DoDoENT added inline comments.
================
Comment at: clang/include/clang/AST/PrettyPrinter.h:307
+ /// decltype(s) will be printed as "S<Point{1,2}>" if enabled and as
"S<{1,2}>" if disabled,
+ /// regardless if PrintCanonicalTypes is enabled.
+ unsigned AlwaysIncludeTypeForNonTypeTemplateArgument : 1;
----------------
dblaikie wrote:
> aaron.ballman wrote:
> > DoDoENT wrote:
> > > aaron.ballman wrote:
> > > > dblaikie wrote:
> > > > > DoDoENT wrote:
> > > > > > dblaikie wrote:
> > > > > > > What does `PrintCanonicalTypes` have to do with this? Does it
> > > > > > > overlap with this functionality in some way, but doesn't provide
> > > > > > > the functionality you want in particular?
> > > > > > Thank you for the question. If you set the `PrintCanonicalTypes` to
> > > > > > `false`, the `S<Point{1, 2}>` would be printed as `S<Point{1, 2}>`
> > > > > > even without this patch. However, if you set it to `true`, it will
> > > > > > be printed as `S<{1, 2}>`.
> > > > > >
> > > > > > I don't fully understand why it does that, but it's quite annoying.
> > > > > >
> > > > > > For a better example, please take a look at the
> > > > > > `TemplateIdWithComplexFullTypeNTTP` unit tests that I've added: if
> > > > > > `PrintCanonicalTypes` is set to `true`, the original print output
> > > > > > of type is `NDArray<float, {{{0}}}, {{{0}}}, {{{0}}}>`, and if set
> > > > > > to `false` (which is default), the output is `NDArray<float,
> > > > > > Height{{{0}}}, Width{{{0}}}, Channels{{{0}}}>` - so the NTTP type
> > > > > > is neither fully written nor fully omitted, which is weird.
> > > > > >
> > > > > > As I said, I don't really understand the idea behind
> > > > > > `PrintCanonicalTypes`, but when my new
> > > > > > `AlwaysIncludeTypeForNonTypeTemplateArgument` is enabled, you will
> > > > > > get the full type printed, regardless of value of
> > > > > > `PrintCanonicalTypes` setting.
> > > > > >
> > > > > Perhaps this might be more of a bug in PrintCanonicalTypes than
> > > > > something to add a separate flag for.
> > > > >
> > > > > @aaron.ballman D55552 for context here...
> > > > >
> > > > > Hmm, actually, just adding the top level `Height{{0}}, Width{{0}},
> > > > > Channels{{0}}` is sufficient to make this code compile (whereas with
> > > > > the `{{{0}}}` it doesn't form a valid identifier.
> > > > >
> > > > > So what's your use case for needing more explicitness than that top
> > > > > level?
> > > > > Perhaps this might be more of a bug in PrintCanonicalTypes than
> > > > > something to add a separate flag for.
> > > > >
> > > > > @aaron.ballman D55552 for context here...
> > > >
> > > > I looked over D55552 again and haven't spotted anything with it that
> > > > seems amiss; the change there is to grab the canonical type before
> > > > trying to print it which is all the more I'd expect
> > > > `PrintCanonicalTypes` to impact.
> > > >
> > > > This looks like the behavior you'd get when you desugar the type. Check
> > > > out the AST dump for `s`: https://godbolt.org/z/vxh5j6qWr
> > > > ```
> > > > `-VarDecl <line:3:1, col:20> col:20 s 'S<Point{1, 2}>':'S<{1, 2}>'
> > > > callinit
> > > > ```
> > > > We generate that type information at
> > > > https://github.com/llvm/llvm-project/blob/main/clang/lib/AST/TextNodeDumper.cpp#L663
> > > > for doing the AST dump, note how the second type printed is the
> > > > desugared type and that matches what we're seeing from the pretty
> > > > printer.
> > > > So what's your use case for needing more explicitness than that top
> > > > level?
> > >
> > > As I described in the [github
> > > issue](https://github.com/llvm/llvm-project/issues/57562), I'm trying to
> > > write a clang-based tool that will have different behavior if the printed
> > > `{{{0}}}` is actually `Width` than if its `Height` or anything else.
