Scaffold uitest

Cargo.lock

@@ -232,6 +232,12 @@ version = "1.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
 
+[[package]]
+name = "bitflags"
+version = "2.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "487f1e0fcbe47deb8b0574e646def1c903389d95241dd1bbcc6ce4a715dfc0c1"
+
 [[package]]
 name = "bitmaps"
 version = "2.1.0"
@@ -420,7 +426,7 @@ version = "2.34.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a0610544180c38b88101fecf2dd634b174a62eef6946f84dfc6a7127512b381c"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "textwrap 0.11.0",
  "unicode-width",
 ]
@@ -432,14 +438,42 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "71655c45cb9845d3270c9d6df84ebe72b4dad3c2ba3f7023ad47c144e4e473a5"
 dependencies = [
  "atty",
- "bitflags",
+ "bitflags 1.3.2",
- "clap_lex",
+ "clap_lex 0.2.4",
  "indexmap",
  "strsim",
  "termcolor",
  "textwrap 0.16.0",
 ]
 
+[[package]]
+name = "clap"
+version = "4.1.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "42dfd32784433290c51d92c438bb72ea5063797fc3cc9a21a8c4346bebbb2098"
+dependencies = [
+ "bitflags 2.0.2",
+ "clap_derive",
+ "clap_lex 0.3.3",
+ "is-terminal",
+ "once_cell",
+ "strsim",
+ "termcolor",
+]
+
+[[package]]
+name = "clap_derive"
+version = "4.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fddf67631444a3a3e3e5ac51c36a5e01335302de677bd78759eaa90ab1f46644"
+dependencies = [
+ "heck",
+ "proc-macro-error",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "clap_lex"
 version = "0.2.4"
@@ -449,6 +483,15 @@ dependencies = [
  "os_str_bytes",
 ]
 
+[[package]]
+name = "clap_lex"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "033f6b7a4acb1f358c742aaca805c939ee73b4c6209ae4318ec7aca81c42e646"
+dependencies = [
+ "os_str_bytes",
+]
+
 [[package]]
 name = "cli_utils"
 version = "0.0.1"
@@ -493,7 +536,7 @@ version = "0.24.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f425db7937052c684daec3bd6375c8abe2d146dca4b8b143d6db777c39138f3a"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "block",
  "cocoa-foundation",
  "core-foundation 0.9.3",
@@ -509,7 +552,7 @@ version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7ade49b65d560ca58c403a479bb396592b155c0185eada742ee323d1d68d6318"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "block",
  "core-foundation 0.9.3",
  "core-graphics-types",
@@ -656,7 +699,7 @@ version = "0.19.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b3889374e6ea6ab25dba90bb5d96202f61108058361f6dc72e8b03e6f8bbe923"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "core-foundation 0.7.0",
  "foreign-types",
  "libc",
@@ -668,7 +711,7 @@ version = "0.22.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2581bbab3b8ffc6fcbd550bf46c355135d16e9ff2a6ea032ad6b9bf1d7efe4fb"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "core-foundation 0.9.3",
  "core-graphics-types",
  "foreign-types",
@@ -681,7 +724,7 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3a68b68b3446082644c91ac778bf50cd4104bfb002b5a6a7c44cca5a2c70788b"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "core-foundation 0.9.3",
  "foreign-types",
  "libc",
@@ -881,7 +924,7 @@ version = "0.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2daefd788d1e96e0a9d66dee4b828b883509bc3ea9ce30665f04c3246372690c"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "libloading",
  "winapi",
 ]
@@ -1134,7 +1177,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8ef1a30ae415c3a691a4f41afddc2dbcd6d70baf338368d85ebc1e8ed92cedb9"
 dependencies = [
  "cfg-if 1.0.0",
- "rustix",
+ "rustix 0.36.9",
  "windows-sys 0.45.0",
 ]
 
@@ -1419,7 +1462,7 @@ version = "0.5.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7fc59e5f710e310e76e6707f86c561dd646f69a8876da9131703b2f717de818d"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "gpu-alloc-types",
 ]
 
@@ -1429,7 +1472,7 @@ version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "54804d0d6bc9d7f26db4eaec1ad10def69b599315f487d32c334a80d1efe67a5"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
 ]
 
 [[package]]
@@ -1438,7 +1481,7 @@ version = "0.2.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0b0c02e1ba0bdb14e965058ca34e09c020f8e507a760df1121728e0aef68d57a"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "gpu-descriptor-types",
  "hashbrown 0.12.3",
 ]
@@ -1449,7 +1492,7 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "363e3677e55ad168fef68cf9de3a4a310b53124c5e784c53a1d70e92d23f2126"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
 ]
 
