Only set language_used after a full syntactic diff

This fixes cases where the language is detected but the file hits the
byte limit.

Fixes #462.

CHANGELOG.md

@@ -4,6 +4,11 @@
 
 Improved CSS parsing and HTML sublanguage parsing.
 
+### Display
+
+Fixed an issue with unwanted underlines with textual diffing when
+DFT_BYTE_LIMIT is reached.
+
 ### Build
 
 Renamed the vendored parser directory to vendored_parsers/, as `cargo

sample_files/compare.expected

@@ -71,7 +71,7 @@ sample_files/html_simple_before.html sample_files/html_simple_after.html
 ce3bfa12bc21d0eb5528766e18387e86  -
 
 sample_files/huge_cpp_before.cpp sample_files/huge_cpp_after.cpp
-5ce6b92e727e0cd4cb2bf40272c4b952  -
+8910dbf7dae13b1a7229b0497602b414  -
 
 sample_files/identical_before.scala sample_files/identical_after.scala
 9c7319f61833e46a0a8cb6c01cc997c9  -

src/main.rs

@@ -297,7 +297,7 @@ fn diff_file_content(
                 lhs_display_path: lhs_display_path.into(),
                 rhs_display_path: rhs_display_path.into(),
                 display_language: None,
-                detected_language: None,
+                language_used: None,
                 lhs_src: FileContent::Binary,
                 rhs_src: FileContent::Binary,
                 lhs_positions: vec![],
@@ -326,7 +326,7 @@ fn diff_file_content(
         FileArgument::DevNull => (&lhs_src, Path::new(&lhs_display_path)),
     };
 
-    let mut language = language_override.or_else(|| guess(guess_path, guess_src));
+    let language = language_override.or_else(|| guess(guess_path, guess_src));
     let lang_config = language.map(tsp::from_language);
 
     if lhs_bytes == rhs_bytes {
@@ -336,7 +336,7 @@ fn diff_file_content(
             lhs_display_path: lhs_display_path.into(),
             rhs_display_path: rhs_display_path.into(),
             display_language: language.map(|l| language_name(l).into()),
-            detected_language: language,
+            language_used: language,
             lhs_src: FileContent::Text("".into()),
             rhs_src: FileContent::Text("".into()),
             lhs_positions: vec![],
@@ -347,6 +347,7 @@ fn diff_file_content(
         };
     }
 
+    let mut language_used = None;
     let (lang_name, lhs_positions, rhs_positions) = match lang_config {
         _ if lhs_bytes.len() > diff_options.byte_limit
             || rhs_bytes.len() > diff_options.byte_limit =>
@@ -370,11 +371,12 @@ fn diff_file_content(
                 let lang_name = language.map(|l| language_name(l).into());
                 let has_syntactic_changes = lhs != rhs;
 
+                language_used = language;
                 return DiffResult {
                     lhs_display_path: lhs_display_path.into(),
                     rhs_display_path: rhs_display_path.into(),
                     display_language: lang_name,
-                    detected_language: language,
+                    language_used,
                     lhs_src: FileContent::Text(lhs_src),
                     rhs_src: FileContent::Text(rhs_src),
                     lhs_positions: vec![],
@@ -415,13 +417,13 @@ fn diff_file_content(
             if exceeded_graph_limit {
                 let lhs_positions = line_parser::change_positions(&lhs_src, &rhs_src);
                 let rhs_positions = line_parser::change_positions(&rhs_src, &lhs_src);
-                language = None;
                 (
                     Some("Text (exceeded DFT_GRAPH_LIMIT)".into()),
                     lhs_positions,
                     rhs_positions,
                 )
             } else {
+                language_used = language;
                 // TODO: Make this .expect() unnecessary.
                 let language =
                     language.expect("If we had a ts_lang, we must have guessed the language");
@@ -462,7 +464,7 @@ fn diff_file_content(
         lhs_display_path: lhs_display_path.into(),
         rhs_display_path: rhs_display_path.into(),
         display_language: lang_name,
-        detected_language: language,
+        language_used,
         lhs_src: FileContent::Text(lhs_src),
         rhs_src: FileContent::Text(rhs_src),
         lhs_positions,
@@ -578,7 +580,7 @@ fn print_diff_result(display_options: &DisplayOptions, summary: &DiffResult) {
                         &summary.lhs_display_path,
                         &summary.rhs_display_path,
                         &display_language,
-                        summary.detected_language,
+                        summary.language_used,
                     );
                 }
                 DisplayMode::SideBySide | DisplayMode::SideBySideShowBoth => {
@@ -588,7 +590,7 @@ fn print_diff_result(display_options: &DisplayOptions, summary: &DiffResult) {
                         &summary.lhs_display_path,
                         &summary.rhs_display_path,
                         &display_language,
-                        summary.detected_language,
+                        summary.language_used,
                         lhs_src,
                         rhs_src,
                         &summary.lhs_positions,

src/summary.rs

@@ -13,7 +13,7 @@ pub struct DiffResult {
     pub lhs_display_path: String,
     pub rhs_display_path: String,
     pub display_language: Option<String>,
-    pub detected_language: Option<crate::parse::guess_language::Language>,
+    pub language_used: Option<crate::parse::guess_language::Language>,
     pub lhs_src: FileContent,
     pub rhs_src: FileContent,
     pub hunks: Vec<Hunk>,