From b9e28974fa6465940de17756a862c17830f78a6a Mon Sep 17 00:00:00 2001
From: tanzaku <tanzaku@users.noreply.github.com>
Date: Tue, 22 Nov 2022 02:11:34 +0900
Subject: [PATCH 1/9] Add `ignore_missing_submod` config option

---
 Configurations.md            |  8 ++++++++
 src/config/mod.rs            |  2 ++
 src/formatting.rs            |  1 +
 src/modules.rs               | 11 +++++++++++
 tests/config/issue-5609.toml |  1 +
 tests/source/issue-5609.rs   |  7 +++++++
 tests/target/issue-5609.rs   |  5 +++++
 7 files changed, 35 insertions(+)
 create mode 100644 tests/config/issue-5609.toml
 create mode 100644 tests/source/issue-5609.rs
 create mode 100644 tests/target/issue-5609.rs

diff --git a/Configurations.md b/Configurations.md
index 2d01fb3bb3b..6d726a2c3da 100644
--- a/Configurations.md
+++ b/Configurations.md
@@ -1306,6 +1306,14 @@ If you want to ignore every file under the directory where you put your rustfmt.
 ignore = ["/"]
 ```
 
+## `ignore_missing_submod`
+
+Ignore missing submodule error.
+
+- **Default value**: `false`
+- **Possible values**: `true`, `false`
+- **Stable**: Yes
+
 ## `imports_indent`
 
 Indent style of imports
diff --git a/src/config/mod.rs b/src/config/mod.rs
index 9484b2e5829..45cf387f9ac 100644
--- a/src/config/mod.rs
+++ b/src/config/mod.rs
@@ -179,6 +179,7 @@ create_config! {
          or they are left with trailing whitespaces";
     ignore: IgnoreList, IgnoreList::default(), false,
         "Skip formatting the specified files and directories";
+    ignore_missing_submod: bool, false, true, "Ignore missing submodule error";
 
     // Not user-facing
     verbose: Verbosity, Verbosity::Normal, false, "How much to information to emit to the user";
@@ -697,6 +698,7 @@ show_parse_errors = true
 error_on_line_overflow = false
 error_on_unformatted = false
 ignore = []
+ignore_missing_submod = false
 emit_mode = "Files"
 make_backup = false
 "#,
diff --git a/src/formatting.rs b/src/formatting.rs
index 60361505a3f..06993329e93 100644
--- a/src/formatting.rs
+++ b/src/formatting.rs
@@ -135,6 +135,7 @@ fn format_project<T: FormatHandler>(
         &context.parse_session,
         directory_ownership.unwrap_or(DirectoryOwnership::UnownedViaBlock),
         !input_is_stdin && !config.skip_children(),
+        config.ignore_missing_submod(),
     )
     .visit_crate(&krate)?
     .into_iter()
diff --git a/src/modules.rs b/src/modules.rs
index af9a154a6ae..b143aa1e308 100644
--- a/src/modules.rs
+++ b/src/modules.rs
@@ -62,6 +62,7 @@ pub(crate) struct ModResolver<'ast, 'sess> {
     directory: Directory,
     file_map: FileModMap<'ast>,
     recursive: bool,
+    ignore_missing_submod: bool,
 }
 
 /// Represents errors while trying to resolve modules.
@@ -105,6 +106,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
         parse_sess: &'sess ParseSess,
         directory_ownership: DirectoryOwnership,
         recursive: bool,
+        ignore_missing_submod: bool,
     ) -> Self {
         ModResolver {
             directory: Directory {
@@ -114,6 +116,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
             file_map: BTreeMap::new(),
             parse_sess,
             recursive,
+            ignore_missing_submod,
         }
     }
 
@@ -249,6 +252,14 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
             // mod foo;
             // Look for an extern file.
             self.find_external_module(item.ident, &item.attrs, sub_mod)
+                .or_else(|err| match err.kind {
+                    ModuleResolutionErrorKind::NotFound { file: _ }
+                        if self.ignore_missing_submod =>
+                    {
+                        Ok(None)
+                    }
+                    _ => Err(err),
+                })
         } else {
