Add option to continue if an Error occurs in one section (#128)

* Collect and emit cargo:warnings.

* Optionally continue if Build block failed.

* Optionally continue if Git block failed.

* Optionally continue if Sysinfo block failed.

* Optionally continue if Rustc block failed.

* Add test for Git skip_if_error

  - This test needs a directory that is not a git repository or
    a subdirectory of a git repository.
  - Use a temporary directory, provided by the tempfile crate.
  - The tempfile dependency is only needed for this one test. It is only
    compiled in the test configuration and if the git feature is active.
    Sadly, there is no way to define optional dev-dependencies[0], so
    deactivate the unused_crate_dependencies lint to allow compilation
    of the other features.

  [0]: rust-lang/cargo#1596

* Add docs for skip_if_error.

* Fix typos

* Fix mistake in docs.

If the "git" feature is not active, no git2 Errors will be generated.

Cargo.toml

@@ -44,4 +44,5 @@ rustversion = "1"
 lazy_static = "1"
 regex = "1"
 serial_test = "0"
+tempfile = "3"
 

src/config.rs

@@ -283,6 +283,7 @@ pub(crate) struct Config {
     cfg_map: BTreeMap<VergenKey, Option<String>>,
     head_path: Option<PathBuf>,
     ref_path: Option<PathBuf>,
+    warnings: Vec<String>,
 }
 
 impl Default for Config {
@@ -296,6 +297,7 @@ impl Default for Config {
                 .collect(),
             head_path: Option::default(),
             ref_path: Option::default(),
+            warnings: Vec::new(),
         }
     }
 }
@@ -319,6 +321,7 @@ mod test {
         assert_eq!(*config.timezone(), TimeZone::Utc);
         assert_eq!(*config.kind(), TimestampKind::Timestamp);
         assert!(config.semver());
+        assert!(!config.skip_if_error());
     }
 
     #[cfg(not(feature = "build"))]
@@ -353,6 +356,7 @@ mod test {
         assert_eq!(*config.semver_kind(), SemverKind::Normal);
         assert!(config.sha());
         assert_eq!(*config.sha_kind(), ShaKind::Normal);
+        assert!(!config.skip_if_error());
     }
 
     #[cfg(not(feature = "git"))]
@@ -367,6 +371,7 @@ mod test {
         assert!(config.host_triple());
         assert!(config.llvm_version());
         assert!(config.sha());
+        assert!(!config.skip_if_error());
     }
 
     #[cfg(not(feature = "rustc"))]
@@ -382,6 +387,7 @@ mod test {
         assert!(config.memory());
         assert!(config.cpu_vendor());
         assert!(config.cpu_core_count());
+        assert!(!config.skip_if_error());
     }
 
     #[cfg(not(feature = "si"))]

src/feature/build.rs

@@ -37,6 +37,8 @@ use {
 /// * If the `semver` field is false, the semver instruction will not be generated.
 /// * **NOTE** - By default, the date/time related instructions will use [`UTC`](TimeZone::Utc).
 /// * **NOTE** - The date/time instruction output is determined by the [`kind`](TimestampKind) field and can be any combination of the three.
+/// * **NOTE** - To keep processing other sections if an Error occurs in this one, set
+///     [`Build::skip_if_error`](Build::skip_if_error_mut()) to true.
 ///
 /// # Example
 ///
@@ -89,6 +91,9 @@ pub struct Build {
     kind: TimestampKind,
     /// Enable/Disable the `VERGEN_BUILD_SEMVER` instruction.
     semver: bool,
+    /// Enable/Disable skipping [`Build`] if an Error occurs.
+    /// Use [`option_env!`](std::option_env!) to read the generated environment variables.
+    skip_if_error: bool,
 }
 
 #[cfg(feature = "build")]
@@ -100,6 +105,7 @@ impl Default for Build {
             timezone: TimeZone::Utc,
             kind: TimestampKind::Timestamp,
             semver: true,
+            skip_if_error: false,
         }
     }
 }
@@ -115,7 +121,7 @@ impl Build {
 pub(crate) fn configure_build(instructions: &Instructions, config: &mut Config) -> Result<()> {
     let build_config = instructions.build();
 
-    if build_config.has_enabled() {
+    let mut add_entries = || {
         if *build_config.timestamp() {
             match build_config.timezone() {
                 TimeZone::Utc => {
@@ -135,8 +141,28 @@ pub(crate) fn configure_build(instructions: &Instructions, config: &mut Config)
                 env::var("CARGO_PKG_VERSION").ok(),
             );
         }
+        Ok(())
+    };
+
+    if build_config.has_enabled() {
+        if build_config.skip_if_error {
+            // hide errors, but emit a warning
+            let result = add_entries();
+            if result.is_err() {
+                let warning = format!(
+                    "An Error occurred during processing of {}. \
+                    VERGEN_{}_* may be incomplete.",
+                    "Build", "BUILD"
+                );
+                config.warnings_mut().push(warning);
+            }
+            Ok(())
+        } else {
+            add_entries()
+        }
+    } else {
+        Ok(())
     }
-    Ok(())
 }
 
 #[cfg(feature = "build")]