add test for 3984

This is fixed by backporting 3999

tests/source/issue-3984/imports_granularity_crate.rs

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+// rustfmt-imports_granularity: Crate
+
+// See https://github.com/rust-lang/rustfmt/issues/3984
+use a::{item /* comment */};
+use b::{
+    a,
+    // comment
+    item,
+};
+use c::item /* comment */;
+use d::item; // really long comment (with `use` exactly 100 characters) ____________________________
+
+use std::e::{/* it's a comment! */ bar /* and another */};
+use std::f::{/* it's a comment! */ bar};
+use std::g::{bar /* and another */};

tests/source/issue-3984/imports_granularity_item.rs

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+// rustfmt-imports_granularity: Item
+
+// See https://github.com/rust-lang/rustfmt/issues/3984
+use a::{item /* comment */};
+use b::{
+    a,
+    // comment
+    item,
+};
+use c::item /* comment */;
+use d::item; // really long comment (with `use` exactly 100 characters) ____________________________
+
+use std::e::{/* it's a comment! */ bar /* and another */};
+use std::f::{/* it's a comment! */ bar};
+use std::g::{bar /* and another */};

tests/source/issue-3984/imports_granularity_module.rs

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+// rustfmt-imports_granularity: Module
+
+// See https://github.com/rust-lang/rustfmt/issues/3984
+use a::{item /* comment */};
+use b::{
+    a,
+    // comment
+    item,
+};
+use c::item /* comment */;
+use d::item; // really long comment (with `use` exactly 100 characters) ____________________________
+
+use std::e::{/* it's a comment! */ bar /* and another */};
+use std::f::{/* it's a comment! */ bar};
+use std::g::{bar /* and another */};

tests/source/issue-3984/imports_granularity_one.rs

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+// rustfmt-imports_granularity: One
+
+// See https://github.com/rust-lang/rustfmt/issues/3984
+use a::{item /* comment */};
+use b::{
+    a,
+    // comment
+    item,
+};
+use c::item /* comment */;
+use d::item; // really long comment (with `use` exactly 100 characters) ____________________________
+
+use std::e::{/* it's a comment! */ bar /* and another */};
+use std::f::{/* it's a comment! */ bar};
+use std::g::{bar /* and another */};

tests/source/issue-3984/imports_granularity_preserve.rs

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+// rustfmt-imports_granularity: Preserve
+
+// See https://github.com/rust-lang/rustfmt/issues/3984
+use a::{item /* comment */};
+use b::{
+    a,
+    // comment
+    item,
+};
+use c::item /* comment */;
+use d::item; // really long comment (with `use` exactly 100 characters) ____________________________
+
+use std::e::{/* it's a comment! */ bar /* and another */};
+use std::f::{/* it's a comment! */ bar};
+use std::g::{bar /* and another */};

tests/target/issue-3984/imports_granularity_crate.rs

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+// rustfmt-imports_granularity: Crate
+
+// See https://github.com/rust-lang/rustfmt/issues/3984
+use a::{item /* comment */};
+use b::{
+    a,
+    // comment
+    item,
+};
+use c::item; /* comment */
+use d::item; // really long comment (with `use` exactly 100 characters) ____________________________
+
+use std::e::{/* it's a comment! */ bar /* and another */};
+use std::f::{/* it's a comment! */ bar};
+use std::g::{bar /* and another */};

tests/target/issue-3984/imports_granularity_item.rs

@@ -0,0 +1,15 @@
+// rustfmt-imports_granularity: Item
+
+// See https://github.com/rust-lang/rustfmt/issues/3984
+use a::{item /* comment */};
+use b::{
+    a,
+    // comment
+    item,
+};
+use c::item; /* comment */
+use d::item; // really long comment (with `use` exactly 100 characters) ____________________________
+
+use std::e::{/* it's a comment! */ bar /* and another */};
+use std::f::{/* it's a comment! */ bar};
+use std::g::{bar /* and another */};

tests/target/issue-3984/imports_granularity_module.rs

@@ -0,0 +1,15 @@
+// rustfmt-imports_granularity: Module
+
+// See https://github.com/rust-lang/rustfmt/issues/3984
+use a::{item /* comment */};
+use b::{
+    a,
+    // comment
+    item,
+};
+use c::item; /* comment */
+use d::item; // really long comment (with `use` exactly 100 characters) ____________________________
+
+use std::e::{/* it's a comment! */ bar /* and another */};
+use std::f::{/* it's a comment! */ bar};
+use std::g::{bar /* and another */};

tests/target/issue-3984/imports_granularity_one.rs

@@ -0,0 +1,15 @@
+// rustfmt-imports_granularity: One
+
+// See https://github.com/rust-lang/rustfmt/issues/3984
+use a::{item /* comment */};
+use b::{
+    a,
+    // comment
+    item,
+};
+use c::item; /* comment */
+use d::item; // really long comment (with `use` exactly 100 characters) ____________________________
+
+use std::e::{/* it's a comment! */ bar /* and another */};
+use std::f::{/* it's a comment! */ bar};
+use std::g::{bar /* and another */};

tests/target/issue-3984/imports_granularity_preserve.rs

@@ -0,0 +1,15 @@
+// rustfmt-imports_granularity: Preserve
+
+// See https://github.com/rust-lang/rustfmt/issues/3984
+use a::{item /* comment */};
+use b::{
+    a,
+    // comment
+    item,
+};
+use c::item; /* comment */
+use d::item; // really long comment (with `use` exactly 100 characters) ____________________________
+
+use std::e::{/* it's a comment! */ bar /* and another */};
+use std::f::{/* it's a comment! */ bar};
+use std::g::{bar /* and another */};