> > >
> > > You can see the the issue in the AST dump for `bla`:
> > > https://godbolt.org/z/fMr4f13o3
> > >
> > > The type is
> > > ```
> > > `-VarDecl <line:20:1, col:21> col:21 bla 'NDArray<float,
> > > W>':'NDArray<float, {{{0}}}>' callinit
> > > `-CXXConstructExpr <col:21> 'NDArray<float, W>':'NDArray<float,
> > > {{{0}}}>' 'void () noexcept'
> > > ```
> > >
> > > so it's unknown whether `{{{0}}}` represent the `Width` or `Height`. My
> > > patch makes it work exactly like GCC (see the comparison of error message
> > > between [clang 15 and GCC 12.1](https://godbolt.org/z/WenWe8caf).
> > >
> > > > Perhaps this might be more of a bug in PrintCanonicalTypes than
> > > > something to add a separate flag for.
> > >
> > > This was also my first thought and the first version of my patch (before
> > > even submitting it here) was to actually change the behavior of
> > > `PrintCanonicalTypes`. However, that change made some tests fail, as I
> > > described in the patch description:
> > >
> > > - CodeGenCXX/debug-info-template.cpp
> > > - SemaCXX/constexpr-printing.cpp
> > > - SemaCXX/cxx2a-nttp-printing.cpp
> > > - SemaTemplate/temp_arg_string_printing.cpp
> > >
> > > Of course, it's possible to simply update the tests, but I actually don't
> > > fully understand what is the goal of `PrintCanonicalTypes` and whether
> > > its current behavior is actually desired or not, so I played it safe and
> > > introduced a new policy that is disabled by default until I get more
> > > feedback from more experienced LLVM developers.
> > >
> > > The patch does solve my problem and since I'm building LLVM from source
> > > anyway, I can have it enabled in my fork.
> > >
> > > I just want to see if it would also be beneficial to be introduced into
> > > the upstream LLVM.
> > > Of course, it's possible to simply update the tests, but I actually don't
> > > fully understand what is the goal of PrintCanonicalTypes and whether its
> > > current behavior is actually desired or not, so I played it safe and
> > > introduced a new policy that is disabled by default until I get more
> > > feedback from more experienced LLVM developers.
> >
> > `PrintCanonicalTypes` is what controls output like whether we print a
> > typedef name (not the canonical type) or the final underlying type all
> > typedefs involved (the canonical type). It won't have an impact on things
> > like whether we print the name of a structure or not.
> >
> > After looking into this, I think we do want changes here. I'm not 100%
> > convinced we need a new policy member. I tried out printing the type names
> > unconditionally and the results were a bit of a mixed bag (some diagnostics
> > got more clear, other diagnostics didn't become more clear but also didn't
> > become more confusing):
> > ```
> > error: 'note' diagnostics expected but not seen:
> > File
> > F:\source\llvm-project\clang\test\SemaTemplate\temp_arg_nontype_cxx20.cpp
> > Line 189: in instantiation of template class 'Diags::X<{1, 2}>' requested
> > here
> > error: 'note' diagnostics seen but not expected:
> > File
> > F:\source\llvm-project\clang\test\SemaTemplate\temp_arg_nontype_cxx20.cpp
> > Line 189: in instantiation of template class 'Diags::X<Diags::A{1, 2}>'
> > requested here
> > ```
> > seems like a clarifying change, while:
> > ```
> > error: 'error' diagnostics expected but not seen:
> > File F:\source\llvm-project\clang\test\SemaCXX\cxx2a-nttp-printing.cpp
> > Line 19: no member named 'display' in 'ASCII<{"this nontype template
> > argument is [...]"}>'
> > File F:\source\llvm-project\clang\test\SemaCXX\cxx2a-nttp-printing.cpp
> > Line 25: no member named 'display' in 'ASCII<{{119, 97, 105, 116, 32, 97,
> > 32, 115, 27, 99, ...}}>'
> > File F:\source\llvm-project\clang\test\SemaCXX\cxx2a-nttp-printing.cpp
> > Line 33: no member named 'display' in 'ASCII<{"what??!"}>'
> > error: 'error' diagnostics seen but not expected:
> > File F:\source\llvm-project\clang\test\SemaCXX\cxx2a-nttp-printing.cpp
> > Line 19: no member named 'display' in 'ASCII<Str<43>{"this nontype template
> > argument is [...]"}>'
> > File F:\source\llvm-project\clang\test\SemaCXX\cxx2a-nttp-printing.cpp
> > Line 25: no member named 'display' in 'ASCII<Str<14>{{119, 97, 105, 116,
> > 32, 97, 32, 115, 27, 99, ...}}>'
> > File F:\source\llvm-project\clang\test\SemaCXX\cxx2a-nttp-printing.cpp
> > Line 33: no member named 'display' in 'ASCII<Str<8>{"what??!"}>'
> > ```
> > seems like it's neither here nor there.
