vedgy added inline comments.
================
Comment at: clang/include/clang-c/Index.h:329
+ * CXIndexOptions Opts = { sizeof(CXIndexOptions),
+ * clang_getDefaultGlobalOptions() };
+ * \endcode
----------------
aaron.ballman wrote:
> vedgy wrote:
> > vedgy wrote:
> > > aaron.ballman wrote:
> > > > vedgy wrote:
> > > > > When I almost finished the requested changes, I remembered that the
> > > > > return value of `clang_getDefaultGlobalOptions()` depends on
> > > > > environment variables, and thus `0` is not necessarily the default.
> > > > > Adjusted the changes and updated this revision.
> > > > >
> > > > > Does the extra requirement to non-zero initialize this second member
> > > > > sway your opinion on the usefulness of the helper function `inline
> > > > > CXIndexOptions clang_getDefaultIndexOptions()`? Note that there may
> > > > > be same (environment) or other important reasons why future new
> > > > > options couldn't be zeroes by default.
> > > > Thinking out loud a bit... (potentially bad idea incoming)
> > > >
> > > > What if we dropped `clang_getDefaultGlobalOptions()` and instead made a
> > > > change to `CXGlobalOptFlags`:
> > > > ```
> > > > typedef enum {
> > > > /**
> > > > * Used to indicate that the default CXIndex options are used. By
> > > > default, no
> > > > * global options will be used. However, environment variables may
> > > > change which
> > > > * global options are in effect at runtime.
> > > > */
> > > > CXGlobalOpt_Default = 0x0,
> > > >
> > > > /**
> > > > * Used to indicate that threads that libclang creates for indexing
> > > > * purposes should use background priority.
> > > > *
> > > > * Affects #clang_indexSourceFile, #clang_indexTranslationUnit,
> > > > * #clang_parseTranslationUnit, #clang_saveTranslationUnit.
> > > > */
> > > > CXGlobalOpt_ThreadBackgroundPriorityForIndexing = 0x1,
> > > >
> > > > /**
> > > > * Used to indicate that threads that libclang creates for editing
> > > > * purposes should use background priority.
> > > > *
> > > > * Affects #clang_reparseTranslationUnit, #clang_codeCompleteAt,
> > > > * #clang_annotateTokens
> > > > */
> > > > CXGlobalOpt_ThreadBackgroundPriorityForEditing = 0x2,
> > > >
> > > > /**
> > > > * Used to indicate that all threads that libclang creates should use
> > > > * background priority.
> > > > */
> > > > CXGlobalOpt_ThreadBackgroundPriorityForAll =
> > > > CXGlobalOpt_ThreadBackgroundPriorityForIndexing |
> > > > CXGlobalOpt_ThreadBackgroundPriorityForEditing,
> > > >
> > > > /**
> > > > * Used to indicate that no global options should be used, even
> > > > * in the presence of environment variables.
> > > > */
> > > > CXGlobalOpt_None = 0xFFFFFFFF
> > > > } CXGlobalOptFlags;
> > > > ```
> > > > so that when the user passes `0` they get the previous behavior.
> > > >
> > > > `clang_CXIndex_setGlobalOptions()` would remain deprecated.
> > > > `clang_CXIndex_getGlobalOptions()` would be interesting though -- would
> > > > it return `CXGlobalOpt_None` or `CXGlobalOpt_Default` in the event the
> > > > index was created without any global options? Hmmm.
> > > >
> > > > Err, actually, I suppose this won't work too well because then code
> > > > silently changes behavior if it does
> > > > `clang_CXIndex_setGlobalOptions(CXGlobalOpt_None);` because that would
> > > > change from "do what the environment says" to "ignore the environment".
> > > > But I have to wonder whether anyone actually *does* that or not... my
> > > > intuition is that folks would not call
> > > > `clang_CXIndex_setGlobalOptions()` at all unless they were setting an
> > > > option to a non-none value. We could rename `CXGlobalOpt_None` to
> > > > `CXGlobalOpt_Nothing` (or something along those lines) to force a
> > > > compilation error, but that's a bit of a nuclear option for what's
> > > > supposed to be a stable API.
> > > >
> > > > So I'm on the fence, I guess. I'd still prefer for zero to give
> > > > sensible defaults and I don't think there's enough use of the global
> > > > options + environment variables to matter. But I also don't like
> > > > silently breaking code, so my idea above may be a nonstarter.
> > > >
> > > > I suppose another possible idea is: deprecate the notion of global
> > > > options enum and setter/getter entirely, add two new fields to
> > > > `CXIndexOptions`:
> > > > ```
> > > > typedef enum {
> > > > CXChoice_Default = 0,
> > > > CXChoice_Enabled = 1,
> > > > CXChoice_Disabled = 2
> > > > } CXChoice;
> > > >
> > > > ...
> > > > unsigned ThreadPriorityBackgroundForIndexing;
> > > > unsigned ThreadPriorityBackgroundForEditing;
> > > > ...
> > > > ```
> > > > so that `0` gives the correct default behavior based on environment
> > > > variable. There would be no global setter or getter for this
> > > > information (and we'd eventually remove
> > > > `clang_CXIndex_[gs]etGlobalOptions()`).
> > > > I suppose this won't work too well because then code silently changes
> > > > behavior if it does `clang_CXIndex_setGlobalOptions(CXGlobalOpt_None);`
> > > > because that would change from "do what the environment says" to
> > > > "ignore the environment".
> > > No, the current consequence of such a call already is to ignore the
> > > environment. What would change is the consequence of calling
> > > `clang_CXIndex_setGlobalOptions(0);` - from "ignore the environment" to
> > > "do what the environment says".
