Isn't the situation exactly the same if the 'import's are replaced with '#include's?

-- Gaby

| -----Original Message-----
| From: Modules <modules-bounces_at_[hidden]cpp.org> On Behalf Of Nathan
| Sidwell
| Sent: Wednesday, March 6, 2019 1:01 PM
| To: modules_at_[hidden]; Mathias Stearn
| <redbeard0531+isocpp_at_[hidden]>
| Cc: boris_at_codesynthesis.com; brad.king_at_kitware.com; WG21 Tooling Study
| Group SG15 <tooling_at_[hidden]>; Ben Boeckel
| <ben.boeckel_at_[hidden]>
| Subject: Re: [isocpp-modules] [Tooling] Dependency information for module-
| aware build tools
|
| On 3/6/19 3:01 PM, Mathias Stearn wrote:
| >
| >
| > On Wed, Mar 6, 2019 at 10:18 AM Nathan Sidwell <nathan_at_acm.org
| > <mailto:nathan_at_[hidden]>> wrote:
| >
| > Yes, a BMI is required for a header import. Textually including the
| > header import's original header file is not equivalent.
| >
| >
| > It won't be required for the scan stage will it? If it is, there is a
| > bootstrapping problem because there is no good way to figure out which
| > order to build the header-unit BMIs in if they import other
| > header-units. I've been assuming that the scan stage will be able to
| > just temporarily mask off the defines and replace them with the correct
| > ones for the header-unit while scanning a file, so that scanning has no
| > generated dependencies.
|
| As header units export #defines, which can go on to determine the path
| of conditional inclusion, you have to decide:
|
| a) if you want precise scanning, you need the header units at scan time
|
| b) if you're ok with imprecise scanning (getting false positives). But
| you need something other than the C++ preprocessor[*]. Of course you
| have to deal with things like:
|
| import "config";
| #if MACRO_MAYBE_FROM_IMPORT
| import linux;
| #else
| import windows;
| #endif
|
| Only one of those imports is needed and (very likely) building the
| unneeded one will fail. So you build both, but don't abort the build
| until a true dependency needs a failed module.
|
| nathan
|
| [*] make some assumptions (define some requirements) about code
| formatting and recursively execute;
| grep import -> import list
| grep '#include' -> includes to recursively process
|
| --
| Nathan Sidwell
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