Enhanced hover tooltips

Hover tooltips now extract documentation and declarations from
source based on the the file and span information that comes out
of the save-analysis. If the save-analysis data is missing (i.e.
there is no `Def` available), racer is used as fallback and the
`Def` is sythesized from the racer `Match` if one is found.

Function and object declarations are formatted using rustfmt and
context for local variables is also included in the tooltips.

All documentation that is discovered is now post-processed in order
to clean up code blocks so that syntax coloring works in in editors
that support markdown.

The racer fallback can be disabled via the `racer_completion`
configuration flag.

.travis.yml

@@ -11,14 +11,13 @@ os:
 - osx
 rust:
 - nightly
-install:
+install: |
     # Required for Racer autoconfiguration
     rustup component add rust-src
+    rustup component add rust-analysis
 script: |
   #!/bin/bash
   set -e
-
   cargo build -v
   cargo test -v
-
   set +e

README.md

@@ -114,7 +114,8 @@ Currently we accept the following options:
 * `no_default_features` (`bool`, defaults to `false`) disables default Cargo
   features
 * `racer_completion` (`bool`, defaults to `true`) enables code completion using
-  racer (which is, at the moment, our only code completion backend)
+  racer (which is, at the moment, our only code completion backend). Also enables
+  hover tooltips to fall back to racer when save-analysis data is unavailable.
 * `clippy_preference` (`String`, defaults to `"opt-in"`) controls eagerness of clippy
   diagnostics when available. Valid values are _(case-insensitive)_:
   - `"off"` Disable clippy lints.
@@ -131,6 +132,14 @@ and the following unstable options:
 * `cfg_test` (`bool`, defaults to `false`) checks the project as if you were
   running `cargo test` rather than `cargo build`. I.e., compiles (but does not
   run) test code.
+* `full_docs` (`bool`, defaults to `false`) instructs rustc to populate the
+  save-analysis data with full source documentation. When set to `false`, only the
+  first paragraph is recorded. This option _currently_ has little to no effect on
+  hover tooltips. The save-analysis docs are only used if source extraction fails.
+  This option has no effect on the standard library.
+* `show_hover_context` show additional context in hover tooltips when available.
+  This is often the local variable declaration. When set to false the content is
+  only availabe when holding the `ctrl` key in some editors.
 
 
 ## Troubleshooting

appveyor.yml

@@ -22,6 +22,7 @@ install:
   - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
   # Required for Racer autoconfiguration
   - rustup component add rust-src
+  - rustup component add rust-analysis
   # Print version info
   - rustc -Vv
   - cargo -V