Add Natvis definitions and tests for once_cell types

.github/workflows/ci.yaml

@@ -15,14 +15,32 @@ env:
 jobs:
   test:
     name: Rust
-    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest]
+
+    runs-on: ${{ matrix.os }}
 
     steps:
     - uses: actions/checkout@v2
       with:
         fetch-depth: 0 # fetch tags for publish
 
+    # Install the nightly toolchain when testing on windows
+    - name: Install Rust (nightly)
+      if: matrix.os == 'windows-latest'
+      uses: actions-rs/toolchain@v1
+      with:
+        profile: minimal
+        toolchain: nightly
+        override: true
+
     - run: cargo run -p xtask -- ci
+      if: matrix.os == 'ubuntu-latest'
       env:
         CRATES_IO_TOKEN: ${{ secrets.CRATES_IO_TOKEN }}
         MIRIFLAGS: -Zmiri-strict-provenance
+
+    - name: Test with debugger_visualizer feature
+      run: cargo test --test debugger_visualizer --features debugger_visualizer -- --test-threads=1
+      if: matrix.os == 'windows-latest'

Cargo.toml

@@ -35,6 +35,8 @@ atomic-polyfill = { version = "1", optional = true }
 lazy_static = "1.0.0"
 crossbeam-utils = "0.8.7"
 regex =  "1.2.0"
+debugger_test = "0.1.0"
+debugger_test_parser = "0.1.0"
 
 [features]
 default = ["std"]
@@ -48,6 +50,10 @@ race = []
 # At the moment, this feature is unused.
 unstable = []
 
+# UNSTABLE FEATURES (requires Rust nightly)
+# Enable to use the #[debugger_visualizer] attribute.
+debugger_visualizer = []
+
 parking_lot = ["parking_lot_core"]
 
 [[example]]
@@ -78,5 +84,16 @@ required-features = ["std"]
 name = "test_synchronization"
 required-features = ["std"]
 
+[[test]]
+name = "debugger_visualizer"
+path = "tests/debugger_visualizer.rs"
+required-features = ["debugger_visualizer"]
+# Do not run these tests by default. These tests need to
+# be run with the additional rustc flag `--test-threads=1`
+# since each test causes a debugger to attach to the current
+# test process. If multiple debuggers try to attach at the same
+# time, the test will fail.
+test = false
+
 [package.metadata.docs.rs]
 all-features = true

debug_metadata/README.md

@@ -0,0 +1,111 @@
+## Debugger Visualizers
+
+Many languages and debuggers enable developers to control how a type is
+displayed in a debugger. These are called "debugger visualizations" or "debugger
+views".
+
+The Windows debuggers (WinDbg\CDB) support defining custom debugger visualizations using
+the `Natvis` framework. To use Natvis, developers write XML documents using the natvis
+schema that describe how debugger types should be displayed with the `.natvis` extension.
+(See: https://docs.microsoft.com/en-us/visualstudio/debugger/create-custom-views-of-native-objects?view=vs-2019)
+The Natvis files provide patterns which match type names a description of how to display
+those types.
+
+The Natvis schema can be found either online (See: https://code.visualstudio.com/docs/cpp/natvis#_schema)
+or locally at `<VS Installation Folder>\Xml\Schemas\1033\natvis.xsd`.
+
+The GNU debugger (GDB) supports defining custom debugger views using Pretty Printers.
+Pretty printers are written as python scripts that describe how a type should be displayed
+when loaded up in GDB/LLDB. (See: https://sourceware.org/gdb/onlinedocs/gdb/Pretty-Printing.html#Pretty-Printing)
+The pretty printers provide patterns, which match type names, and for matching
+types, descibe how to display those types. (For writing a pretty printer, see: https://sourceware.org/gdb/onlinedocs/gdb/Writing-a-Pretty_002dPrinter.html#Writing-a-Pretty_002dPrinter).
+
+### Embedding Visualizers
+
+Through the use of the currently unstable `#[debugger_visualizer]` attribute, the `once_cell`
+crate can embed debugger visualizers into the crate metadata.
+
+Currently the two types of visualizers supported are Natvis and Pretty printers.
+
+For Natvis files, when linking an executable with a crate that includes Natvis files,
+the MSVC linker will embed the contents of all Natvis files into the generated `PDB`.
+
+For pretty printers, the compiler will encode the contents of the pretty printer
+in the `.debug_gdb_scripts` section of the `ELF` generated.
+
+### Testing Visualizers
+
+The `once_cell` crate supports testing debugger visualizers defined for this crate. The entry point for
+these tests are `tests/debugger_visualizer.rs`. These tests are defined using the `debugger_test` and
+`debugger_test_parser` crates. The `debugger_test` crate is a proc macro crate which defines a
+single proc macro attribute, `#[debugger_test]`. For more detailed information about this crate,
+see https://crates.io/crates/debugger_test. The CI pipeline for the `once_cell` crate has been updated
+to run the debugger visualizer tests to ensure debugger visualizers do not become broken/stale.
+
+The `#[debugger_test]` proc macro attribute may only be used on test functions and will run the
+function under the debugger specified by the `debugger` meta item.
+
+This proc macro attribute has 3 required values:
+
+1. The first required meta item, `debugger`, takes a string value which specifies the debugger to launch.
+2. The second required meta item, `commands`, takes a string of new line (`\n`) separated list of debugger
+commands to run.
+3. The third required meta item, `expected_statements`, takes a string of new line (`\n`) separated list of
+statements that must exist in the debugger output. Pattern matching through regular expressions is also
+supported by using the `pattern:` prefix for each expected statement.
+
+#### Example:
+
+```rust
+#[debugger_test(
+    debugger = "cdb",
+    commands = "command1\ncommand2\ncommand3",
+    expected_statements = "statement1\nstatement2\nstatement3")]
+fn test() {
+
+}
+```
+
+Using a multiline string is also supported, with a single debugger command/expected statement per line:
+
+```rust
+#[debugger_test(
+    debugger = "cdb",
+    commands = "
+command1
+command2
+command3",
+    expected_statements = "
+statement1
+pattern:statement[0-9]+
+statement3")]
+fn test() {
+
+}
+```
+
+In the example above, the second expected statement uses pattern matching through a regular expression
+by using the `pattern:` prefix.
+
+#### Testing Locally
+
+Currently, only Natvis visualizations have been defined for the `once_cell` crate via `debug_metadata/once_cell.natvis`,
+which means the `tests/debugger_visualizer.rs` tests need to be run on Windows using the `*-pc-windows-msvc` targets.
+To run these tests locally, first ensure the debugging tools for Windows are installed or install them following
+the steps listed here, [Debugging Tools for Windows](https://docs.microsoft.com/en-us/windows-hardware/drivers/debugger/).
+Once the debugging tools have been installed, the tests can be run in the same manner as they are in the CI
+pipeline.
+
+#### Note
+
+When running the debugger visualizer tests, `tests/debugger_visualizer.rs`, they need to be run consecutively
+and not in parallel. This can be achieved by passing the flag `--test-threads=1` to rustc. This is due to
+how the debugger tests are run. Each test marked with the `#[debugger_test]` attribute launches a debugger
+and attaches it to the current test process. If tests are running in parallel, the test will try to attach
+a debugger to the current process which may already have a debugger attached causing the test to fail.
+
+For example:
+
+```
+cargo test --test debugger_visualizer --features debugger_visualizer -- --test-threads=1
+```

