Add insta-based snapshot tests that cover side-by-side format

I'm going to fix inline diff issue #704, and found that the inline format isn't
covered by CLI tests. I could duplicate compare_all.sh to test various formats,
but it's uneasy to review that a new formatting is better than the previous
version. I think snapshot testing will help guarantee the output quality without
increasing maintenance burden too much.

If we like the idea, maybe we can migrate some of compare_all.sh tests to the
insta-based ones.

Note that this will add ~10sec to "cargo test" runs.

.gitignore

@@ -5,5 +5,6 @@ flamegraph.svg
 .idea
 
 sample_files/compare.result
+tests/snapshots/*.snap.new
 
 notes.md

manual/src/adding_a_parser.md

@@ -139,6 +139,15 @@ $ ./sample_files/compare_all.sh
 $ cp sample_files/compare.result sample_files/compare.expected
 ```
 
+Run the CLI test and [update the snapshots][insta] as well.
+
+```
+$ cargo insta test
+$ cargo insta accept
+```
+
+[insta]: https://insta.rs/docs/quickstart/#reviewing-snapshots
+
 ## Maintenance
 
 To update a parser that is already imported, use `git subtree pull`.

tests/cli.rs

@@ -1,4 +1,5 @@
 use std::process::Command;
+use std::str;
 
 use assert_cmd::prelude::*;
 use predicates::prelude::*;
@@ -259,3 +260,50 @@ fn walk_hidden_items() {
             .and(predicate::str::contains("after"));
     cmd.assert().stdout(predicate_fn);
 }
+
+const MAX_SAMPLE_FILE_SIZE: u64 = 10_000;
+
+#[test]
+fn samples_side_by_side() {
+    insta::glob!("../sample_files", "*_1.*", |left_file| {
+        let base_dir = left_file.parent().unwrap().parent().unwrap();
+        let file_name = left_file.file_name().unwrap().to_str().unwrap();
+        let right_file = left_file.with_file_name(file_name.replace("_1.", "_2."));
+        // Large sample files are excluded because it's slow to diff with debug
+        // binary, and the snapshot results wouldn't help review changes.
+        if left_file.metadata().unwrap().len() > MAX_SAMPLE_FILE_SIZE
+            || right_file.metadata().unwrap().len() > MAX_SAMPLE_FILE_SIZE
+        {
+            eprintln!("Skipping large sample: {file_name}");
+            return;
+        }
+        // TODO: Fix CI instability on the following architectures:
+        // x86_64-apple-darwin, x86_64-pc-windows-msvc, aarch64-apple-darwin
+        if file_name == "f_sharp_1.fs" {
+            eprintln!("Skipping unstable sample: {file_name}");
+            return;
+        }
+        // TODO: Remove this once the fix gets merged.
+        if file_name == "big_text_hunk_1.txt" {
+            eprintln!("Skipping crash sample: {file_name}");
+            return;
+        }
+
+        let to_path_arg = |path: &Path| {
+            let short_path = path.strip_prefix(base_dir).unwrap();
+            let short_str = short_path.to_str().unwrap();
+            short_str.replace(std::path::MAIN_SEPARATOR, "/")
+        };
+        let mut cmd = get_base_command();
+        let assert = cmd
+            .arg("--color=always")
+            .arg("--display=side-by-side")
+            .arg("--width=160")
+            .arg(to_path_arg(left_file))
+            .arg(to_path_arg(&right_file))
+            .assert()
+            .success();
+        let stdout = str::from_utf8(&assert.get_output().stdout).unwrap();
+        insta::assert_snapshot!(stdout);
+    });
+}

tests/snapshots/cli__samples_side_by_side@Session_1.kt.snap

@@ -0,0 +1,32 @@
+---
+source: tests/cli.rs
+expression: stdout
+input_file: sample_files/Session_1.kt
+---
+sample_files/Session_2.kt --- 1/2 --- Kotlin
+ 96     /**                                                                      96     /**
+ 97      * The session's photo URL.                                              97      * The session's photo URL.
+ 98      */                                                                      98      */
+ 99     val photoUrl: String?,                                                   99     val photoUrl: String,
+100                                                                             100 
+101     /**                                                                     101     /**
+102      * IDs of the sessions related to this session.                         102      * IDs of the sessions related to this session.
+
+sample_files/Session_2.kt --- 2/2 --- Kotlin
+114         return startTime <= now && endTime >= now                           114         return startTime <= now && endTime >= now
+115     }                                                                       115     }
+...                                                                             116 
+...                                                                             117     val hasPhoto inline get() = photoUrl.isNotEmpty()
+116                                                                             118 
+117     /**                                                                     119     /**
+118      * Returns whether the session has a video or not. A session could be l 120      * Returns whether the session has a video or not. A session could be l
+... ive streaming or have a                                                     ... ive streaming or have a
+119      * recorded session. Both live stream and recorded videos are stored in 121      * recorded session. Both live stream and recorded videos are stored in
+...  [Session.youTubeUrl].                                                      ...  [Session.youTubeUrl].
+120      */                                                                     122      */
+121     fun hasVideo() = youTubeUrl.isNotEmpty()                                123     val hasVideo inline get() = youTubeUrl.isNotEmpty()
+...                                                                             124 
