Fix the MSRV issue on v0.2.13

Author: 38

.github/workflows/push-check.yml

@@ -3,6 +3,20 @@ name: Push Check
 on: [push]
 
 jobs:
+  msrv:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+      with:
+          submodules: recursive
+    - uses: actions-rs/toolchain@v1
+      with:
+          toolchain: 1.36.0
+          override: true
+    - uses: actions-rs/cargo@v1
+      with:
+          command: test
+          args: --verbose --all-features
   build_and_test:
     runs-on: ${{ matrix.os }}
     strategy:

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changelog
 
+## Plotters latest (?)
+### Fixed
+
+- Compile error with older rustc which causing breaks
+
 ## Plotters 0.2.13 (2020-05-04)
 ### Added
 

CONTRIBUTING.md

@@ -105,6 +105,11 @@ cargo test --lib --target wasm32-unknown-unknown
 
 For the debugging you could set the `NO_HEADLESS=1` environment variable to run the tests using the local server instead of the headless browser.
 
+### Minimal Supported Compiler Version
+
+Currently we should make sure Plotters is compatible with rustc 1.36.0.
+Before making a PR, please check if the code compile with 1.36.0
+
 ### Code Coverage
 
 For for the code coverage information you may want to use [cargo-tarpaulin](https://crates.io/crates/cargo-tarpaulin). Please note that it works with x86_64 GNU/Linux only, and the doc tests coverage require nightly Rust.
@@ -122,3 +127,5 @@ Usage:
 cargo tarpaulin --all-features --run-types Tests Doctests -o Xml --output-dir target/test
 pycobertura show target/test/cobertura.xml
 ```
+
+

doc-template/msrv.txt

@@ -0,0 +1 @@
+1.36.0

publish.sh

@@ -34,6 +34,12 @@ git add -u .
 git commit -m "Bump version number from ${OLD_VERSION} to ${NEW_VERSION}"
 git tag -a "v${NEW_VERSION}" -m "Plotters ${NEW_VERSION} release"
 
+# Verify MSRV
+rustup install $(cat ${ROOT}/doc-template/msrv.txt)
+rustup default $(cat ${ROOT}/doc-template/msrv.txt)
+cargo build
+rustup default stable
+
 cargo publish
 git push origin
 git push origin "v${NEW_VERSION}"

src/chart/context.rs

@@ -29,7 +29,7 @@ pub struct SeriesAnno<'a, DB: DrawingBackend> {
 
 impl<'a, DB: DrawingBackend> SeriesAnno<'a, DB> {
     pub(crate) fn get_label(&self) -> &str {
-        self.label.as_deref().map(|x| x).unwrap_or("")
+        self.label.as_ref().map(|x| x.as_str()).unwrap_or("")
     }
 
     pub(crate) fn get_draw_func(