The flang-new driver doesn't check for the case of the parser failing to
consume the entire input file. This is of course never an ideal outcome,
and usually signals a need to improve error recovery, but it is better
for the compiler to admit failure rather than to silently proceed with
compilation of what may well be an incomplete parse tree.

Fortran INCLUDE lines have (until now) been treated like #include
directives. This isn't how things work with other Fortran compilers when
running under the -E option for preprocessing only, so stop doing it by
default, and add -fpreprocess-include-lines to turn it back on when
desired.

Module files emitted by this Fortran compiler are valid Fortran source
files. Symbols that are USE-associated into modules are represented in
their module files with USE statements and special comments with hash
codes in them to ensure that those USE statements resolve to the same
modules that were used to build the module when its module file was
generated.

This scheme prevents unchecked module file growth in large applications
by not emitting USE-associated symbols redundantly. This problem can be
especially bad when derived type definitions must be repeated in the
module files of their clients, and the clients of those modules, and so
on. However, this scheme has the disadvantage that clients of modules
must be compiled with dependent modules in the module search path.

This new -fhermetic-module-files option causes module file output to be
free of dependences on any non-intrinsic module files; dependent modules
are instead emitted as part of the module file, rather than being
USE-associated. It is intended for top level library module files that
are shipped with binary libraries when it is not convenient to collect
and ship their dependent module files as well.

Fixes https://github.com/llvm/llvm-project/issues/97398.

When there are one or more fatal error messages produced by the parser,
semantic analysis is not performed. But when there are messages produced
by the parser and none of them are fatal, those messages are emitted to
the user before compilation continues with semantic analysis, and any
messages produced by semantics are emitted after the messages from
parsing.

This can be confusing for the user, as the messages may no longer all be
in source file location order. It also makes it difficult to write tests
that check for both non-fatal messages from parsing as well as messages
from semantics using inline CHECK: or other expected messages in test
source code.

This patch ensures that if semantic analysis is performed, and non-fatal
messages were produced by the parser, that all the messages will be
combined and emitted in source file order.

Flang driver was already able to enable the CUDA language feature base
on the file extension but there was no command line option. This PR adds
one.

Moves the defintion of `SemanticsContext` within the Flang driver.

Rather than in `CompilerInvocation`, semantic context fits better within
`CompilerInstance` that encapsulates the objects that are required to
run the
frontend. `CompilerInvocation` is better suited for objects
encapsulating compiler configuration (e.g. set-up resulting from user
input or host set-up).

Begin upstreaming of CUDA Fortran support in LLVM Flang.

This first patch implements parsing for CUDA Fortran syntax,
including:
 - a new LanguageFeature enum value for CUDA Fortran
 - driver change to enable that feature for *.cuf and *.CUF source files
 - parse tree representation of CUDA Fortran syntax
 - dumping and unparsing of the parse tree
 - the actual parsers for CUDA Fortran syntax
 - prescanning support for !@CUF and !$CUF
 - basic sanity testing via unparsing and parse tree dumps

... along with any minimized changes elsewhere to make these
work, mostly no-op cases in common::visitors instances in
semantics and lowering to allow them to compile in the face
of new types in variant<> instances in the parse tree.

Because CUDA Fortran allows the kernel launch chevron syntax
("call foo<<<blocks, threads>>>()") only on CALL statements and
not on function references, the parse tree nodes for CallStmt,
FunctionReference, and their shared Call were rearranged a bit;
this caused a fair amount of one-line changes in many files.

More patches will follow that implement CUDA Fortran in the symbol
table and name resolution, and then semantic checking.

Differential Revision: https://reviews.llvm.org/D150159

in order to provide as much information as possible to the user. The
diagnostic will now look like for example:

  error: error reading '/tmp/foo.c': Permission denied

(This addresses a FIXME from 2019, 9ef6c49baf45)

Differential revision: https://reviews.llvm.org/D146280

This patch re-factors the driver code in LLVM Flang (frontend +
compiler) to use the MLIR style. For more context, please see:
https://discourse.llvm.org/t/rfc-coding-style-in-the-driver/

Most changes here are rather self-explanatory. Accessors are renamed to
be more consistent with the rest of LLVM (e.g. allSource -->
getAllSources). Additionally, MLIR clang-tidy files are added in the
affected directories.

clang-tidy and clang-format files were copied from MLIR. Small
additional changes are made to silence clang-tidy/clang-format
warnings.

[1] https://mlir.llvm.org/getting_started/DeveloperGuide/

Differential Revision: https://reviews.llvm.org/D125007

This patch basically implements [1] in ExecuteCompilerInvocation.cpp. It
also:
  * replaces `CreateFrontendBaseAction` with `CreateFrontendAction`
    (only one method is needed ATM, this change removes the extra
    indirection)
  * removes `InvalidAction` from the `ActionKind` enum (I don't think it
    adds much and keeping it would mean adding a new void case in
    `CreateFrontendAction`)
  * sets the default frontend action in FrontendOptions.h to
    `ParseSyntaxOnly` (note that this is still overridden independently
    in `ParseFrontendArg` in CompilerInvocation.cpp)

No new functionality is added, hence no tests.

[1] https://llvm.org/docs/CodingStandards.html#don-t-use-default-labels-in-fully-covered-switches-over-enumerations

Differential Revision: https://reviews.llvm.org/D124245