 [[package]]
@@ -1520,6 +1563,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "hermit-abi"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fed44880c466736ef9a5c5b5facefb5ed0785676d0c02d612db14e54f0d84286"
+
 [[package]]
 name = "hexf-parse"
 version = "0.2.1"
@@ -1745,6 +1794,18 @@ version = "2.7.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "30e22bd8629359895450b59ea7a776c850561b96a3b1d31321c1949d9e6c9146"
 
+[[package]]
+name = "is-terminal"
+version = "0.4.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "256017f749ab3117e93acb91063009e1f1bb56d03965b14c2c8df4eb02c524d8"
+dependencies = [
+ "hermit-abi 0.3.1",
+ "io-lifetimes",
+ "rustix 0.37.3",
+ "windows-sys 0.45.0",
+]
+
 [[package]]
 name = "itertools"
 version = "0.9.0"
@@ -1848,6 +1909,17 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "libtest-mimic"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d7b603516767d1ab23d0de09d023e62966c3322f7148297c35cf3d97aa8b37fa"
+dependencies = [
+ "clap 4.1.11",
+ "termcolor",
+ "threadpool",
+]
+
 [[package]]
 name = "linked-hash-map"
 version = "0.5.6"
@@ -1860,6 +1932,12 @@ version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f051f77a7c8e6957c0696eac88f26b0117e54f52d3fc682ab19397a8812846a4"
 
+[[package]]
+name = "linux-raw-sys"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d59d8c75012853d2e872fb56bc8a2e53718e2cafe1a4c823143141c6d90c322f"
+
 [[package]]
 name = "llvm-sys"
 version = "130.0.7"
@@ -1898,7 +1976,7 @@ version = "0.1.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8b6f2d7176b94027af58085a2c9d27c4e416586caba409c314569213901d6068"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "byteorder",
  "lazy_static",
  "libc",
@@ -1980,7 +2058,7 @@ version = "0.23.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e0514f491f4cc03632ab399ee01e2c1c1b12d3e1cf2d667c1ff5f87d6dcd2084"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "block",
  "core-graphics-types",
  "foreign-types",
@@ -2048,7 +2126,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3012f2dbcc79e8e0b5825a4836a7106a75dd9b2fe42c528163be0f572538c705"
 dependencies = [
  "bit-set",
- "bitflags",
+ "bitflags 1.3.2",
  "codespan-reporting",
  "hexf-parse",
  "indexmap",
@@ -2065,7 +2143,7 @@ version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "96d868f654c72e75f8687572699cdabe755f03effbb62542768e995d5b8d699d"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "jni-sys",
  "ndk-sys",
  "num_enum",
@@ -2127,7 +2205,7 @@ version = "0.22.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e4916f159ed8e5de0082076562152a76b7a1f64a01fd9d1e0fea002c37624faf"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "cc",
  "cfg-if 1.0.0",
  "libc",
@@ -2140,7 +2218,7 @@ version = "0.23.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8f3790c00a0150112de0f4cd161e3d7fc4b2d8a5542ffc35f099a2562aecb35c"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "cc",
  "cfg-if 1.0.0",
  "libc",
@@ -2153,7 +2231,7 @@ version = "0.24.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fa52e972a9a719cecb6864fb88568781eb706bac2cd1d4f04a648542dbf78069"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "cfg-if 1.0.0",
  "libc",
  "memoffset 0.6.5",
@@ -2165,7 +2243,7 @@ version = "0.26.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bfdda3d196821d6af13126e40375cdf7da646a96114af134d5f417a9a1dc8e1a"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "cfg-if 1.0.0",
  "libc",
  "static_assertions",
@@ -2646,6 +2724,30 @@ dependencies = [
  "toml_edit",
 ]
 
+[[package]]
+name = "proc-macro-error"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da25490ff9892aab3fcf7c36f08cfb902dd3e71ca0f9f9517bea02a73a5ce38c"
+dependencies = [
+ "proc-macro-error-attr",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "version_check",
+]
+
+[[package]]
+name = "proc-macro-error-attr"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1be40180e52ecc98ad80b184934baf3d0d29f979574e439af5a55274b35f869"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "version_check",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.51"
@@ -2668,7 +2770,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "29f1b898011ce9595050a68e60f90bad083ff2987a695a42357134c8381fba70"
 dependencies = [
  "bit-set",
- "bitflags",
+ "bitflags 1.3.2",
  "byteorder",
  "lazy_static",
  "num-traits",
@@ -2688,7 +2790,7 @@ version = "0.9.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2d9cc634bc78768157b5cbfe988ffcd1dcba95cd2b2f03a88316c08c6d00ed63"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "memchr",
  "unicase",
 ]
@@ -2843,7 +2945,7 @@ version = "0.2.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fb5a58c1855b4b6819d59012155603f0b22ad30cad752600aadfcb695265519a"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
 ]
 
