Change the behavior of implicit int diagnostics

C89 allowed a type specifier to be elided with the resulting type being
int, aka implicit int behavior. This feature was subsequently removed
in C99 without a deprecation period, so implementations continued to
support the feature. Now, as with implicit function declarations, is a
good time to reevaluate the need for this support.

This patch allows -Wimplicit-int to issue warnings in C89 mode (off by
default), defaults the warning to an error in C99 through C17, and
disables support for the feature entirely in C2x. It also removes a
warning about missing declaration specifiers that really was just an
implicit int warning in disguise and other minor related cleanups.

1 files changed, 2 insertions, 2 deletions

diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 2b386c8..3d18ffe 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -2637,8 +2637,8 @@ bool Parser::ParseImplicitInt(DeclSpec &DS, CXXScopeSpec *SS,
   // error, do lookahead to try to do better recovery. This never applies
   // within a type specifier. Outside of C++, we allow this even if the
   // language doesn't "officially" support implicit int -- we support
-  // implicit int as an extension in C99 and C11.
-  if (!isTypeSpecifier(DSC) && !getLangOpts().CPlusPlus &&
+  // implicit int as an extension in some language modes.
+  if (!isTypeSpecifier(DSC) && getLangOpts().isImplicitIntAllowed() &&
       isValidAfterIdentifierInDeclarator(NextToken())) {
     // If this token is valid for implicit int, e.g. "static x = 4", then
     // we just avoid eating the identifier, so it will be parsed as the