feat(source-code): Don't override provided source code (#300)

BREAKING CHANGE: Source code is no longer overridden if it was provided by the diagnostic's own `source_code()` impl.

src/eyreish/wrapper.rs

@@ -163,7 +163,7 @@ impl<E: Diagnostic, C: SourceCode> Diagnostic for WithSourceCode<E, C> {
     }
 
     fn source_code(&self) -> Option<&dyn miette::SourceCode> {
-        Some(&self.source_code)
+        self.error.source_code().or(Some(&self.source_code))
     }
 
     fn related<'a>(&'a self) -> Option<Box<dyn Iterator<Item = &'a dyn Diagnostic> + 'a>> {
@@ -197,7 +197,7 @@ impl<C: SourceCode> Diagnostic for WithSourceCode<Report, C> {
     }
 
     fn source_code(&self) -> Option<&dyn miette::SourceCode> {
-        Some(&self.source_code)
+        self.error.source_code().or(Some(&self.source_code))
     }
 
     fn related<'a>(&'a self) -> Option<Box<dyn Iterator<Item = &'a dyn Diagnostic> + 'a>> {
@@ -232,3 +232,88 @@ impl<C> StdError for WithSourceCode<Report, C> {
         self.error.source()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use thiserror::Error;
+
+    use crate::{Diagnostic, LabeledSpan, Report, SourceCode, SourceSpan};
+
+    #[derive(Error, Debug)]
+    #[error("inner")]
+    struct Inner {
+        pub(crate) at: SourceSpan,
+        pub(crate) source_code: Option<String>,
+    }
+
+    impl Diagnostic for Inner {
+        fn labels(&self) -> Option<Box<dyn Iterator<Item = LabeledSpan> + '_>> {
+            Some(Box::new(std::iter::once(LabeledSpan::underline(self.at))))
+        }
+
+        fn source_code(&self) -> Option<&dyn SourceCode> {
+            self.source_code.as_ref().map(|s| s as _)
+        }
+    }
+
+    #[derive(Error, Debug)]
+    #[error("outer")]
+    struct Outer {
+        pub(crate) errors: Vec<Inner>,
+    }
+
+    impl Diagnostic for Outer {
+        fn related<'a>(&'a self) -> Option<Box<dyn Iterator<Item = &'a dyn Diagnostic> + 'a>> {
+            Some(Box::new(self.errors.iter().map(|e| e as _)))
+        }
+    }
+
+    #[test]
+    fn no_override() {
+        let inner_source = "hello world";
+        let outer_source = "abc";
+
+        let report = Report::from(Inner {
+            at: (0..5).into(),
+            source_code: Some(inner_source.to_string()),
+        })
+        .with_source_code(outer_source.to_string());
+
+        let underlined = String::from_utf8(
+            report
+                .source_code()
+                .unwrap()
+                .read_span(&(0..5).into(), 0, 0)
+                .unwrap()
+                .data()
+                .to_vec(),
+        )
+        .unwrap();
+        assert_eq!(underlined, "hello");
+    }
+
+    #[test]
+    #[cfg(feature = "fancy")]
+    fn two_source_codes() {
+        let inner_source = "hello world";
+        let outer_source = "abc";
+
+        let report = Report::from(Outer {
+            errors: vec![
+                Inner {
+                    at: (0..5).into(),
+                    source_code: Some(inner_source.to_string()),
+                },
+                Inner {
+                    at: (1..2).into(),
+                    source_code: None,
+                },
+            ],
+        })
+        .with_source_code(outer_source.to_string());
+
+        let message = format!("{:?}", report);
+        assert!(message.contains(inner_source));
+        assert!(message.contains(outer_source));
+    }
+}