> >
> > @dblaikie, do you have feelings on how to go with this?
> Yeah, I'm inclined to think that `Diags::X<{1, 2}>` is just too simplified -
> it's unambiguous if the parameter isn't `auto`, but isn't valid syntax (so
> the language still expects a type name there) & so maybe we should do the
> same in diagnostics?
>
> @aaron.ballman - though I'm still confused by the behavior-change when
> `PrintCanonicalTypes = false` that causes the top level names to be printed?
> Maybe that's just a weird case/red herring/bug in `PrintCanonicalTypes =
> true` that skips those top level names and we could print them
> unconditionally?
>
> @DoDoENT - I was/am curious if/why you need more explicitness than would be
> provided by `PrintCanonicalTypes = false` - if the output was `NDArray<float,
> Height{{{0}}}, Width{{{0}}}, Channels{{{0}}}>` would that be sufficient for
> your needs? (I think in that case the name would be valid to use in code,
> which I think is a reasonable basis to make the decision - but I'm not sure
> how to justify adding all the intermediate names too)
>
> `PrintCanonicalTypes` is what controls output like whether we print a typedef
> name (not the canonical type) or the final underlying type all typedefs
> involved (the canonical type). It won't have an impact on things like whether
> we print the name of a structure or not.
Thank you for the explanation.
> I was/am curious if/why you need more explicitness than would be provided by
> `PrintCanonicalTypes = false` - if the output was `NDArray<float,
> Height{{{0}}}, Width{{{0}}}, Channels{{{0}}}>` would that be sufficient for
> your needs?
It would for now (at least until I actually start needing to get the types of
inner braces), however, in a real-world scenario I actually get output
`NDArray<float, {{{0}}}, {{{0}}}, {{{0}}}>`, regardless of the value of
`PrintCanonicalTypes`. I've tried to create a minimum reproducer for that case,
but, unfortunately, all simple cases resolve to actually display the names
`Height`, `Width`, etc. The closes thing to the real-world scenario is the
diagnostic message shown [here](https://godbolt.org/z/WenWe8caf).
However, in my real code, where there are multiple levels of type deduction
happening, I always get the output without a type name, regardless of the value
of `PrintCanonicalTypes`. This is why I took some time to debug what is
actually happening within clang and created this patch which now works for me
in all cases.
================
Comment at: clang/include/clang/AST/PrettyPrinter.h:307
+ /// decltype(s) will be printed as "S<Point{1,2}>" if enabled and as
"S<{1,2}>" if disabled,
+ /// regardless if PrintCanonicalTypes is enabled.
+ unsigned AlwaysIncludeTypeForNonTypeTemplateArgument : 1;
----------------
DoDoENT wrote:
> dblaikie wrote:
> > aaron.ballman wrote:
> > > DoDoENT wrote:
> > > > aaron.ballman wrote:
> > > > > dblaikie wrote:
> > > > > > DoDoENT wrote:
> > > > > > > dblaikie wrote:
> > > > > > > > What does `PrintCanonicalTypes` have to do with this? Does it
> > > > > > > > overlap with this functionality in some way, but doesn't
> > > > > > > > provide the functionality you want in particular?