> > >
> > > > But I have to wonder whether anyone actually *does* that or not... my
> > > > intuition is that folks would not call
> > > > `clang_CXIndex_setGlobalOptions()` at all unless they were setting an
> > > > option to a non-none value.
> > > I agree. Possible unlikely reasons to call
> > > `clang_CXIndex_setGlobalOptions(0)` are:
> > > 1) in case the environment variables are set for some other program;
> > > 2) in case setting the environment variables had been useful in the past
> > > but not in the latest and greatest version of an IDE;
> > > 3) if background priority is never useful for an IDE.
> > >
> > > > I suppose another possible idea is: deprecate the notion of global
> > > > options enum and setter/getter entirely, add two new fields to
> > > > CXIndexOptions
> > > This appears to be a great idea to me. The notion of `CXGlobalOptFlags`
> > > somewhat conflicts with the new `CXIndexOptions` struct, in which two
> > > other boolean options are represented by bit-fields.
> > >
> > > I think we can forbid from the start calling
> > > `clang_CXIndex_[gs]etGlobalOptions()` if the index is created via the new
> > > function `clang_createIndexWithOptions`.
> > >
> > > If 3-state environment variables (unspecified/on/off) are introduced in
> > > the future, `CXChoice` could be extended with
> > > `CXChoice_FromEnvironmentOrEnabled = 3` to indicate that if the
> > > environment variable is present, its value should be respected, otherwise
> > > the thread priority should be enabled.
> > >
> > > `CXChoice` cannot possibly have many valid values. So how about:
> > > ```
> > > unsigned char ThreadPriorityBackgroundForIndexing;
> > > unsigned char ThreadPriorityBackgroundForEditing;
> > > ```
> > > Then `size_t Size` could become `unsigned Size` and all non-pointer
> > > options would fit into 8 bytes on x86_64.
> > >
> > > Did you reorder the words in the variable names intentionally?
> > > `CXGlobalOpt_ThreadBackgroundPriorityForIndexing` =>
> > > `ThreadPriorityBackgroundForIndexing`
> > Perhaps `clang_CXIndex_getGlobalOptions()` should not be deprecated. It
> > would allow the application to learn which priorities are actually used by
> > libclang.
> > I think we can forbid from the start calling
> > clang_CXIndex_[gs]etGlobalOptions() if the index is created via the new
> > function clang_createIndexWithOptions.
>
> I think that would be great, at least for the setter. As you mention, we
> might not want to deprecate the getter (so long as it reports accurate
> information to the caller) because that could be useful still. However, I was
> also thinking that same logic could apply (at least in theory) to other
> options in the structure and so we might want to deprecate it with a
> replacement that gets all of the options from the index at once. However,
> that felt like scope creep for this already long-running patch.
>
> > CXChoice cannot possibly have many valid values. So how about:
> > ```
> > unsigned char ThreadPriorityBackgroundForIndexing;
> > unsigned char ThreadPriorityBackgroundForEditing;
> > ```
> > Then size_t Size could become unsigned Size and all non-pointer options
> > would fit into 8 bytes on x86_64.
>
> Hmmm that could work, but how about:
> ```
> /* Stores a value of type CXChoice. */
> int ThreadPriorityBackgroundForIndexing : 2;
> /* Stores a value of type CXChoice. */
> int ThreadPriorityBackgroundForEditing : 2;
> ```
> so that they pack together with the existing bit-fields?
>
> > Did you reorder the words in the variable names intentionally?
> > CXGlobalOpt_ThreadBackgroundPriorityForIndexing =>
> > ThreadPriorityBackgroundForIndexing
>
> Nope, sorry for the confusion, that was a think-o on my part.
> I think that would be great, at least for the setter. As you mention, we
> might not want to deprecate the getter (so long as it reports accurate
> information to the caller) because that could be useful still. However, I was
> also thinking that same logic could apply (at least in theory) to other
> options in the structure and so we might want to deprecate it with a
> replacement that gets all of the options from the index at once. However,
> that felt like scope creep for this already long-running patch.
For the time being, only the two global options depend on the environment.
Though one could get the system temporary directory path if
`PreambleStoragePath` is not overridden. Anyway, there is no known use case for
getting such information, so no need to implement this right now, especially
since `clang_CXIndex_getGlobalOptions()` already exists and would work
correctly without modifications.
> > CXChoice cannot possibly have many valid values. So how about:
> > ```
> > unsigned char ThreadPriorityBackgroundForIndexing;
> > unsigned char ThreadPriorityBackgroundForEditing;
> > ```
> > Then size_t Size could become unsigned Size and all non-pointer options
> > would fit into 8 bytes on x86_64.
>
> Hmmm that could work, but how about:
> ```
> /* Stores a value of type CXChoice. */
> int ThreadPriorityBackgroundForIndexing : 2;
> /* Stores a value of type CXChoice. */
> int ThreadPriorityBackgroundForEditing : 2;
> ```
> so that they pack together with the existing bit-fields?
The tighter packing wouldn't reduce the size of the struct further in LLVM 17,
because most likely only one more boolean (`StorePreamblesInMemory`) will be
added to the struct in this release. In future releases the struct size would
have to increase for versioning purposes anyway. But the 2-bitness //would//
reduce the flexibility of `CXChoice`. I have already invented a 4th possible
enumerator. Someone could come up with a fifth in the future. So I'd prefer
`unsigned char` or at least `: 4` (4 bits) for these non-boolean options.
Repository:
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CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D143418/new/
https://reviews.llvm.org/D143418
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