 [[package]]
@@ -3817,6 +3919,7 @@ dependencies = [
  "indoc",
  "insta",
  "lazy_static",
+ "libtest-mimic",
  "pretty_assertions",
  "regex",
  "roc_builtins",
@@ -3915,7 +4018,7 @@ dependencies = [
 name = "roc_unify"
 version = "0.0.1"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "roc_collections",
  "roc_debug_flags",
  "roc_error_macros",
@@ -3971,11 +4074,25 @@ version = "0.36.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fd5c6ff11fecd55b40746d1995a02f2eb375bf8c00d192d521ee09f42bef37bc"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "errno 0.2.8",
  "io-lifetimes",
  "libc",
- "linux-raw-sys",
+ "linux-raw-sys 0.1.4",
+ "windows-sys 0.45.0",
+]
+
+[[package]]
+name = "rustix"
+version = "0.37.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "62b24138615de35e32031d041a09032ef3487a616d901ca4db224e7d557efae2"
+dependencies = [
+ "bitflags 1.3.2",
+ "errno 0.3.0",
+ "io-lifetimes",
+ "libc",
+ "linux-raw-sys 0.3.1",
  "windows-sys 0.45.0",
 ]
 
@@ -4023,7 +4140,7 @@ name = "rustyline"
 version = "9.1.1"
 source = "git+https://github.com/roc-lang/rustyline?rev=e74333c#e74333c0d618896b88175bf06645108f996fe6d0"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "cfg-if 1.0.0",
  "clipboard-win 4.5.0",
  "dirs-next",
@@ -4315,7 +4432,7 @@ version = "0.15.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8a28f16a97fa0e8ce563b2774d1e732dd5d4025d2772c5dba0a41a0f90a29da3"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "calloop",
  "dlib",
  "lazy_static",
@@ -4334,7 +4451,7 @@ version = "0.16.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f307c47d32d2715eb2e0ece5589057820e0e5e70d07c247d1063e844e107f454"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "dlib",
  "lazy_static",
  "log",
@@ -4401,7 +4518,7 @@ version = "0.2.0+1.5.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "246bfa38fe3db3f1dfc8ca5a2cdeb7348c78be2112740cc0ec8ef18b6d94f830"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "num-traits",
 ]
 
@@ -5225,7 +5342,7 @@ version = "0.29.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3f3b068c05a039c9f755f881dc50f01732214f5685e379829759088967c46715"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "downcast-rs",
  "libc",
  "nix 0.24.3",
@@ -5264,7 +5381,7 @@ version = "0.29.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b950621f9354b322ee817a23474e479b34be96c2e909c14f7bc0100e9a970bc6"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "wayland-client",
  "wayland-commons",
  "wayland-scanner",
@@ -5349,7 +5466,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c4688c000eb841ca55f7b35db659b78d6e1cd77d7caf8fb929f4e181f754047d"
 dependencies = [
  "arrayvec 0.7.2",
- "bitflags",
+ "bitflags 1.3.2",
  "cfg_aliases",
  "codespan-reporting",
  "copyless",
@@ -5374,7 +5491,7 @@ dependencies = [
  "arrayvec 0.7.2",
  "ash",
  "bit-set",
- "bitflags",
+ "bitflags 1.3.2",
  "block",
  "core-graphics-types",
  "d3d12",
@@ -5409,7 +5526,7 @@ version = "0.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "549533d9e1cdd4b4cda7718d33ff500fc4c34b5467b71d76b547ae0324f3b2a2"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
 ]
 
 [[package]]
@@ -5551,7 +5668,7 @@ version = "0.26.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9b43cc931d58b99461188607efd7acb2a093e65fc621f54cad78517a6063e73a"
 dependencies = [
- "bitflags",
+ "bitflags 1.3.2",
  "cocoa",
  "core-foundation 0.9.3",
  "core-graphics 0.22.3",