> > > > > > > Thank you for the question. If you set the `PrintCanonicalTypes`
> > > > > > > to `false`, the `S<Point{1, 2}>` would be printed as `S<Point{1,
> > > > > > > 2}>` even without this patch. However, if you set it to `true`,
> > > > > > > it will be printed as `S<{1, 2}>`.
> > > > > > >
> > > > > > > I don't fully understand why it does that, but it's quite
> > > > > > > annoying.
> > > > > > >
> > > > > > > For a better example, please take a look at the
> > > > > > > `TemplateIdWithComplexFullTypeNTTP` unit tests that I've added:
> > > > > > > if `PrintCanonicalTypes` is set to `true`, the original print
> > > > > > > output of type is `NDArray<float, {{{0}}}, {{{0}}}, {{{0}}}>`,
> > > > > > > and if set to `false` (which is default), the output is
> > > > > > > `NDArray<float, Height{{{0}}}, Width{{{0}}}, Channels{{{0}}}>` -
> > > > > > > so the NTTP type is neither fully written nor fully omitted,
> > > > > > > which is weird.
> > > > > > >
> > > > > > > As I said, I don't really understand the idea behind
> > > > > > > `PrintCanonicalTypes`, but when my new
> > > > > > > `AlwaysIncludeTypeForNonTypeTemplateArgument` is enabled, you
> > > > > > > will get the full type printed, regardless of value of
> > > > > > > `PrintCanonicalTypes` setting.
> > > > > > >
> > > > > > Perhaps this might be more of a bug in PrintCanonicalTypes than
> > > > > > something to add a separate flag for.
> > > > > >
> > > > > > @aaron.ballman D55552 for context here...
> > > > > >
> > > > > > Hmm, actually, just adding the top level `Height{{0}}, Width{{0}},
> > > > > > Channels{{0}}` is sufficient to make this code compile (whereas
> > > > > > with the `{{{0}}}` it doesn't form a valid identifier.
> > > > > >
> > > > > > So what's your use case for needing more explicitness than that top
> > > > > > level?
> > > > > > Perhaps this might be more of a bug in PrintCanonicalTypes than
> > > > > > something to add a separate flag for.
> > > > > >
> > > > > > @aaron.ballman D55552 for context here...
> > > > >
> > > > > I looked over D55552 again and haven't spotted anything with it that
> > > > > seems amiss; the change there is to grab the canonical type before
> > > > > trying to print it which is all the more I'd expect
> > > > > `PrintCanonicalTypes` to impact.
> > > > >
> > > > > This looks like the behavior you'd get when you desugar the type.
> > > > > Check out the AST dump for `s`: https://godbolt.org/z/vxh5j6qWr
> > > > > ```
> > > > > `-VarDecl <line:3:1, col:20> col:20 s 'S<Point{1, 2}>':'S<{1, 2}>'
> > > > > callinit
> > > > > ```
> > > > > We generate that type information at
> > > > > https://github.com/llvm/llvm-project/blob/main/clang/lib/AST/TextNodeDumper.cpp#L663
> > > > > for doing the AST dump, note how the second type printed is the
> > > > > desugared type and that matches what we're seeing from the pretty
> > > > > printer.
> > > > > So what's your use case for needing more explicitness than that top
> > > > > level?
> > > >
> > > > As I described in the [github
> > > > issue](https://github.com/llvm/llvm-project/issues/57562), I'm trying
> > > > to write a clang-based tool that will have different behavior if the
> > > > printed `{{{0}}}` is actually `Width` than if its `Height` or anything
> > > > else.
> > > >
> > > > You can see the the issue in the AST dump for `bla`:
> > > > https://godbolt.org/z/fMr4f13o3
> > > >
> > > > The type is
> > > > ```
> > > > `-VarDecl <line:20:1, col:21> col:21 bla 'NDArray<float,
> > > > W>':'NDArray<float, {{{0}}}>' callinit
> > > > `-CXXConstructExpr <col:21> 'NDArray<float, W>':'NDArray<float,
> > > > {{{0}}}>' 'void () noexcept'
> > > > ```
> > > >
> > > > so it's unknown whether `{{{0}}}` represent the `Width` or `Height`. My
> > > > patch makes it work exactly like GCC (see the comparison of error
> > > > message between [clang 15 and GCC
> > > > 12.1](https://godbolt.org/z/WenWe8caf).