             // An internal module (`mod foo { /* ... */ }`);
             Ok(Some(SubModKind::Internal(item)))
diff --git a/tests/config/issue-5609.toml b/tests/config/issue-5609.toml
new file mode 100644
index 00000000000..450ad952083
--- /dev/null
+++ b/tests/config/issue-5609.toml
@@ -0,0 +1 @@
+ignore_missing_submod = true
diff --git a/tests/source/issue-5609.rs b/tests/source/issue-5609.rs
new file mode 100644
index 00000000000..7fffec461d5
--- /dev/null
+++ b/tests/source/issue-5609.rs
@@ -0,0 +1,7 @@
+// rustfmt-config: issue-5609.toml
+
+mod missing_submod;
+
+fn test() {
+
+}
diff --git a/tests/target/issue-5609.rs b/tests/target/issue-5609.rs
new file mode 100644
index 00000000000..0626c77fb75
--- /dev/null
+++ b/tests/target/issue-5609.rs
@@ -0,0 +1,5 @@
+// rustfmt-config: issue-5609.toml
+
+mod missing_submod;
+
+fn test() {}

From 34fd63018a154e153774688609cab98f4838ab4c Mon Sep 17 00:00:00 2001
From: tanzaku <tanzaku@users.noreply.github.com>
Date: Sat, 26 Nov 2022 02:29:47 +0900
Subject: [PATCH 2/9] Remove an unnecessary configuration file for testing

---
 tests/config/issue-5609.toml | 1 -
 tests/source/issue-5609.rs   | 2 +-
 tests/target/issue-5609.rs   | 2 +-
 3 files changed, 2 insertions(+), 3 deletions(-)
 delete mode 100644 tests/config/issue-5609.toml

diff --git a/tests/config/issue-5609.toml b/tests/config/issue-5609.toml
deleted file mode 100644
index 450ad952083..00000000000
--- a/tests/config/issue-5609.toml
+++ /dev/null
@@ -1 +0,0 @@
-ignore_missing_submod = true
diff --git a/tests/source/issue-5609.rs b/tests/source/issue-5609.rs
index 7fffec461d5..bb6170b2b45 100644
--- a/tests/source/issue-5609.rs
+++ b/tests/source/issue-5609.rs
@@ -1,4 +1,4 @@
-// rustfmt-config: issue-5609.toml
+// rustfmt-ignore_missing_submod: true
 
 mod missing_submod;
 
diff --git a/tests/target/issue-5609.rs b/tests/target/issue-5609.rs
index 0626c77fb75..c4ccdc4202e 100644
--- a/tests/target/issue-5609.rs
+++ b/tests/target/issue-5609.rs
@@ -1,4 +1,4 @@
-// rustfmt-config: issue-5609.toml
+// rustfmt-ignore_missing_submod: true
 
 mod missing_submod;
 

From b6d27d33672f098dfb5040da6453f8021f2a92f5 Mon Sep 17 00:00:00 2001
From: tanzaku <tanzaku@users.noreply.github.com>
Date: Sun, 27 Nov 2022 14:14:23 +0900
Subject: [PATCH 3/9] Add skip_children option explicitly

---
 tests/source/issue-5609.rs | 1 +
 tests/target/issue-5609.rs | 1 +
 2 files changed, 2 insertions(+)

diff --git a/tests/source/issue-5609.rs b/tests/source/issue-5609.rs
index bb6170b2b45..296464846b7 100644
--- a/tests/source/issue-5609.rs
+++ b/tests/source/issue-5609.rs
@@ -1,4 +1,5 @@
 // rustfmt-ignore_missing_submod: true
+// rustfmt-skip_children: false
 
 mod missing_submod;
 
diff --git a/tests/target/issue-5609.rs b/tests/target/issue-5609.rs
index c4ccdc4202e..c38cfc17604 100644
--- a/tests/target/issue-5609.rs
+++ b/tests/target/issue-5609.rs
@@ -1,4 +1,5 @@
 // rustfmt-ignore_missing_submod: true
+// rustfmt-skip_children: false
 
 mod missing_submod;
 

From 2faae327997aa16d000251b48b4c4fe352ad1203 Mon Sep 17 00:00:00 2001
From: tanzaku <tanzaku@users.noreply.github.com>
Date: Sun, 27 Nov 2022 14:19:13 +0900
Subject: [PATCH 4/9] Mark the ignore_missing_submod option as unstable

---
 Configurations.md | 2 +-
 src/config/mod.rs | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/Configurations.md b/Configurations.md
index 6d726a2c3da..84dec58faa1 100644
--- a/Configurations.md
+++ b/Configurations.md
@@ -1312,7 +1312,7 @@ Ignore missing submodule error.
 
 - **Default value**: `false`
 - **Possible values**: `true`, `false`
-- **Stable**: Yes
+- **Stable**: No
 
 ## `imports_indent`
 
diff --git a/src/config/mod.rs b/src/config/mod.rs
index 45cf387f9ac..6d2169599d1 100644
--- a/src/config/mod.rs
