resolve: Populate external modules in more automatic and lazy way

[petrochenkov]

So, resolve had this function populate_module_if_necessary for loading module children from other crates from metadata.
I never really understood when it should've been called and when not.
This PR removes the function and loads the module children automatically on the first access instead.

r? @eddyb

[petrochenkov]

@bors try

[bors]

⌛ Trying commit 2245577 with merge ac89e03...

[petrochenkov]

Hmm, no notification, but looks like the build completed successfully.
@rust-timer build ac89e03

[rust-timer]

Success: Queued ac89e03 with parent f690098, comparison URL.

[rust-timer]

Finished benchmarking try commit ac89e03, comparison URL.

[petrochenkov]

Ok, perf looks mostly like a noise, but the change still makes sense logically.

[wirelessringo]

Ping from triage. @eddyb any updates on this? Thanks.

[eddyb]

@bors r+

[bors]

📌 Commit cbaf397804be470b1fec12c5bfe0c7edcd923199 has been approved by eddyb

[bors]

⌛ Testing commit cbaf397804be470b1fec12c5bfe0c7edcd923199 with merge 047f9faa888b1117a85cbce106d866273c80008a...

[bors]

💔 Test failed - checks-azure

[rust-highfive]

The job mingw-check of your PR failed (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

2019-08-09T18:46:29.5461739Z do so (now or later) by using -b with the checkout command again. Example:
2019-08-09T18:46:29.5461926Z 
2019-08-09T18:46:29.5462310Z   git checkout -b <new-branch-name>
2019-08-09T18:46:29.5462511Z 
2019-08-09T18:46:29.5462941Z HEAD is now at 047f9faa8 Auto merge of #63149 - petrochenkov:lazypop2, r=eddyb
2019-08-09T18:46:29.5629402Z ##[section]Starting: Collect CPU-usage statistics in the background
2019-08-09T18:46:29.5632337Z ==============================================================================
2019-08-09T18:46:29.5632443Z Task         : Bash
2019-08-09T18:46:29.5632525Z Description  : Run a Bash script on macOS, Linux, or Windows
---
2019-08-09T18:54:39.9359151Z     Checking rustc_ast_borrowck v0.0.0 (/checkout/src/librustc_ast_borrowck)
2019-08-09T18:54:41.1093100Z     Checking rustc_codegen_utils v0.0.0 (/checkout/src/librustc_codegen_utils)
2019-08-09T18:54:41.6917094Z     Checking rustc_plugin v0.0.0 (/checkout/src/librustc_plugin)
2019-08-09T18:54:41.9702335Z     Checking rustc_resolve v0.0.0 (/checkout/src/librustc_resolve)
2019-08-09T18:54:43.2198530Z error[E0599]: no variant or associated item named `AssocExistential` found for type `rustc::hir::def::DefKind` in the current scope
2019-08-09T18:54:43.2204323Z    --> src/librustc_resolve/build_reduced_graph.rs:665:33
2019-08-09T18:54:43.2210247Z     |
2019-08-09T18:54:43.2211591Z 665 |             | Res::Def(DefKind::AssocExistential, _)
2019-08-09T18:54:43.2217825Z     |                                 ^^^^^^^^^^^^^^^^ variant or associated item not found in `rustc::hir::def::DefKind`
2019-08-09T18:54:43.4002363Z error: aborting due to previous error
2019-08-09T18:54:43.4002501Z 
2019-08-09T18:54:43.4003124Z For more information about this error, try `rustc --explain E0599`.
2019-08-09T18:54:43.4188001Z error: Could not compile `rustc_resolve`.
2019-08-09T18:54:43.4188001Z error: Could not compile `rustc_resolve`.
2019-08-09T18:54:43.4188400Z warning: build failed, waiting for other jobs to finish...
2019-08-09T18:54:53.7419786Z error: build failed
2019-08-09T18:54:53.7446416Z command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "check" "--target" "x86_64-unknown-linux-gnu" "-j" "2" "--release" "--color" "always" "--features" "" "--manifest-path" "/checkout/src/rustc/Cargo.toml" "--message-format" "json"
2019-08-09T18:54:53.7447144Z expected success, got: exit code: 101
2019-08-09T18:54:53.7456765Z failed to run: /checkout/obj/build/bootstrap/debug/bootstrap check
2019-08-09T18:54:53.7457172Z Build completed unsuccessfully in 0:05:36
2019-08-09T18:54:55.0424325Z ##[error]Bash exited with code '1'.
2019-08-09T18:54:55.0455823Z ##[section]Starting: Upload CPU usage statistics
2019-08-09T18:54:55.0458957Z ==============================================================================
2019-08-09T18:54:55.0459055Z Task         : Bash
2019-08-09T18:54:55.0459430Z Description  : Run a Bash script on macOS, Linux, or Windows

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[petrochenkov]

@bors r=eddyb

[bors]

📌 Commit 2cb9207 has been approved by eddyb

[petrochenkov]

No, not a rebase, the previous error was the same.
Looks like either randomly changing or platform-dependent diagnostics.

[Mark-Simulacrum]

(To be clear, I'm not positive that this PR was the cause of that failure, it's just my best guess. Feel free to re-r+ if you feel confident).

[bors]

☔ The latest upstream changes (presumably #63489) made this pull request unmergeable. Please resolve the merge conflicts.

[petrochenkov]

Span changes causing issues with diagnostics reproducibility are backed out.

@bors r=eddyb

[bors]

📌 Commit 4331bf51c440d1d8a862d0777a0984ecf488851c has been approved by eddyb

[bors]

☔ The latest upstream changes (presumably #63627) made this pull request unmergeable. Please resolve the merge conflicts.

[petrochenkov]

@bors r=eddyb

[bors]

📌 Commit 5e47cd4 has been approved by eddyb