rsmith added a comment.
Please take a look at
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0588r1.html, which
respecifies the rules for lambda capture and its interaction with default
arguments, and has been voted into the C++ working paper as a defect report
resolution. The approach there is to use a purely syntactic, scope-based
mechanism to detect problems such as this. (In dependent contexts, we can track
on the `DeclRefExpr` whether the name is odr-usable, in case we can't tell
whether it's odr-used from the template definition alone.)
================
Comment at: include/clang/Sema/Sema.h:1062
+
+ const DeclContext *ParentOfDefaultArg = nullptr;
+
----------------
There are lots of cases where we switch context in the middle of handling an
expression, for instance to instantiate a template (or even *parse* a template
in MSVC-compatible delayed template parsing mode). It's not reasonable to add a
new form of state that all those places will need to save and restore
themselves.
Please consider whether this would make sense as a member of the
`ExpressionEvaluationContextRecord` or similar.
================
Comment at: lib/Sema/SemaExpr.cpp:4520-4541
+ // Add mappings for instantiated parameters appearing before Param. This
+ // is needed to instantiate default argument expressions referencing
+ // other parameters in unevaluated contexts.
+ if (FunctionDecl *Pattern = FD->getTemplateInstantiationPattern()) {
+ auto I = FD->param_begin();
+ for (const auto *PVD : Pattern->parameters()) {
+ if (*I == Param)
----------------
Use `addInstantiatedParametersToScope` for this.
This bugfix looks to be independent of the fix for lambdas; can you factor it
out into a separate patch?
https://reviews.llvm.org/D36915
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