+++ b/src/config/mod.rs
@@ -179,7 +179,7 @@ create_config! {
          or they are left with trailing whitespaces";
     ignore: IgnoreList, IgnoreList::default(), false,
         "Skip formatting the specified files and directories";
-    ignore_missing_submod: bool, false, true, "Ignore missing submodule error";
+    ignore_missing_submod: bool, false, false, "Ignore missing submodule error";
 
     // Not user-facing
     verbose: Verbosity, Verbosity::Normal, false, "How much to information to emit to the user";

From aa4cd2639d60be95b76ad5892da59b2e7e7b08fb Mon Sep 17 00:00:00 2001
From: tanzaku <tanzaku@users.noreply.github.com>
Date: Sun, 27 Nov 2022 16:56:10 +0900
Subject: [PATCH 5/9] Add tests

---
 tests/rustfmt/main.rs | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/tests/rustfmt/main.rs b/tests/rustfmt/main.rs
index 87b55ca1d1d..801a7490284 100644
--- a/tests/rustfmt/main.rs
+++ b/tests/rustfmt/main.rs
@@ -1,8 +1,8 @@
 //! Integration tests for rustfmt.
 
 use std::env;
-use std::fs::remove_file;
-use std::path::Path;
+use std::fs::{read_to_string, remove_file};
+use std::path::{Path, PathBuf};
 use std::process::Command;
 
 use rustfmt_config_proc_macro::rustfmt_only_ci_test;
@@ -200,3 +200,30 @@ fn rustfmt_emits_error_when_control_brace_style_is_always_next_line() {
     let (_stdout, stderr) = rustfmt(&args);
     assert!(!stderr.contains("error[internal]: left behind trailing whitespace"))
 }
+
+#[test]
+fn ignore_missing_sub_mod_false() {
+    // Ensure that missing submodules cause module not found errors when trying to
+    // resolve submodules with `skip_children=false` and `ignore_missing_submod=false`
+    let args = [
+        "--config=skip_children=false,ignore_missing_submod=false",
+        "tests/source/issue-5609.rs",
+    ];
+    let (_stdout, stderr) = rustfmt(&args);
+    // Module resolution fails because we're unable to find `missing_submod.rs`
+    assert!(stderr.contains("missing_submod.rs does not exist"))
+}
+
+#[test]
+fn ignore_missing_sub_mod_true() {
+    // Ensure that missing submodules don't cause module not found errors when trying to
+    // resolve submodules with `skip_children=false` and `ignore_missing_submod=true`.
+    let args = [
+        "--emit=stdout",
+        "--config=skip_children=false,ignore_missing_submod=true",
+        "tests/source/issue-5609.rs",
+    ];
+    let (stdout, _stderr) = rustfmt(&args);
+    let target = read_to_string(PathBuf::from("tests/target/issue-5609.rs")).unwrap();
+    assert!(stdout.ends_with(&target));
+}

From 50e7197e7851f9b42310ff2ad52a07d74348cc07 Mon Sep 17 00:00:00 2001
From: tanzaku <tanzaku@users.noreply.github.com>
Date: Sun, 27 Nov 2022 21:36:16 +0900
Subject: [PATCH 6/9] Update ignore_missing_submod option description

---
 Configurations.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Configurations.md b/Configurations.md
index 84dec58faa1..d187ed18d52 100644
--- a/Configurations.md
+++ b/Configurations.md
@@ -1309,6 +1309,7 @@ ignore = ["/"]
 ## `ignore_missing_submod`
 
 Ignore missing submodule error.
+By default, missing modules will lead to module not found errors and rustfmt won't format anything.
 
 - **Default value**: `false`
 - **Possible values**: `true`, `false`

From 4bb045340276b8fade94dd822dbb34ba40c4ed49 Mon Sep 17 00:00:00 2001
From: tanzaku <tanzaku@users.noreply.github.com>
Date: Thu, 1 Feb 2024 19:58:04 +0900
Subject: [PATCH 7/9] Update Configuration.md

---
 Configurations.md | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/Configurations.md b/Configurations.md
index d187ed18d52..70abb009e9e 100644
--- a/Configurations.md
+++ b/Configurations.md
@@ -1306,15 +1306,26 @@ If you want to ignore every file under the directory where you put your rustfmt.
 ignore = ["/"]
 ```
 
