Use similar to diff expected and actual output in filetests (#4282)

Cargo.lock

@@ -561,6 +561,7 @@ dependencies = [
  "log",
  "memmap2",
  "num_cpus",
+ "similar",
  "target-lexicon",
  "thiserror",
 ]
@@ -2599,6 +2600,12 @@ dependencies = [
  "rand_core 0.6.3",
 ]
 
+[[package]]
+name = "similar"
+version = "2.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2e24979f63a11545f5f2c60141afe249d4f19f84581ea2138065e400941d83d3"
+
 [[package]]
 name = "slice-group-by"
 version = "0.3.0"

cranelift/filetests/Cargo.toml

@@ -25,3 +25,4 @@ num_cpus = "1.8.0"
 target-lexicon = "0.12"
 thiserror = "1.0.15"
 anyhow = "1.0.32"
+similar = "2.1.0"

cranelift/filetests/src/test_compile.rs

@@ -8,6 +8,7 @@ use cranelift_codegen::binemit::CodeInfo;
 use cranelift_codegen::ir;
 use cranelift_reader::{TestCommand, TestOption};
 use log::info;
+use similar::TextDiff;
 use std::borrow::Cow;
 use std::env;
 
@@ -102,17 +103,15 @@ fn check_precise_output(text: &str, context: &Context) -> Result<()> {
         "compilation of function on line {} does not match\n\
          the text expectation\n\
          \n\
-         expected:\n\
-         {:#?}\n\
-         actual:\n\
-         {:#?}\n\
+         {}\n\
          \n\
          This test assertion can be automatically updated by setting the\n\
          CRANELIFT_TEST_BLESS=1 environment variable when running this test.
          ",
         context.details.location.line_number,
-        expected,
-        actual,
+        TextDiff::from_slices(&expected, &actual)
+            .unified_diff()
+            .header("expected", "actual")
     )
 }