arphaman created this revision.
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This patch avoids the -Wshadow warning for variables which shadow variables
that aren't captured by lambdas with an explicit capture list. It provides an
additional note that points to location of the explicit capture.
I noticed that we have -Wshadow-all as well, but I wasn't sure how to preserve
the old behaviour for it (since I don't think I can check if a diagnostic group
is enabled), or if the old behaviour should be preserved at all. What do you
think?
This patch fixes PR 21426, but I think that this is a partial fix, since that
bug doesn't specify that the capture list should be explicit. I plan on working
on a similar patch for lambdas with a default capture specifier and implicit
variable captures, but I'm not sure it's 100% needed for them. Do you think
this kind of change would make sense for implicit captures as well?
Repository:
rL LLVM
https://reviews.llvm.org/D26278
Files:
include/clang/Basic/DiagnosticSemaKinds.td
lib/Sema/SemaDecl.cpp
test/SemaCXX/warn-shadow-in-lambdas.cpp
Index: test/SemaCXX/warn-shadow-in-lambdas.cpp
===================================================================
--- /dev/null
+++ test/SemaCXX/warn-shadow-in-lambdas.cpp
@@ -0,0 +1,62 @@
+// RUN: %clang_cc1 -std=c++14 -verify -fsyntax-only -Wshadow %s
+
+void foo(int param) { // expected-note 1+ {{previous declaration is here}}
+ int var = 0; // expected-note 1+ {{previous declaration is here}}
+
+ // Warn for lambdas with a default capture specifier.
+ {
+ auto f1 = [=] { int var = 1; }; // expected-warning {{declaration shadows a local variable}}
+ auto f2 = [&] { int var = 2; }; // expected-warning {{declaration shadows a local variable}}
+ auto f3 = [=] (int param) { ; }; // expected-warning {{declaration shadows a local variable}}
+ auto f4 = [&] (int param) { ; }; // expected-warning {{declaration shadows a local variable}}
+ }
+
+ // Warn normally inside of lambdas.
+ auto l1 = [] { // expected-note {{previous declaration is here}}
+ int x = 1; // expected-note {{previous declaration is here}}
+ { int x = 2; } // expected-warning {{declaration shadows a local variable}}
+ };
+ auto l2 = [] (int x) { // expected-note {{previous declaration is here}}
+ { int x = 1; } // expected-warning {{declaration shadows a local variable}}
+ };
+
+ // Avoid warnings for variables that aren't explicitly captured.
+ {
+ auto f1 = [] { int var = 1; }; // no warning
+ auto f2 = [] (int param) { ; }; // no warning
+ auto f3 = [param] () { int var = 1; }; // no warning
+ auto f4 = [var] (int param) { ; }; // no warning
+ };
+
+ // Warn for variables that are explicitly captured.
+ {
+ auto f1 = [var] () { // expected-note {{variable 'var' is explicitly captured here}}
+ int var = 1; // expected-warning {{declaration shadows a local variable}}
+ };
+ auto f2 = [param] // expected-note {{variable 'param' is explicitly captured here}}
+ (int param) { ; }; // expected-warning {{declaration shadows a local variable}}
+ }
+
+ // Warn for variables defined in the capture list.
+ auto l3 = [z = var] { // expected-note {{previous declaration is here}}
+ int var = 1; // no warning
+ { int z = 1; } // expected-warning {{declaration shadows a local variable}}
+ };
+ auto l4 = [var = param] (int param) { ; }; // no warning
+
+ // Make sure that inner lambdas work as well.
+ auto l5 = [var, l1] { // expected-note {{variable 'l1' is explicitly captured here}}
+ auto l1 = [] { // expected-warning {{declaration shadows a local variable}}
+ int var = 1; // no warning
+ };
+ auto f1 = [] { int var = 1; }; // no warning
+ auto f2 = [=] { int var = 1; }; // expected-warning {{declaration shadows a local variable}}
+ auto f3 = [var] // expected-note {{variable 'var' is explicitly captured here}}
+ { int var = 1; }; // expected-warning {{declaration shadows a local variable}}
+ };
+
+ // Generic lambda arguments should work.
+ auto g1 = [](auto param) { ; }; // no warning
+ auto g2 = [param] // expected-note {{variable 'param' is explicitly captured here}}
+ (auto param) { ; }; // expected-warning {{declaration shadows a local variable}}
+}
Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -6582,6 +6582,17 @@
return OldDC->isFileContext() ? SDK_Global : SDK_Local;
}
+/// Return the location of the capture if the given lambda captures the given
+/// variable \p VD, or an invalid source location otherwise.
+static SourceLocation getCaptureLocation(const LambdaScopeInfo *LSI,
+ const VarDecl *VD) {
+ for (const LambdaScopeInfo::Capture &Capture : LSI->Captures) {
+ if (Capture.isVariableCapture() && Capture.getVariable() == VD)
+ return Capture.getLocation();
+ }
+ return SourceLocation();
+}
+
/// \brief Diagnose variable or built-in function shadowing. Implements
/// -Wshadow.
///
@@ -6640,6 +6651,21 @@
DeclContext *OldDC = ShadowedDecl->getDeclContext();
+ SourceLocation CaptureLoc;
+ if (isa<VarDecl>(ShadowedDecl) && NewDC && isa<CXXMethodDecl>(NewDC)) {
+ if (const auto *RD = dyn_cast<CXXRecordDecl>(NewDC->getParent())) {
+ // Try to avoid warnings for lambdas with an explicit capture list.
+ if (RD->isLambda() && OldDC->Encloses(NewDC->getLexicalParent()) &&
+ RD->getLambdaCaptureDefault() == LCD_None) {
+ const auto *LSI = cast<LambdaScopeInfo>(getCurFunction());
+ // Warn only when the lambda captures the shadowed decl explicitly.
+ CaptureLoc = getCaptureLocation(LSI, cast<VarDecl>(ShadowedDecl));
+ if (CaptureLoc.isInvalid())
+ return;
+ }
+ }
+ }
+
// Only warn about certain kinds of shadowing for class members.
if (NewDC && NewDC->isRecord()) {
// In particular, don't warn about shadowing non-class members.
@@ -6662,6 +6688,8 @@
return;
ShadowedDeclKind Kind = computeShadowedDeclKind(ShadowedDecl, OldDC);
Diag(R.getNameLoc(), diag::warn_decl_shadow) << Name << Kind << OldDC;
+ if (!CaptureLoc.isInvalid())
+ Diag(CaptureLoc, diag::note_var_explicitly_captured_here) << Name;
Diag(ShadowedDecl->getLocation(), diag::note_previous_declaration);
}
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -6227,6 +6227,8 @@
def note_lambda_to_block_conv : Note<
"implicit capture of lambda object due to conversion to block pointer "
"here">;
+ def note_var_explicitly_captured_here : Note<"variable %0 is explicitly "
+ "captured here">;
// C++14 lambda init-captures.
def warn_cxx11_compat_init_capture : Warning<
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