-## `ignore_missing_submod`
+## `report_missing_submod`
 
-Ignore missing submodule error.
-By default, missing modules will lead to module not found errors and rustfmt won't format anything.
+Controls whether to report missing submodules and whether rustfmt will format.
 
-- **Default value**: `false`
-- **Possible values**: `true`, `false`
+- **Default value**: `Error`
+- **Possible values**: `Error`, `Warn`, `Ignore`
 - **Stable**: No
 
+#### `Error` (default):
+
+Missing modules will lead to module not found errors and rustfmt won't format anything.
+
+#### `Warn`
+
+Missing modules will lead to module not found warnings and rustfmt will format.
+
+#### `Ignore`
+
+Ignores missing submodule error and rustfmt will format.
+
 ## `imports_indent`
 
 Indent style of imports

From f678369ce39f5d2591bc94a8ef1e81bf45053269 Mon Sep 17 00:00:00 2001
From: tanzaku <tanzaku@users.noreply.github.com>
Date: Thu, 1 Feb 2024 20:22:20 +0900
Subject: [PATCH 8/9] Changes error reporting to an Error, Warn, and Ignore
 model

---
 src/config/mod.rs     |  5 +++--
 src/config/options.rs | 11 +++++++++++
 src/formatting.rs     |  2 +-
 src/modules.rs        | 16 +++++++++++-----
 4 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/src/config/mod.rs b/src/config/mod.rs
index 6d2169599d1..772b09dd8c4 100644
--- a/src/config/mod.rs
+++ b/src/config/mod.rs
@@ -179,7 +179,8 @@ create_config! {
          or they are left with trailing whitespaces";
     ignore: IgnoreList, IgnoreList::default(), false,
         "Skip formatting the specified files and directories";
-    ignore_missing_submod: bool, false, false, "Ignore missing submodule error";
+    report_missing_submod: ReportMissingSubmod, ReportMissingSubmod::Error, false,
+        "Report missing submodule";
 
