tamer: pipeline: Allow reporting on entire Result

The report acts as the sink for `load_xmlo` and `parse_package_xml`.  At the
moment, the type is `()`, and so there's nothing to report on but the
error.  But the idea is to add logging via `AirAggregate::Object`, which is
currently just `()`.

This change therefore is only a refactoring---it changes no functionality
but sets up for future changes.

This also introduces consistency with `lower_xmli` in use of `terminal` for
the final operation.

DEV-13162

tamer/src/bin/tamec.rs

@@ -119,13 +119,15 @@ fn compile<R: Reporter>(
 
     let mut ebuf = String::new();
 
-    let report_err = |e: RecoverableError| {
-        // See below note about buffering.
-        ebuf.clear();
-        writeln!(ebuf, "{}", reporter.render(&e))?;
-        println!("{ebuf}");
+    let report_err = |result: Result<(), RecoverableError>| {
+        result.or_else(|e| {
+            // See below note about buffering.
+            ebuf.clear();
+            writeln!(ebuf, "{}", reporter.render(&e))?;
+            println!("{ebuf}");
 
-        Ok::<_, UnrecoverableError>(())
+            Ok::<_, UnrecoverableError>(())
+        })
     };
 
     // TODO: We're just echoing back out XIR,

tamer/src/ld/poc.rs

@@ -49,6 +49,7 @@ use crate::{
 };
 use fxhash::FxBuildHasher;
 use std::{
+    convert::identity,
     error::Error,
     fmt::{self, Display},
     fs,
@@ -106,7 +107,7 @@ fn load_xmlo<P: AsRef<Path>, S: Escaper>(
     let src = &mut lowerable(XmlXirReader::new(file, escaper, ctx));
 
     let (mut air_ctx, mut state) =
-        pipeline::load_xmlo::<TameldError, _>(src, air_ctx, state, Err)?;
+        pipeline::load_xmlo::<TameldError, _>(src, air_ctx, state, identity)?;
 
     let mut dir = path;
     dir.pop();

tamer/src/pipeline.rs

@@ -77,7 +77,7 @@ pub fn load_xmlo<ER: Diagnostic, EU: Diagnostic>(
     src: impl LowerSource<UnknownToken, XirToken, XirError>,
     air_ctx: AirAggregateCtx,
     xmlo_ctx: XmloAirContext,
-    mut report_err: impl FnMut(ER) -> Result<(), EU>,
+    report: impl FnMut(Result<(), ER>) -> Result<(), EU>,
 ) -> Result<(AirAggregateCtx, XmloAirContext), EU>
 where
     ER: From<ParseError<UnknownToken, XirError>>
@@ -107,13 +107,7 @@ where
 
             Lower::<XmloReader, XmloToAir, _>::lower_with_context(&mut iter, xmlo_ctx, |air| {
                 Lower::<XmloToAir, AirAggregate, _>::lower_with_context(air, air_ctx, |end| {
-                    end.fold(Ok(()), |x, result| match result {
-                        Ok(_) => x,
-                        Err(e) => {
-                            report_err(e)?;
-                            x
-                        }
-                    })
+                    terminal::<AirAggregate, _>(end).try_for_each(report)
                 })
             })
         })
@@ -129,7 +123,7 @@ where
 pub fn parse_package_xml<ER: Diagnostic, EU: Diagnostic>(
     src: impl LowerSource<UnknownToken, XirToken, XirError>,
     air_ctx: AirAggregateCtx,
-    mut report_err: impl FnMut(ER) -> Result<(), EU>,
+    report: impl FnMut(Result<(), ER>) -> Result<(), EU>,
 ) -> Result<AirAggregateCtx, EU>
 where
     ER: From<ParseError<UnknownToken, XirError>>
@@ -152,13 +146,7 @@ where
                 Lower::<TplShortDesugar, InterpolateNir, _>::lower(nir, |nir| {
                     Lower::<InterpolateNir, NirToAir, _>::lower(nir, |air| {
                         Lower::<NirToAir, AirAggregate, _>::lower_with_context(air, air_ctx, |end| {
-                            end.fold(Ok(()), |x, result| match result {
-                                Ok(_) => x,
-                                Err(e) => {
-                                    report_err(e)?;
-                                    x
-                                }
-                            })
+                            terminal::<AirAggregate, _>(end).try_for_each(report)
                         })
                     })
                 })