Auto merge of #55933 - euclio:doc-panic, r=QuietMisdreavus

emit error when doc generation fails

Fixes #41813.

The diagnostic looks something like this:

```
error: couldn't generate documentation: No space left on device (os error 28)
  |
  = note: failed to create or modify "/path/to/crate/target/doc/src/lazycell"
```

4 files changed, 43 insertions, 5 deletions

diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index 2c4ddf38e98..3365eb6d780 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -202,8 +202,8 @@ impl Impl {
 
 #[derive(Debug)]
 pub struct Error {
-    file: PathBuf,
-    error: io::Error,
+    pub file: PathBuf,
+    pub error: io::Error,
 }
 
 impl error::Error for Error {
diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
index 4b043b26d86..b21f005c06b 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -387,9 +387,21 @@ fn main_args(args: &[String]) -> isize {
         info!("going to format");
         let (error_format, treat_err_as_bug, ui_testing) = diag_opts;
         let diag = core::new_handler(error_format, None, treat_err_as_bug, ui_testing);
-        html::render::run(krate, renderopts, passes.into_iter().collect(), renderinfo, &diag)
-            .expect("failed to generate documentation");
-        0
+        match html::render::run(
+            krate,
+            renderopts,
+            passes.into_iter().collect(),
+            renderinfo,
+            &diag,
+        ) {
+            Ok(_) => rustc_driver::EXIT_SUCCESS,
+            Err(e) => {
+                diag.struct_err(&format!("couldn't generate documentation: {}", e.error))
+                    .note(&format!("failed to create or modify \"{}\"", e.file.display()))
+                    .emit();
+                rustc_driver::EXIT_FAILURE
+            }
+        }
     })
 }
 
diff --git a/src/test/run-make-fulldeps/rustdoc-io-error/Makefile b/src/test/run-make-fulldeps/rustdoc-io-error/Makefile
new file mode 100644
index 00000000000..2055c9cbf2d
--- /dev/null
+++ b/src/test/run-make-fulldeps/rustdoc-io-error/Makefile
@@ -0,0 +1,25 @@
+-include ../tools.mk
+
+# This test verifies that rustdoc doesn't ICE when it encounters an IO error
+# while generating files. Ideally this would be a rustdoc-ui test, so we could
+# verify the error message as well.
+
+OUTPUT_DIR := "$(TMPDIR)/rustdoc-io-error"
+
+# Ignore Windows: the test uses `chmod`.
+ifndef IS_WINDOWS
+
+# This test operates by creating a temporary directory and modifying its
+# permissions so that it is not writable. We have to take special care to set
+# the permissions back to normal so that it's able to be deleted later.
+all:
+	mkdir -p $(OUTPUT_DIR)
+	chmod u-w $(OUTPUT_DIR)
+	-$(shell $(RUSTDOC) -o $(OUTPUT_DIR) foo.rs)
+	chmod u+w $(OUTPUT_DIR)
+	exit $($(.SHELLSTATUS) -eq 1)
+
+else
+all:
+
+endif
diff --git a/src/test/run-make-fulldeps/rustdoc-io-error/foo.rs b/src/test/run-make-fulldeps/rustdoc-io-error/foo.rs
new file mode 100644
index 00000000000..4a835673a59
--- /dev/null
+++ b/src/test/run-make-fulldeps/rustdoc-io-error/foo.rs
@@ -0,0 +1 @@
+pub struct Foo;