Add stream_to_parser_with_base_dir

[topecongiro]

This PR adds stream_to_parser_with_base_dir, which creates a parser from a token stream and a base directory.

Context: I would like to parse cfg_if! macro and get a list of modules defined inside it from rustfmt so that rustfmt can format those modules (cc rust-lang/rustfmt#3253). To do so, I need to create a parser from TokenStream and set the directory of Parser to the same directory as the parent directory of a file which contains cfg_if! invocation. AFAIK there is no way to achieve this, and hence this PR.

Alternatively, I could change the visibility of Parser.directory from crate to pub so that the value can be modified after initializing a parser. I don't have a preference over either approach (or others, as long as it works).

[rust-highfive]

r? @michaelwoerister

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[michaelwoerister]

Thanks, @topecongiro! If you add an explanation of the rationale/use-case for the function to the doc comment, I'm fine with adding it.

[topecongiro]

Thanks for the review, I added the doc comment in b07dbe1.

[michaelwoerister]

@bors r+

[bors]

📌 Commit b07dbe1 has been approved by michaelwoerister

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

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travis_time:end:01461648:start=1558447218876114621,finish=1558447309219498007,duration=90343383386
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
$ export AWS_ACCESS_KEY_ID=AKIA46X5W6CZEJZ6XT55
---
[00:04:05] tidy error: /checkout/src/libsyntax/parse/mod.rs:337: trailing whitespace
[00:04:11] some tidy checks failed
[00:04:11] 
[00:04:11] 
[00:04:11] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:04:11] 
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[00:04:11] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:04:11] Build completed unsuccessfully in 0:01:13
[00:04:11] Build completed unsuccessfully in 0:01:13
[00:04:11] make: *** [tidy] Error 1
[00:04:11] Makefile:67: recipe for target 'tidy' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:231a833f
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Tue May 21 14:06:09 UTC 2019
---
travis_time:end:28935966:start=1558447570716415794,finish=1558447570721734446,duration=5318652
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travis_time:start:0bd8ea72
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
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travis_time:start:08fd1726
travis_time:start:08fd1726
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
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travis_time:start:00b66475
$ dmesg | grep -i kill

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)

[topecongiro]

Oops, sorry, forgot to run the tidy check... fixed it in 1f1a917.

[michaelwoerister]

@bors r+

[bors]

📌 Commit 1f1a917 has been approved by michaelwoerister