> > > >
> > > > > Perhaps this might be more of a bug in PrintCanonicalTypes than
> > > > > something to add a separate flag for.
> > > >
> > > > This was also my first thought and the first version of my patch
> > > > (before even submitting it here) was to actually change the behavior of
> > > > `PrintCanonicalTypes`. However, that change made some tests fail, as I
> > > > described in the patch description:
> > > >
> > > > - CodeGenCXX/debug-info-template.cpp
> > > > - SemaCXX/constexpr-printing.cpp
> > > > - SemaCXX/cxx2a-nttp-printing.cpp
> > > > - SemaTemplate/temp_arg_string_printing.cpp
> > > >
> > > > Of course, it's possible to simply update the tests, but I actually
> > > > don't fully understand what is the goal of `PrintCanonicalTypes` and
> > > > whether its current behavior is actually desired or not, so I played it
> > > > safe and introduced a new policy that is disabled by default until I
> > > > get more feedback from more experienced LLVM developers.
> > > >
> > > > The patch does solve my problem and since I'm building LLVM from source
> > > > anyway, I can have it enabled in my fork.
> > > >
> > > > I just want to see if it would also be beneficial to be introduced into
> > > > the upstream LLVM.
> > > > Of course, it's possible to simply update the tests, but I actually
> > > > don't fully understand what is the goal of PrintCanonicalTypes and
> > > > whether its current behavior is actually desired or not, so I played it
> > > > safe and introduced a new policy that is disabled by default until I
> > > > get more feedback from more experienced LLVM developers.
> > >
> > > `PrintCanonicalTypes` is what controls output like whether we print a
> > > typedef name (not the canonical type) or the final underlying type all
> > > typedefs involved (the canonical type). It won't have an impact on things
> > > like whether we print the name of a structure or not.
> > >
> > > After looking into this, I think we do want changes here. I'm not 100%
> > > convinced we need a new policy member. I tried out printing the type
> > > names unconditionally and the results were a bit of a mixed bag (some
> > > diagnostics got more clear, other diagnostics didn't become more clear
> > > but also didn't become more confusing):
> > > ```
> > > error: 'note' diagnostics expected but not seen:
> > > File
> > > F:\source\llvm-project\clang\test\SemaTemplate\temp_arg_nontype_cxx20.cpp
> > > Line 189: in instantiation of template class 'Diags::X<{1, 2}>' requested
> > > here
> > > error: 'note' diagnostics seen but not expected:
> > > File
> > > F:\source\llvm-project\clang\test\SemaTemplate\temp_arg_nontype_cxx20.cpp
> > > Line 189: in instantiation of template class 'Diags::X<Diags::A{1, 2}>'
> > > requested here
> > > ```
> > > seems like a clarifying change, while:
> > > ```
> > > error: 'error' diagnostics expected but not seen:
> > > File F:\source\llvm-project\clang\test\SemaCXX\cxx2a-nttp-printing.cpp
> > > Line 19: no member named 'display' in 'ASCII<{"this nontype template
> > > argument is [...]"}>'
> > > File F:\source\llvm-project\clang\test\SemaCXX\cxx2a-nttp-printing.cpp
> > > Line 25: no member named 'display' in 'ASCII<{{119, 97, 105, 116, 32, 97,
> > > 32, 115, 27, 99, ...}}>'
> > > File F:\source\llvm-project\clang\test\SemaCXX\cxx2a-nttp-printing.cpp
> > > Line 33: no member named 'display' in 'ASCII<{"what??!"}>'
> > > error: 'error' diagnostics seen but not expected:
> > > File F:\source\llvm-project\clang\test\SemaCXX\cxx2a-nttp-printing.cpp
> > > Line 19: no member named 'display' in 'ASCII<Str<43>{"this nontype
> > > template argument is [...]"}>'
> > > File F:\source\llvm-project\clang\test\SemaCXX\cxx2a-nttp-printing.cpp
> > > Line 25: no member named 'display' in 'ASCII<Str<14>{{119, 97, 105, 116,
> > > 32, 97, 32, 115, 27, 99, ...}}>'
> > > File F:\source\llvm-project\clang\test\SemaCXX\cxx2a-nttp-printing.cpp
> > > Line 33: no member named 'display' in 'ASCII<Str<8>{"what??!"}>'
> > > ```
> > > seems like it's neither here nor there.
