One-liner version of error message

Author: kornelski

src/lib.rs

@@ -427,6 +427,49 @@ impl fmt::Display for Error {
     }
 }
 
+impl Error {
+    /// Returns a concise version of the error message
+    pub fn error_message(&self) -> String {
+
+        // Extracts just the command name from WrappedCommand's output.
+        // The command name alone is not available in the Error enum.
+        fn trimmed_command(command: &str) -> &str {
+            let env_prefix = command.split_inclusive(' ')
+                .take_while(|arg| arg.starts_with("PKG_CONFIG") && arg.contains('='))
+                .map(|arg| arg.len())
+                .sum::<usize>();
+            command[env_prefix..].split(" --").next().unwrap()
+        }
+
+        match self {
+            Error::Command { command, cause } => match cause.kind() {
+                io::ErrorKind::NotFound => {
+                    format!("`{}` command not found. Is pkg-config installed?", trimmed_command(command))
+                }
+                _ => format!("Could not run `{}` command, because {}", trimmed_command(command), cause),
+            },
+            Error::Failure { command, output } => {
+                format!("Command `{}` failed with {}", trimmed_command(command), output.status)
+            }
+            Error::ProbeFailure {
+                name,
+                command,
+                output,
+            } => format!(
+                "The system library `{}` was not found, because command `{}` failed with {}",
+                name, trimmed_command(command), output.status
+            ),
+            Error::EnvNoPkgConfig(var) => {
+                format!("pkg-config has been disabled via {} env var", var)
+            }
+            Error::CrossCompilation => {
+                format!("pkg-config has not been set up to support cross-compilation")
+            }
+            _ => self.to_string(),
+        }
+    }
+}
+
 fn format_output(output: &Output, f: &mut fmt::Formatter<'_>) -> fmt::Result {
     let stdout = String::from_utf8_lossy(&output.stdout);
     if !stdout.is_empty() {