Cargo.toml

@@ -112,6 +112,7 @@ lazy_static = "1.4.0"
 libc = "0.2.139" # update roc_std/Cargo.toml on change
 libfuzzer-sys = "0.4"
 libloading = "0.7.4"
+libtest-mimic = "0.6.0"
 log = "0.4.17"
 mach_object = "0.1"
 maplit = "1.0.2"

crates/compiler/solve/Cargo.toml

@@ -49,3 +49,4 @@ lazy_static.workspace = true
 pretty_assertions.workspace = true
 regex.workspace = true
 tempfile.workspace = true
+libtest-mimic.workspace = true

crates/compiler/solve/tests/uitest.rs

@@ -1 +1,152 @@
-fn main() {}
+use std::{
+    error::Error,
+    ffi::OsStr,
+    fs, io,
+    path::{Path, PathBuf},
+    process::Command,
+};
+
+use lazy_static::lazy_static;
+use libtest_mimic::{run, Arguments, Failed, Trial};
+use regex::Regex;
+use test_solve_helpers::InferOptions;
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let args = Arguments::from_args();
+
+    let test_files = collect_uitest_files()?;
+    let tests = test_files
+        .into_iter()
+        .map(into_test)
+        .collect::<Result<_, _>>()?;
+
+    run(&args, tests).exit()
+}
+
+lazy_static! {
+    static ref UITEST_PATH: PathBuf = PathBuf::from(std::env!("ROC_WORKSPACE_DIR"))
+        .join("crates")
+        .join("compiler")
+        .join("solve")
+        .join("tests")
+        .join("uitest");
+
+    /// # +opt infer:<opt>
+    static ref RE_OPT_INFER: Regex =
+        Regex::new(r#"# +opt infer:(?P<opt>.*)"#).unwrap();
+}
+
+fn collect_uitest_files() -> io::Result<Vec<PathBuf>> {
+    let mut tests = Vec::with_capacity(200);
+
+    let mut dirs_to_visit = vec![UITEST_PATH.clone()];
+    while let Some(dir) = dirs_to_visit.pop() {
+        for entry in fs::read_dir(dir)? {
+            let entry = entry?;
+            let path = entry.path();
+            let entry_type = entry.file_type()?;
+            if entry_type.is_dir() {
+                dirs_to_visit.push(path);
+                continue;
+            }
+
+            if path.extension() == Some(OsStr::new("txt")) {
+                tests.push(path);
+            }
+        }
+    }
+
+    Ok(tests)
+}
+
+fn into_test(path: PathBuf) -> io::Result<Trial> {
+    let name = path
+        .strip_prefix(UITEST_PATH.as_path().parent().unwrap())
+        .expect("collected path does not have uitest prefix")
+        .display()
+        .to_string();
+
+    let trial = Trial::test(name, move || run_test(path));
+    Ok(trial)
+}
+
+fn run_test(path: PathBuf) -> Result<(), Failed> {
+    let data = std::fs::read_to_string(&path)?;
+    let TestCase {
+        infer_options,
+        source,
+    } = TestCase::parse(data)?;
+
+    fs::write(&path, &source)?;
+    check_for_changes(&path)?;
+
+    Ok(())
+}
+
+const UITEST_HEADER: &str = "# uitest:";
+
+struct TestCase {
+    infer_options: InferOptions,
+    source: String,
+}
+
+impl TestCase {
+    fn parse(mut data: String) -> Result<Self, Failed> {
+        // Drop anything following `# uitest:` header lines; that's the output.
+        if let Some(drop_at) = data.find(UITEST_HEADER) {
+            data.truncate(drop_at);
+            data.truncate(data.trim_end().len());
+        }
+
+        Ok(TestCase {
+            infer_options: Self::parse_infer_options(&data)?,
+            source: data,
+        })
+    }
+
+    fn parse_infer_options(data: &str) -> Result<InferOptions, Failed> {
+        let mut infer_opts = InferOptions::default();
+
+        let found_infer_opts = RE_OPT_INFER.captures_iter(data);
+        for infer_opt in found_infer_opts {
+            let opt = infer_opt.name("opt").unwrap().as_str();
+            match opt {
+                "allow_errors" => infer_opts.allow_errors = true,
+                "print_only_under_alias" => infer_opts.print_only_under_alias = true,
+                other => return Err(format!("unknown infer option: {other}").into()),
+            }
+        }
+
+        Ok(infer_opts)
+    }
+}
+
+fn check_for_changes(path: &Path) -> Result<(), Failed> {
+    let is_tracked = Command::new("git")
+        .args(["ls-files", "--error-unmatch"])
+        .arg(path)
+        .output()?;
+
+    if !is_tracked.status.success() {
+        return Err(format!(
+            "Test file {} is not tracked by git. Try using `git add` on it.",
+            path.display(),
+        )
+        .into());
+    }
+
+    let has_changes = Command::new("git")
+        .args(["diff", "--color=always"])
+        .arg(path)
+        .output()?;
+
+    if !has_changes.stdout.is_empty() {
+        return Err(format!(
+            "{}\nOutput has changed. If it looks okay, `git` add the file.",
+            std::str::from_utf8(&has_changes.stdout)?
+        )
+        .into());
+    }
+
+    Ok(())
+}