Factor out handle_render_command_error

This moves `handle_render_command_error` out to the crate root so that
it can later be shared with `CmdPreprocessor`.

Author: ehuss

crates/mdbook-driver/src/builtin_renderers/mod.rs

@@ -6,7 +6,6 @@ use anyhow::{Context, Result, bail};
 use log::{error, info, trace, warn};
 use mdbook_renderer::{RenderContext, Renderer};
 use std::fs;
-use std::io::{self, ErrorKind};
 use std::process::Stdio;
 
 pub use self::markdown_renderer::MarkdownRenderer;
@@ -49,41 +48,6 @@ impl CmdRenderer {
     }
 }
 
-impl CmdRenderer {
-    fn handle_render_command_error(&self, ctx: &RenderContext, error: io::Error) -> Result<()> {
-        if let ErrorKind::NotFound = error.kind() {
-            // Look for "output.{self.name}.optional".
-            // If it exists and is true, treat this as a warning.
-            // Otherwise, fail the build.
-
-            let optional_key = format!("output.{}.optional", self.name);
-
-            let is_optional = match ctx.config.get(&optional_key) {
-                Ok(Some(value)) => value,
-                Err(e) => bail!("expected bool for `{optional_key}`: {e}"),
-                Ok(None) => false,
-            };
-
-            if is_optional {
-                warn!(
-                    "The command `{}` for backend `{}` was not found, \
-                    but was marked as optional.",
-                    self.cmd, self.name
-                );
-                return Ok(());
-            } else {
-                error!(
-                    "The command `{0}` wasn't found, is the \"{1}\" backend installed? \
-                    If you want to ignore this error when the \"{1}\" backend is not installed, \
-                    set `optional = true` in the `[output.{1}]` section of the book.toml configuration file.",
-                    self.cmd, self.name
-                );
-            }
-        }
-        Err(error).with_context(|| "Unable to start the backend")?
-    }
-}
-
 impl Renderer for CmdRenderer {
     fn name(&self) -> &str {
         &self.name
@@ -92,6 +56,13 @@ impl Renderer for CmdRenderer {
     fn render(&self, ctx: &RenderContext) -> Result<()> {
         info!("Invoking the \"{}\" renderer", self.name);
 
+        let optional_key = format!("output.{}.optional", self.name);
+        let optional = match ctx.config.get(&optional_key) {
+            Ok(Some(value)) => value,
+            Err(e) => bail!("expected bool for `{optional_key}`: {e}"),
+            Ok(None) => false,
+        };
+
         let _ = fs::create_dir_all(&ctx.destination);
 
         let mut cmd = crate::compose_command(&self.cmd, &ctx.root)?;
@@ -103,7 +74,11 @@ impl Renderer for CmdRenderer {
             .spawn()
         {
             Ok(c) => c,
-            Err(e) => return self.handle_render_command_error(ctx, e),
+            Err(e) => {
+                return crate::handle_command_error(
+                    e, optional, "output", "backend", &self.name, &self.cmd,
+                );
+            }
         };
 
         let mut stdin = child.stdin.take().expect("Child has stdin");

crates/mdbook-driver/src/lib.rs

@@ -64,7 +64,8 @@ pub mod init;
 mod load;
 mod mdbook;
 
-use anyhow::{Result, bail};
+use anyhow::{Context, Result, bail};
+use log::{error, warn};
 pub use mdbook::MDBook;
 pub use mdbook_core::{book, config, errors};
 use shlex::Shlex;
@@ -95,3 +96,30 @@ fn compose_command(cmd: &str, root: &Path) -> Result<Command> {
 
     Ok(cmd)
 }
+
+/// Handles a failure for a preprocessor or renderer.
+fn handle_command_error(
+    error: std::io::Error,
+    optional: bool,
+    key: &str,
+    what: &str,
+    name: &str,
+    cmd: &str,
+) -> Result<()> {
+    if let std::io::ErrorKind::NotFound = error.kind() {
+        if optional {
+            warn!(
+                "The command `{cmd}` for {what} `{name}` was not found, \
+                 but is marked as optional.",
+            );
+            return Ok(());
+        } else {
+            error!(
+                "The command `{cmd}` wasn't found, is the `{name}` {what} installed? \
+                If you want to ignore this error when the `{name}` {what} is not installed, \
+                set `optional = true` in the `[{key}.{name}]` section of the book.toml configuration file.",
+            );
+        }
+    }
+    Err(error).with_context(|| format!("Unable to run the {what} `{name}`"))?
+}

tests/testsuite/renderer.rs

@@ -85,9 +85,9 @@ fn missing_renderer() {
 [TIMESTAMP] [INFO] (mdbook_driver::mdbook): Book building has started
 [TIMESTAMP] [INFO] (mdbook_driver::mdbook): Running the missing backend
 [TIMESTAMP] [INFO] (mdbook_driver::builtin_renderers): Invoking the "missing" renderer
-[TIMESTAMP] [ERROR] (mdbook_driver::builtin_renderers): The command `trduyvbhijnorgevfuhn` wasn't found, is the "missing" backend installed? If you want to ignore this error when the "missing" backend is not installed, set `optional = true` in the `[output.missing]` section of the book.toml configuration file.
+[TIMESTAMP] [ERROR] (mdbook_driver): The command `trduyvbhijnorgevfuhn` wasn't found, is the `missing` backend installed? If you want to ignore this error when the `missing` backend is not installed, set `optional = true` in the `[output.missing]` section of the book.toml configuration file.
 [TIMESTAMP] [ERROR] (mdbook_core::utils): Error: Rendering failed
-[TIMESTAMP] [ERROR] (mdbook_core::utils): [TAB]Caused By: Unable to start the backend
+[TIMESTAMP] [ERROR] (mdbook_core::utils): [TAB]Caused By: Unable to run the backend `missing`
 [TIMESTAMP] [ERROR] (mdbook_core::utils): [TAB]Caused By: [NOT_FOUND]
 
 "#]]);
@@ -102,7 +102,7 @@ fn missing_optional_not_fatal() {
 [TIMESTAMP] [INFO] (mdbook_driver::mdbook): Book building has started
 [TIMESTAMP] [INFO] (mdbook_driver::mdbook): Running the missing backend
 [TIMESTAMP] [INFO] (mdbook_driver::builtin_renderers): Invoking the "missing" renderer
-[TIMESTAMP] [WARN] (mdbook_driver::builtin_renderers): The command `trduyvbhijnorgevfuhn` for backend `missing` was not found, but was marked as optional.
+[TIMESTAMP] [WARN] (mdbook_driver): The command `trduyvbhijnorgevfuhn` for backend `missing` was not found, but is marked as optional.
 
 "#]]);
     });