     // Not user-facing
     verbose: Verbosity, Verbosity::Normal, false, "How much to information to emit to the user";
@@ -698,7 +699,7 @@ show_parse_errors = true
 error_on_line_overflow = false
 error_on_unformatted = false
 ignore = []
-ignore_missing_submod = false
+report_missing_submod = "Error"
 emit_mode = "Files"
 make_backup = false
 "#,
diff --git a/src/config/options.rs b/src/config/options.rs
index 3c5c713a33a..e9edc607f0b 100644
--- a/src/config/options.rs
+++ b/src/config/options.rs
@@ -494,3 +494,14 @@ pub enum StyleEdition {
     /// [Edition 2024]().
     Edition2024,
 }
+
+/// Controls whether to report missing submodules and whether rustfmt will format.
+#[config_type]
+pub enum ReportMissingSubmod {
+    /// Missing modules will lead to module not found errors and rustfmt won't format anything.
+    Error,
+    /// Missing modules will lead to module not found warnings and rustfmt will format.
+    Warn,
+    /// Ignores missing submodule error and rustfmt will format.
+    Ignore,
+}
diff --git a/src/formatting.rs b/src/formatting.rs
index 06993329e93..f24233c91d7 100644
--- a/src/formatting.rs
+++ b/src/formatting.rs
@@ -135,7 +135,7 @@ fn format_project<T: FormatHandler>(
         &context.parse_session,
         directory_ownership.unwrap_or(DirectoryOwnership::UnownedViaBlock),
         !input_is_stdin && !config.skip_children(),
-        config.ignore_missing_submod(),
+        config.report_missing_submod(),
     )
     .visit_crate(&krate)?
     .into_iter()
diff --git a/src/modules.rs b/src/modules.rs
index b143aa1e308..38f993fbcfa 100644
--- a/src/modules.rs
+++ b/src/modules.rs
@@ -10,7 +10,7 @@ use thin_vec::ThinVec;
 use thiserror::Error;
 
 use crate::attr::MetaVisitor;
-use crate::config::FileName;
+use crate::config::{FileName, ReportMissingSubmod};
 use crate::items::is_mod_decl;
 use crate::parse::parser::{
     Directory, DirectoryOwnership, ModError, ModulePathSuccess, Parser, ParserError,
@@ -62,7 +62,7 @@ pub(crate) struct ModResolver<'ast, 'sess> {
     directory: Directory,
     file_map: FileModMap<'ast>,
     recursive: bool,
-    ignore_missing_submod: bool,
+    report_missing_submod: ReportMissingSubmod,
 }
 
 /// Represents errors while trying to resolve modules.
@@ -106,7 +106,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
         parse_sess: &'sess ParseSess,
         directory_ownership: DirectoryOwnership,
         recursive: bool,
-        ignore_missing_submod: bool,
+        report_missing_submod: ReportMissingSubmod,
     ) -> Self {
         ModResolver {
             directory: Directory {
@@ -116,7 +116,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
             file_map: BTreeMap::new(),
             parse_sess,
             recursive,
-            ignore_missing_submod,
+            report_missing_submod,
         }
     }
 
@@ -254,10 +254,16 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
             self.find_external_module(item.ident, &item.attrs, sub_mod)
                 .or_else(|err| match err.kind {
                     ModuleResolutionErrorKind::NotFound { file: _ }
-                        if self.ignore_missing_submod =>
+                        if self.report_missing_submod == ReportMissingSubmod::Ignore =>
                     {
                         Ok(None)
                     }
+                    ModuleResolutionErrorKind::NotFound { file: _ }
+                        if self.report_missing_submod == ReportMissingSubmod::Warn =>
+                    {
+                        eprintln!("Warning: {}", err);
+                        Ok(None)
+                    }
                     _ => Err(err),
                 })
         } else {

From fcc06f96af07f6423d052191667dc64da2690a25 Mon Sep 17 00:00:00 2001
From: tanzaku <tanzaku@users.noreply.github.com>
Date: Thu, 1 Feb 2024 22:12:50 +0900
Subject: [PATCH 9/9] Fix tests

---
 tests/rustfmt/main.rs        | 27 ++++++++++++++++++++++-----
 tests/source/issue-5609-2.rs |  8 ++++++++
 tests/source/issue-5609.rs   |  2 +-
 tests/target/issue-5609-2.rs |  6 ++++++
 tests/target/issue-5609.rs   |  2 +-
 5 files changed, 38 insertions(+), 7 deletions(-)
 create mode 100644 tests/source/issue-5609-2.rs
 create mode 100644 tests/target/issue-5609-2.rs

diff --git a/tests/rustfmt/main.rs b/tests/rustfmt/main.rs
index 801a7490284..74eae3e9c08 100644
--- a/tests/rustfmt/main.rs
+++ b/tests/rustfmt/main.rs
@@ -202,11 +202,11 @@ fn rustfmt_emits_error_when_control_brace_style_is_always_next_line() {
 }
 
