c++: nested lambda capturing a capture proxy, part 2 [PR94376]

  The r12-5403 fix apparently doesn't handle the case where the inner
lambda explicitly rather implicitly captures the capture proxy from
the outer lambda, and so we still reject the first example in the
testcase below.

The reason is that compared to an implicit capture, the effective
initializer for an explicit capture is wrapped in a location wrapper
(pointing to the source location of the explicit capture), and this
wrapper foils the is_capture_proxy check.  The simplest fix appears to
be to strip location wrappers accordingly.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?

	PR c++/94376

gcc/cp/ChangeLog:

	* lambda.c (lambda_capture_field_type): Strip location wrappers
	before checking for a capture proxy.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/lambda/lambda-nested9a.C: New test.
---
 gcc/cp/lambda.c                               |  1 +
 .../g++.dg/cpp0x/lambda/lambda-nested9a.C     | 42 +++++++++++++++++++
 2 files changed, 43 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C
  

On 12/15/21 15:36, Patrick Palka wrote:
> The r12-5403 fix apparently doesn't handle the case where the inner
> lambda explicitly rather implicitly captures the capture proxy from
> the outer lambda, and so we still reject the first example in the
> testcase below.
> 
> The reason is that compared to an implicit capture, the effective
> initializer for an explicit capture is wrapped in a location wrapper
> (pointing to the source location of the explicit capture), and this
> wrapper foils the is_capture_proxy check.  The simplest fix appears to
> be to strip location wrappers accordingly.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?
> 
> 	PR c++/94376
> 
> gcc/cp/ChangeLog:
> 
> 	* lambda.c (lambda_capture_field_type): Strip location wrappers
> 	before checking for a capture proxy.

I think either is_capture_proxy should strip location wrappers or 
gcc_checking_assert that it doesn't see one.

> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/lambda/lambda-nested9a.C: New test.
> ---
>   gcc/cp/lambda.c                               |  1 +
>   .../g++.dg/cpp0x/lambda/lambda-nested9a.C     | 42 +++++++++++++++++++
>   2 files changed, 43 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C
> 
> diff --git a/gcc/cp/lambda.c b/gcc/cp/lambda.c
> index c39a2bca416..7f2f927bda2 100644
> --- a/gcc/cp/lambda.c
> +++ b/gcc/cp/lambda.c
> @@ -221,6 +221,7 @@ lambda_capture_field_type (tree expr, bool explicit_init_p,
>       }
>     else
>       {
> +      STRIP_ANY_LOCATION_WRAPPER (expr);
>         if (!by_reference_p && is_capture_proxy (expr))
>   	{
>   	  /* When capturing by-value another capture proxy from an enclosing
> diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C
> new file mode 100644
> index 00000000000..d62f8f0c952
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C
> @@ -0,0 +1,42 @@
> +// PR c++/94376
> +// Like lambda-nested9.C but using explicit captures in the inner lambda.
> +// { dg-do compile { target c++11 } }
> +
> +int main() {
> +  // We used to incorrectly reject the first two cases.
> +  int i = 0;
> +  [=] () {
> +    [i] () mutable {
> +      ++i;
> +    };
> +  };
> +
> +#if __cpp_init_captures
> +  [j=0] () {
> +    [j] () mutable {
> +      ++j;
> +    };
> +  };
> +#endif
> +
> +  [=] () {
> +    [&i] () mutable {
> +      ++i; // { dg-error "read-only" }
> +    };
> +  };
> +
> +  const int j = 0;
> +  [=] () {
> +    [j] () mutable {
> +      ++j; // { dg-error "read-only" }
> +    };
> +  };
> +
> +#if __cpp_init_captures
> +  [j=0] () {
> +    [&j] () mutable {
> +      ++j; // { dg-error "read-only" "" { target c++14 } }
> +    };
> +  };
> +#endif
> +}
  

On Wed, 15 Dec 2021, Jason Merrill wrote:

> On 12/15/21 15:36, Patrick Palka wrote:
> > The r12-5403 fix apparently doesn't handle the case where the inner
> > lambda explicitly rather implicitly captures the capture proxy from
> > the outer lambda, and so we still reject the first example in the
> > testcase below.
> > 
> > The reason is that compared to an implicit capture, the effective
> > initializer for an explicit capture is wrapped in a location wrapper
> > (pointing to the source location of the explicit capture), and this
> > wrapper foils the is_capture_proxy check.  The simplest fix appears to
> > be to strip location wrappers accordingly.
> > 
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> > trunk?
> > 
> > 	PR c++/94376
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	* lambda.c (lambda_capture_field_type): Strip location wrappers
> > 	before checking for a capture proxy.
> 
> I think either is_capture_proxy should strip location wrappers or
> gcc_checking_assert that it doesn't see one.