debug_metadata/once_cell.natvis

@@ -0,0 +1,53 @@
+<?xml version="1.0" encoding="utf-8"?>
+<AutoVisualizer xmlns="http://schemas.microsoft.com/vstudio/debugger/natvis/2010">
+  <Type Name="once_cell::imp::OnceCell&lt;*&gt;">
+    <DisplayString>{value}</DisplayString>
+    <Expand>
+      <Item Name="[queue]">queue</Item>
+      <Item Name="[marker]">_marker</Item>
+      <Item Name="[value]">value</Item>
+    </Expand>
+  </Type>
+
+  <Type Name="once_cell::race::OnceBool">
+    <DisplayString>{inner.inner.v.value == 1}</DisplayString>
+  </Type>
+
+  <Type Name="once_cell::race::once_box::OnceBox&lt;*&gt;">
+    <Expand>
+      <ExpandedItem>inner.p</ExpandedItem>
+    </Expand>
+  </Type>
+
+  <Type Name="once_cell::race::OnceNonZeroUsize">
+    <Expand>
+      <ExpandedItem>inner</ExpandedItem>
+    </Expand>
+  </Type>
+
+  <Type Name="once_cell::sync::Lazy&lt;*&gt;">
+    <Expand>
+      <ExpandedItem>cell</ExpandedItem>
+      <Item Name="[init]">init</Item>
+    </Expand>
+  </Type>
+
+  <Type Name="once_cell::sync::OnceCell&lt;*&gt;">
+    <Expand>
+      <ExpandedItem>__0</ExpandedItem>
+    </Expand>
+  </Type>
+
+  <Type Name="once_cell::unsync::Lazy&lt;*&gt;">
+    <Expand>
+      <ExpandedItem>cell</ExpandedItem>
+      <Item Name="[init]">init</Item>
+    </Expand>
+  </Type>
+
+  <Type Name="once_cell::unsync::OnceCell&lt;*&gt;">
+    <Expand>
+      <ExpandedItem>inner</ExpandedItem>
+    </Expand>
+  </Type>
+</AutoVisualizer>

src/lib.rs

@@ -328,6 +328,11 @@
 //! See the [tracking issue](https://github.com/rust-lang/rust/issues/74465).
 
 #![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(
+    feature = "debugger_visualizer",
+    feature(debugger_visualizer),
+    debugger_visualizer(natvis_file = "../debug_metadata/once_cell.natvis")
+)]
 
 #[cfg(feature = "alloc")]
 extern crate alloc;