[Bug other/107634] Very long filenames and URLs for sphinx-based docs

["marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107634

--- Comment #8 from Martin Liška <marxin at gcc dot gnu.org> ---
About the number of files. Yes, that's the biggest change when it comes to
Sphinx and I see it also as a drawback. However, it's the only valid file
naming scheme supported by Sphinx and there are projects with non-trivial docs
where the average size of a file matches to what we have:

gcc manual:

TOTAL files: 312
Total LOC: 68643
Average LOC: 220
Median LOC: 104

linux kernel:

TOTAL files: 3198
Total LOC: 649105
Average LOC: 202
Median LOC: 485

godot game engine:

=== TOTAL files: 1262
Total LOC: 308497
Average LOC: 244
Median LOC: 325

coreboot:

=== TOTAL files: 354
Total LOC: 36916
Average LOC: 104
Median LOC: 139

Note the GCC manual contains many target-specific sections and I don't believe
they should be presented at a single HTML page:

extensions-to-the-c-language-family/declaring-attributes-of-functions/ - 35
files
extensions-to-the-c-language-family/target-builtins/ - 36 files
gcc-command-options/machine-dependent-options/ - 62 files

Where I can imagine merging the files are following sub-folders:

extensions-to-the-c++-language/backwards-compatibility.rst [27]
extensions-to-the-c++-language/c++-concepts.rst [44]
extensions-to-the-c++-language/c++-interface-and-implementation-pragmas.rst
[97]
extensions-to-the-c++-language/c++-specific-variable-function-and-type-attributes.rst
[95]
extensions-to-the-c++-language/deprecated-features.rst [43]
extensions-to-the-c++-language/extracting-the-function-pointer-from-a-bound-pointer-to-member-function.rst
[48]
extensions-to-the-c++-language/function-multiversioning.rst [65]
extensions-to-the-c++-language/restricting-pointer-aliasing.rst [52]
extensions-to-the-c++-language/type-traits.rst [165]
extensions-to-the-c++-language/vague-linkage.rst [80]
extensions-to-the-c++-language/when-is-a-volatile-c++-object-accessed.rst [58]
extensions-to-the-c++-language/wheres-the-template.rst [131]
./extensions-to-the-c++-language.rst [34]

c-implementation-defined-behavior/architecture.rst [47]
c-implementation-defined-behavior/arrays-and-pointers.rst [46]
c-implementation-defined-behavior/characters.rst [93]
c-implementation-defined-behavior/declarators.rst [14]
c-implementation-defined-behavior/environment.rst [18]
c-implementation-defined-behavior/floating-point.rst [88]
c-implementation-defined-behavior/hints.rst [35]
c-implementation-defined-behavior/identifiers.rst [28]
c-implementation-defined-behavior/integers.rst [66]
c-implementation-defined-behavior/library-functions.rst [19]
c-implementation-defined-behavior/locale-specific-behavior.rst [12]
c-implementation-defined-behavior/preprocessing-directives.rst [54]
c-implementation-defined-behavior/qualifiers.rst [53]
c-implementation-defined-behavior/statements.rst [14]
c-implementation-defined-behavior/structures-unions-enumerations-and-bit-fields.rst
[78]
c-implementation-defined-behavior/translation.rst [20]
./c-implementation-defined-behavior.rst [46]

gnu-objective-c-features/compatibilityalias.rst [26]
gnu-objective-c-features/constant-string-objects.rst [64]
gnu-objective-c-features/exceptions.rst [79]
gnu-objective-c-features/fast-enumeration.rst [221]
gnu-objective-c-features/garbage-collection.rst [81]
gnu-objective-c-features/gnu-objective-c-runtime-api.rst [98]
gnu-objective-c-features/load-executing-code-before-main.rst [141]
gnu-objective-c-features/messaging-with-the-gnu-objective-c-runtime.rst [145]
gnu-objective-c-features/synchronization.rst [36]
gnu-objective-c-features/type-encoding.rst [280]

known-causes-of-trouble-with-gcc/actual-bugs-we-havent-fixed-yet.rst [14]
known-causes-of-trouble-with-gcc/certain-changes-we-dont-want-to-make.rst [236]
known-causes-of-trouble-with-gcc/common-misunderstandings-with-gnu-c.rst [296]
known-causes-of-trouble-with-gcc/disappointments-and-misunderstandings.rst
[102]
known-causes-of-trouble-with-gcc/fixed-header-files.rst [39]
known-causes-of-trouble-with-gcc/incompatibilities-of-gcc.rst [233]
known-causes-of-trouble-with-gcc/interoperation.rst [153]
known-causes-of-trouble-with-gcc/standard-libraries.rst [33]
known-causes-of-trouble-with-gcc/warning-messages-and-error-messages.rst [46]

language-standards-supported-by-gcc/c++-language.rst [71]
language-standards-supported-by-gcc/c-language.rst [139]
language-standards-supported-by-gcc/d-language.rst [11]
language-standards-supported-by-gcc/go-language.rst [10]
language-standards-supported-by-gcc/objective-c-and-objective-c++-languages.rst
[62]
language-standards-supported-by-gcc/references-for-other-languages.rst [13]

That's a reduction of ~50 files. To be honest, the split is mandatory thing and
there's not much I can do about it.

Just a note for the old .texi files: we used to have files
(./gcc/doc/invoke.texi ./gcc/doc/extend.texi, ./gcc/fortran/intrinsic.texi)
that tend to have 1000s of lines which is not ideal either.