 #[test]
-fn ignore_missing_sub_mod_false() {
+fn report_missing_sub_mod_error() {
     // Ensure that missing submodules cause module not found errors when trying to
-    // resolve submodules with `skip_children=false` and `ignore_missing_submod=false`
+    // resolve submodules with `skip_children=false` and `report_missing_submod=Error`
     let args = [
-        "--config=skip_children=false,ignore_missing_submod=false",
+        "--config=skip_children=false,report_missing_submod=Error",
         "tests/source/issue-5609.rs",
     ];
     let (_stdout, stderr) = rustfmt(&args);
@@ -214,13 +214,30 @@ fn ignore_missing_sub_mod_false() {
     assert!(stderr.contains("missing_submod.rs does not exist"))
 }
 
+#[test]
+fn report_missing_sub_mod_warn() {
+    // Ensure that missing submodules cause module not found warnings when trying to
+    // resolve submodules with `skip_children=false` and `report_missing_submod=Warn`
+    let args = [
+        "--emit=stdout",
+        "--config=skip_children=false,report_missing_submod=Warn",
+        "tests/source/issue-5609.rs",
+    ];
+    let (stdout, stderr) = rustfmt(&args);
+    // Module resolution succeed but we emit warnings because we're unable to find `missing_submod.rs`
+    assert!(stderr.contains("missing_submod.rs does not exist"));
+
+    let target = read_to_string(PathBuf::from("tests/target/issue-5609.rs")).unwrap();
+    assert!(stdout.ends_with(&target));
+}
+
 #[test]
 fn ignore_missing_sub_mod_true() {
     // Ensure that missing submodules don't cause module not found errors when trying to
-    // resolve submodules with `skip_children=false` and `ignore_missing_submod=true`.
+    // resolve submodules with `skip_children=false` and `report_missing_submod=Ignore`.
     let args = [
         "--emit=stdout",
-        "--config=skip_children=false,ignore_missing_submod=true",
+        "--config=skip_children=false,report_missing_submod=Ignore",
         "tests/source/issue-5609.rs",
     ];
     let (stdout, _stderr) = rustfmt(&args);
diff --git a/tests/source/issue-5609-2.rs b/tests/source/issue-5609-2.rs
new file mode 100644
index 00000000000..413c0829f4d
--- /dev/null
+++ b/tests/source/issue-5609-2.rs
@@ -0,0 +1,8 @@
+// rustfmt-report_missing_submod: Warn
+// rustfmt-skip_children: false
+
+mod missing_submod;
+
+fn test() {
+
+}
diff --git a/tests/source/issue-5609.rs b/tests/source/issue-5609.rs
index 296464846b7..d7112a4d262 100644
--- a/tests/source/issue-5609.rs
+++ b/tests/source/issue-5609.rs
@@ -1,4 +1,4 @@
-// rustfmt-ignore_missing_submod: true
+// rustfmt-report_missing_submod: Ignore
 // rustfmt-skip_children: false
 
 mod missing_submod;
diff --git a/tests/target/issue-5609-2.rs b/tests/target/issue-5609-2.rs
new file mode 100644
index 00000000000..f7b454216bf
--- /dev/null
+++ b/tests/target/issue-5609-2.rs
@@ -0,0 +1,6 @@
+// rustfmt-report_missing_submod: Warn
+// rustfmt-skip_children: false
+
+mod missing_submod;
+
+fn test() {}
diff --git a/tests/target/issue-5609.rs b/tests/target/issue-5609.rs
index c38cfc17604..184cc0aed60 100644
--- a/tests/target/issue-5609.rs
+++ b/tests/target/issue-5609.rs
@@ -1,4 +1,4 @@
-// rustfmt-ignore_missing_submod: true
+// rustfmt-report_missing_submod: Ignore
 // rustfmt-skip_children: false
 
 mod missing_submod;