Good idea, here's v2 which adds an assert to is_capture_proxy.  Only one
other caller, mark_const_cap_r, had to be adjusted.

-- >8 --

The r12-5403 fix apparently doesn't handle the case where the inner
lambda explicitly rather implicitly captures the capture proxy from
the outer lambda, which causes us to reject the first example in the
testcase below.

This is because compared to an implicit capture, the effective initializer
for an explicit capture is wrapped in a location wrapper (pointing to the
capture list), and this wrapper foils the is_capture_proxy check added in
r12-5403.

The simplest fix appears to be to strip location wrappers accordingly
before checking is_capture_proxy.  To help prevent against other
occurrences of this kind of bug, this patch also makes is_capture_proxy
assert it doesn't see a location wrapper.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?

	PR c++/94376

gcc/cp/ChangeLog:

	* lambda.c (lambda_capture_field_type): Strip location wrappers
	before checking for a capture proxy.
	(is_capture_proxy): Assert that we don't see a location wrapper.
	(mark_const_cap_r): Don't call is_constant_capture_proxy on a
	location wrapper.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/lambda/lambda-nested9a.C: New test.
---
 gcc/cp/lambda.c                               |  7 ++++
 .../g++.dg/cpp0x/lambda/lambda-nested9a.C     | 42 +++++++++++++++++++
 2 files changed, 49 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C

diff --git a/gcc/cp/lambda.c b/gcc/cp/lambda.c
index c39a2bca416..d14e12c48f0 100644
--- a/gcc/cp/lambda.c
+++ b/gcc/cp/lambda.c
@@ -221,6 +221,7 @@ lambda_capture_field_type (tree expr, bool explicit_init_p,
     }
   else
     {
+      STRIP_ANY_LOCATION_WRAPPER (expr);
       if (!by_reference_p && is_capture_proxy (expr))
 	{
 	  /* When capturing by-value another capture proxy from an enclosing
@@ -246,6 +247,10 @@ lambda_capture_field_type (tree expr, bool explicit_init_p,
 bool
 is_capture_proxy (tree decl)
 {
+  /* Location wrappers should be stripped or otherwise handled by the
+     caller before using this predicate.  */
+  gcc_checking_assert (!location_wrapper_p (decl));
+
   return (VAR_P (decl)
 	  && DECL_HAS_VALUE_EXPR_P (decl)
 	  && !DECL_ANON_UNION_VAR_P (decl)
@@ -1496,6 +1501,8 @@ mark_const_cap_r (tree *t, int *walk_subtrees, void *data)
 	  *walk_subtrees = 0;
 	}
     }
+  else if (location_wrapper_p (*t))
+    /* is_capture_proxy dislikes location wrappers.  */;
   else if (is_constant_capture_proxy (*t))
     var = DECL_CAPTURED_VARIABLE (*t);
 
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C
new file mode 100644
index 00000000000..d62f8f0c952
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C
@@ -0,0 +1,42 @@
+// PR c++/94376
+// Like lambda-nested9.C but using explicit captures in the inner lambda.
+// { dg-do compile { target c++11 } }
+
+int main() {
+  // We used to incorrectly reject the first two cases.
+  int i = 0;
+  [=] () {
+    [i] () mutable {
+      ++i;
+    };
+  };
+
+#if __cpp_init_captures
+  [j=0] () {
+    [j] () mutable {
+      ++j;
+    };
+  };
+#endif
+
+  [=] () {
+    [&i] () mutable {
+      ++i; // { dg-error "read-only" }
+    };
+  };
+
+  const int j = 0;
+  [=] () {
+    [j] () mutable {
+      ++j; // { dg-error "read-only" }
+    };
+  };
+
+#if __cpp_init_captures
+  [j=0] () {
+    [&j] () mutable {
+      ++j; // { dg-error "read-only" "" { target c++14 } }
+    };
+  };
+#endif
+}
  

On 12/16/21 11:28, Patrick Palka wrote:
> On Wed, 15 Dec 2021, Jason Merrill wrote:
> 
>> On 12/15/21 15:36, Patrick Palka wrote:
>>> The r12-5403 fix apparently doesn't handle the case where the inner
>>> lambda explicitly rather implicitly captures the capture proxy from
>>> the outer lambda, and so we still reject the first example in the
>>> testcase below.
>>>
>>> The reason is that compared to an implicit capture, the effective
>>> initializer for an explicit capture is wrapped in a location wrapper
>>> (pointing to the source location of the explicit capture), and this
>>> wrapper foils the is_capture_proxy check.  The simplest fix appears to
>>> be to strip location wrappers accordingly.
>>>
>>> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
>>> trunk?
>>>
>>> 	PR c++/94376
>>>
>>> gcc/cp/ChangeLog:
>>>
>>> 	* lambda.c (lambda_capture_field_type): Strip location wrappers
>>> 	before checking for a capture proxy.
>>
>> I think either is_capture_proxy should strip location wrappers or
>> gcc_checking_assert that it doesn't see one.
> 
> Good idea, here's v2 which adds an assert to is_capture_proxy.  Only one
> other caller, mark_const_cap_r, had to be adjusted.