> > >
> > > @dblaikie, do you have feelings on how to go with this?
> > Yeah, I'm inclined to think that `Diags::X<{1, 2}>` is just too simplified
> > - it's unambiguous if the parameter isn't `auto`, but isn't valid syntax
> > (so the language still expects a type name there) & so maybe we should do
> > the same in diagnostics?
> >
> > @aaron.ballman - though I'm still confused by the behavior-change when
> > `PrintCanonicalTypes = false` that causes the top level names to be
> > printed? Maybe that's just a weird case/red herring/bug in
> > `PrintCanonicalTypes = true` that skips those top level names and we could
> > print them unconditionally?
> >
> > @DoDoENT - I was/am curious if/why you need more explicitness than would be
> > provided by `PrintCanonicalTypes = false` - if the output was
> > `NDArray<float, Height{{{0}}}, Width{{{0}}}, Channels{{{0}}}>` would that
> > be sufficient for your needs? (I think in that case the name would be valid
> > to use in code, which I think is a reasonable basis to make the decision -
> > but I'm not sure how to justify adding all the intermediate names too)
> >
> > `PrintCanonicalTypes` is what controls output like whether we print a
> > typedef name (not the canonical type) or the final underlying type all
> > typedefs involved (the canonical type). It won't have an impact on things
> > like whether we print the name of a structure or not.
>
> Thank you for the explanation.
>
> > I was/am curious if/why you need more explicitness than would be provided
> > by `PrintCanonicalTypes = false` - if the output was `NDArray<float,
> > Height{{{0}}}, Width{{{0}}}, Channels{{{0}}}>` would that be sufficient for
> > your needs?
>
> It would for now (at least until I actually start needing to get the types of
> inner braces), however, in a real-world scenario I actually get output
> `NDArray<float, {{{0}}}, {{{0}}}, {{{0}}}>`, regardless of the value of
> `PrintCanonicalTypes`. I've tried to create a minimum reproducer for that
> case, but, unfortunately, all simple cases resolve to actually display the
> names `Height`, `Width`, etc. The closes thing to the real-world scenario is
> the diagnostic message shown [here](https://godbolt.org/z/WenWe8caf).
>
> However, in my real code, where there are multiple levels of type deduction
> happening, I always get the output without a type name, regardless of the
> value of `PrintCanonicalTypes`. This is why I took some time to debug what is
> actually happening within clang and created this patch which now works for me
> in all cases.
> Maybe that's just a weird case/red herring/bug in `PrintCanonicalTypes =
> true` that skips those top level names and we could print them
> unconditionally?
From my debugging sessions, I saw that the difference happens during printing
whether the type in question is deduced type or known type. If it's a known
type, then in both cases the type gets printed (in a clang-based tool, not in
the diagnostic as shown on Godbolt). However, if it's a deduced type, then the
type gets or doesn't get printed depending on whether the canonical type is
requested. If canonical type is requested from a deduced type, in AST it's
actually represented as an "expression statement", not a "type", and then the
type printer tries to print it as an "expression statement". This then leads to
printing code in APValue and TemplateBase thinking that it's actually printing
a normal C++ expression (as in the case of a clang-tidy or similar refactor
tool), and not as a non-type template parameter, yielding printout with omitted
types, as that is generally expected when writing code.
However, if you are using the printer to get a full type name in a string for
different purposes, as I do, then you get incomplete information. So, there may
be cases when you actually need/want full-type info and cases when you don't
want it. Therefore, I think some new policy config should be in place to let
people choose the behavior.
Repository:
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