+...                                                                             125     val hasPhotoOrVideo inline get() = hasPhoto || hasVideo
+122                                                                             126 
+123     /**                                                                     127     /**
+124      * The year the session was held.                                       128      * The year the session was held.

tests/snapshots/cli__samples_side_by_side@ada_1.adb.snap

@@ -0,0 +1,14 @@
+---
+source: tests/cli.rs
+expression: stdout
+input_file: sample_files/ada_1.adb
+---
+sample_files/ada_2.adb --- Ada
+1  with Ada.Text_IO; use Ada.Text_IO; procedure Hello is begin Put_Line ("Hello 1 with Ada.Text_IO;
+.  WORLD!"); end Hello;                                                         . 
+.                                                                               2 
+.                                                                               3 procedure Hello is
+.                                                                               4   package TIO renames Ada.Text_IO;
+.                                                                               5 begin
+.                                                                               6   TIO.Put_Line ("Hello World!");
+.                                                                               7 end Hello;

tests/snapshots/cli__samples_side_by_side@added_line_1.txt.snap

@@ -0,0 +1,9 @@
+---
+source: tests/cli.rs
+expression: stdout
+input_file: sample_files/added_line_1.txt
+---
+sample_files/added_line_2.txt --- Text
+1 1 potato
+2 2 tomato
+  3 legato

tests/snapshots/cli__samples_side_by_side@align_footer_1.txt.snap

@@ -0,0 +1,10 @@
+---
+source: tests/cli.rs
+expression: stdout
+input_file: sample_files/align_footer_1.txt
+---
+sample_files/align_footer_2.txt --- Text
+1 before                                                                        1 before
+2  foo x                                                                        2  x
+3 y                                                                             . 
+4 after                                                                         3 after

tests/snapshots/cli__samples_side_by_side@all_changed_1.js.snap

@@ -0,0 +1,7 @@
+---
+source: tests/cli.rs
+expression: stdout
+input_file: sample_files/all_changed_1.js
+---
+sample_files/all_changed_2.js --- JavaScript
+1 a                                                                             1 b

tests/snapshots/cli__samples_side_by_side@apex_1.cls.snap

@@ -0,0 +1,7 @@
+---
+source: tests/cli.rs
+expression: stdout
+input_file: sample_files/apex_1.cls
+---
+sample_files/apex_2.cls --- Apex
+No syntactic changes.

tests/snapshots/cli__samples_side_by_side@bad_combine_1.rs.snap

@@ -0,0 +1,33 @@
+---
+source: tests/cli.rs
+expression: stdout
+input_file: sample_files/bad_combine_1.rs
+---
+sample_files/bad_combine_2.rs --- 1/2 --- Rust
+ 1                                                                              . 
+ 2 fn column_widths(                                                            . 
+ 3     hunks: &[Hunk],                                                          . 
+ 4     lhs_mps: &[MatchedPos],                                                  . 
+ 5     rhs_mps: &[MatchedPos],                                                  . 
+ 6     max_lhs_src_line: LineNumber,                                            . 
+ 7     max_rhs_src_line: LineNumber,                                            . 
+ 8 )  {                                                                         . 
+ 9 }                                                                            . 
+10                                                                              . 
+11 fn display_line_nums(                                                        1 fn display_line_nums(
+12 ) -> (String, String) {                                                      2 ) -> (String, String) {
+13     let display_rhs_line_num: String = match rhs_line_num {                  3     let display_rhs_line_num: String = match rhs_line_num {
+14         Some(line_num) => {                                                  4         Some(line_num) => {
+15             let s = format_line_num_padded(line_num, rhs_column_width);      5             let s = format_line_num_padded(line_num, widths.rhs_line_nums);
+16             if rhs_lines_with_novel.contains(&line_num) {                    6             if rhs_lines_with_novel.contains(&line_num) {
+17                 s.bright_green().to_string()                                 7                 s.bright_green().to_string()
+18             } else {                                                         8             } else {
+
+sample_files/bad_combine_2.rs --- 2/2 --- Rust
+21         }                                                                    11         }
+22         None => format_missing_line_num(                                     12         None => format_missing_line_num(
+23             prev_rhs_line_num.unwrap_or_else(|| 10.into()),                  13             prev_rhs_line_num.unwrap_or_else(|| 10.into()),
+24             rhs_column_width,                                                14             widths.rhs_line_nums,
+25         ),                                                                   15         ),
+26     };                                                                       16     };
+27                                                                              17 

tests/snapshots/cli__samples_side_by_side@change_outer_1.el.snap

@@ -0,0 +1,7 @@
+---
+source: tests/cli.rs
+expression: stdout
+input_file: sample_files/change_outer_1.el
+---
+sample_files/change_outer_2.el --- Emacs Lisp
+1 (lhs comma rhs)                                                               1 [(lhs) comma rhs]