executor: add TypedExecutor (#993)

Adds a `TypedExecutor` trait that describes how to spawn futures of a specific
type. This is useful for implementing functions that are generic over an executor
and wish to support both `Send` and `!Send` cases.

ci/azure-patch-crates.yml

@@ -0,0 +1,16 @@
+steps:
+  - script: |
+      set -e
+
+      # Remove any existing patch statements
+      mv Cargo.toml Cargo.toml.bck
+      sed -n '/\[patch.crates-io\]/q;p' Cargo.toml.bck > Cargo.toml
+
+      # Patch all crates
+      cat ci/patch.toml >> Cargo.toml
+
+      # Print `Cargo.toml` for debugging
+      echo "~~~~ Cargo.toml ~~~~"
+      cat Cargo.toml
+      echo "~~~~~~~~~~~~~~~~~~~~"
+    displayName: Patch Cargo.toml

ci/azure-test-stable.yml

@@ -27,13 +27,7 @@ jobs:
       displayName: cargo test -p ${{ crate }}
       workingDirectory: $(Build.SourcesDirectory)/${{ crate }}
 
-  - script: |
-      set -e
-      cat ci/patch.toml >> Cargo.toml
-      echo "~~~~ Cargo.toml ~~~~"
-      cat Cargo.toml
-      echo "~~~~~~~~~~~~~~~~~~~~"
-    displayName: Patch Cargo.toml
+  - template: azure-patch-crates.yml
 
   - ${{ each crate in parameters.crates }}:
     - script: cargo test

ci/azure-tsan.yml

@@ -14,14 +14,10 @@ jobs:
     parameters:
       rust_version: nightly-2018-11-18
 
+  - template: azure-patch-crates.yml
   - script: |
         set -e
 
-        cat ci/patch.toml >> Cargo.toml
-        echo "~~~~ Cargo.toml ~~~~"
-        cat Cargo.toml
-        echo "~~~~~~~~~~~~~~~~~~~~"
-
         # Make sure the benchmarks compile
         export ASAN_OPTIONS="detect_odr_violation=0 detect_leaks=0"
         export TSAN_OPTIONS="suppressions=`pwd`/ci/tsan"