fix(fmt): --check was broken for CSS, YAML and HTML (#25848)

`deno fmt --check` was broken for CSS, YAML and HTML files.

Before this PR, formatting any of these file types would return a
string, even though the contract in `cli/tools/fmt.rs` is to only return a
string if the formatting changed. This causes wrong flagging of these files
as being badly formatted even though diffs showed nothing (because
they were in fact formatted properly).

Closes https://github.com/denoland/deno/issues/25840

cli/tools/fmt.rs

@@ -297,12 +297,7 @@ fn format_markdown(
               Ok(None)
             }
           }
-          "yml" | "yaml" => pretty_yaml::format_text(
-            text,
-            &get_resolved_yaml_config(fmt_options),
-          )
-          .map(Some)
-          .map_err(AnyError::from),
+          "yml" | "yaml" => format_yaml(text, fmt_options),
           _ => {
             let mut codeblock_config =
               get_resolved_typescript_config(fmt_options);
@@ -339,13 +334,33 @@ pub fn format_css(
   file_text: &str,
   fmt_options: &FmtOptionsConfig,
 ) -> Result<Option<String>, AnyError> {
-  malva::format_text(
+  let formatted_str = malva::format_text(
     file_text,
     malva::detect_syntax(file_path).unwrap_or(malva::Syntax::Css),
     &get_resolved_malva_config(fmt_options),
   )
-  .map(Some)
-  .map_err(AnyError::from)
+  .map_err(AnyError::from)?;
+
+  Ok(if formatted_str == file_text {
+    None
+  } else {
+    Some(formatted_str)
+  })
+}
+
+fn format_yaml(
+  file_text: &str,
+  fmt_options: &FmtOptionsConfig,
+) -> Result<Option<String>, AnyError> {
+  let formatted_str =
+    pretty_yaml::format_text(file_text, &get_resolved_yaml_config(fmt_options))
+      .map_err(AnyError::from)?;
+
+  Ok(if formatted_str == file_text {
+    None
+  } else {
+    Some(formatted_str)
+  })
 }
 
 pub fn format_html(
@@ -353,7 +368,7 @@ pub fn format_html(
   file_text: &str,
   fmt_options: &FmtOptionsConfig,
 ) -> Result<Option<String>, AnyError> {
-  markup_fmt::format_text(
+  let format_result = markup_fmt::format_text(
     file_text,
     markup_fmt::detect_language(file_path)
       .unwrap_or(markup_fmt::Language::Html),
@@ -419,7 +434,6 @@ pub fn format_html(
       }
     },
   )
-  .map(Some)
   .map_err(|error| match error {
     markup_fmt::FormatError::Syntax(error) => AnyError::from(error),
     markup_fmt::FormatError::External(errors) => {
@@ -438,6 +452,14 @@ pub fn format_html(
           .collect::<String>(),
       )
     }
+  });
+
+  let formatted_str = format_result?;
+
+  Ok(if formatted_str == file_text {
+    None
+  } else {
+    Some(formatted_str)
   })
 }
 
@@ -469,12 +491,7 @@ pub fn format_file(
         Ok(None)
       }
     }
-    "yml" | "yaml" => pretty_yaml::format_text(
-      file_text,
-      &get_resolved_yaml_config(fmt_options),
-    )
-    .map(Some)
-    .map_err(AnyError::from),
+    "yml" | "yaml" => format_yaml(file_text, fmt_options),
     "ipynb" => dprint_plugin_jupyter::format_text(
       file_text,
       |file_path: &Path, file_text: String| {

tests/specs/fmt/css/__test__.jsonc

@@ -1,5 +1,13 @@
 {
   "tempDir": true,
-  "args": "fmt",
+  "tests": {
+    "badly_formatted": {
+      "args": "fmt badly_formatted.css",
       "output": "[WILDLINE]badly_formatted.css\nChecked 1 file\n"
+    },
+    "well_formatted": {
+      "args": "fmt --check well_formatted.css",
+      "output": "Checked 1 file\n"
+    }
+  }
 }

tests/specs/fmt/css/well_formatted.css

@@ -0,0 +1,3 @@
+#app > .btn {
+  color: #000;
+}

tests/specs/fmt/html/__test__.jsonc

@@ -1,5 +1,13 @@
 {
   "tempDir": true,
-  "args": "fmt --unstable-html",
+  "tests": {
+    "badly_formatted": {
+      "args": "fmt badly_formatted.html",
       "output": "[WILDLINE]badly_formatted.html\nChecked 1 file\n"
+    },
+    "well_formatted": {
+      "args": "fmt --check well_formatted.html",
+      "output": "Checked 1 file\n"
+    }
+  }
 }

tests/specs/fmt/html/well_formatted.html

@@ -0,0 +1,11 @@
+<div class="container">content</div>
+
+<script>
+  let counter = 0;
+</script>
+
+<style>
+  .container {
+    padding: 8px;
+  }
+</style>

tests/specs/fmt/yaml/__test__.jsonc

@@ -1,5 +1,13 @@
 {
   "tempDir": true,
-  "args": "fmt",
+  "tests": {
+    "badly_formatted": {
+      "args": "fmt badly_formatted.yml",
       "output": "[WILDLINE]badly_formatted.yml\nChecked 1 file\n"
+    },
+    "well_formatted": {
+      "args": "fmt --check well_formatted.yml",
+      "output": "Checked 1 file\n"
+    }
+  }
 }

tests/specs/fmt/yaml/well_formatted.yml

@@ -0,0 +1,3 @@
+- Test
+- Test
+- Test