OK.

> -- >8 --
> 
> The r12-5403 fix apparently doesn't handle the case where the inner
> lambda explicitly rather implicitly captures the capture proxy from
> the outer lambda, which causes us to reject the first example in the
> testcase below.
> 
> This is because compared to an implicit capture, the effective initializer
> for an explicit capture is wrapped in a location wrapper (pointing to the
> capture list), and this wrapper foils the is_capture_proxy check added in
> r12-5403.
> 
> The simplest fix appears to be to strip location wrappers accordingly
> before checking is_capture_proxy.  To help prevent against other
> occurrences of this kind of bug, this patch also makes is_capture_proxy
> assert it doesn't see a location wrapper.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?
> 
> 	PR c++/94376
> 
> gcc/cp/ChangeLog:
> 
> 	* lambda.c (lambda_capture_field_type): Strip location wrappers
> 	before checking for a capture proxy.
> 	(is_capture_proxy): Assert that we don't see a location wrapper.
> 	(mark_const_cap_r): Don't call is_constant_capture_proxy on a
> 	location wrapper.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/lambda/lambda-nested9a.C: New test.
> ---
>   gcc/cp/lambda.c                               |  7 ++++
>   .../g++.dg/cpp0x/lambda/lambda-nested9a.C     | 42 +++++++++++++++++++
>   2 files changed, 49 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C
> 
> diff --git a/gcc/cp/lambda.c b/gcc/cp/lambda.c
> index c39a2bca416..d14e12c48f0 100644
> --- a/gcc/cp/lambda.c
> +++ b/gcc/cp/lambda.c
> @@ -221,6 +221,7 @@ lambda_capture_field_type (tree expr, bool explicit_init_p,
>       }
>     else
>       {
> +      STRIP_ANY_LOCATION_WRAPPER (expr);
>         if (!by_reference_p && is_capture_proxy (expr))
>   	{
>   	  /* When capturing by-value another capture proxy from an enclosing
> @@ -246,6 +247,10 @@ lambda_capture_field_type (tree expr, bool explicit_init_p,
>   bool
>   is_capture_proxy (tree decl)
>   {
> +  /* Location wrappers should be stripped or otherwise handled by the
> +     caller before using this predicate.  */
> +  gcc_checking_assert (!location_wrapper_p (decl));
> +
>     return (VAR_P (decl)
>   	  && DECL_HAS_VALUE_EXPR_P (decl)
>   	  && !DECL_ANON_UNION_VAR_P (decl)
> @@ -1496,6 +1501,8 @@ mark_const_cap_r (tree *t, int *walk_subtrees, void *data)
>   	  *walk_subtrees = 0;
>   	}
>       }
> +  else if (location_wrapper_p (*t))
> +    /* is_capture_proxy dislikes location wrappers.  */;
>     else if (is_constant_capture_proxy (*t))
>       var = DECL_CAPTURED_VARIABLE (*t);
>   
> diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C
> new file mode 100644
> index 00000000000..d62f8f0c952
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nested9a.C
> @@ -0,0 +1,42 @@
> +// PR c++/94376
> +// Like lambda-nested9.C but using explicit captures in the inner lambda.
> +// { dg-do compile { target c++11 } }
> +
> +int main() {
> +  // We used to incorrectly reject the first two cases.
> +  int i = 0;
> +  [=] () {
> +    [i] () mutable {
> +      ++i;
> +    };
> +  };
> +
> +#if __cpp_init_captures
> +  [j=0] () {
> +    [j] () mutable {
> +      ++j;
> +    };
> +  };
> +#endif
> +
> +  [=] () {
> +    [&i] () mutable {
> +      ++i; // { dg-error "read-only" }
> +    };
> +  };
> +
> +  const int j = 0;
> +  [=] () {
> +    [j] () mutable {
> +      ++j; // { dg-error "read-only" }
> +    };
> +  };
> +
> +#if __cpp_init_captures
> +  [j=0] () {
> +    [&j] () mutable {
> +      ++j; // { dg-error "read-only" "" { target c++14 } }
> +    };
> +  };
> +#endif
> +}