' member but no 'begin' member}}
   }
-  for (auto u : NoEnd()) { // expected-error {{range type 'NoEnd' has 'begin' member but no 'end' member}}
+  for (auto u : NoEnd()) { // expected-error {{range type 'NoEnd' has 'begin' member but no 'end' member}} 
   }
 
   struct NoIncr {
     void *begin(); // expected-note {{selected 'begin' function with iterator type 'void *'}}
     void *end();
   };
-  for (auto u : NoIncr()) { // expected-error {{arithmetic on a pointer to void}}
+  for (auto u : NoIncr()) { // expected-error {{arithmetic on a pointer to void}}\
+    expected-note {{in implicit call to 'operator++' for iterator of type 'NoIncr'}}
   }
 
   struct NoNotEq {    NoNotEq end();

     void operator++();
   };
   for (auto u : NoNotEq()) { // expected-error {{invalid operands to binary expression}}\
-
+    expected-note {{in implicit call to 'operator!=' for iterator of type 'NoNotEq'}}
+  }
+
+  struct NoDeref {
+    NoDeref begin(); // expected-note {{selected 'begin' function}}
+    NoDeref end();
+    void operator++();
+    bool operator!=(NoDeref &);
+  };
+
+  for (auto u : NoDeref()) { // expected-error {{indirection requires pointer operand}} \
+    expected-note {{in implicit call to 'operator*' for iterator of type 'NoDeref'}}
+  }
 
   struct NoCopy {