Implement inline ANSI highlighting in summary.

Author: bjacotg

googletest/src/matcher_support/line_style.rs

@@ -0,0 +1,154 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Utilities to style matcher explanation message with ANSI formatting.
+
+use std::fmt::Display;
+use std::io::IsTerminal;
+
+
+/// Environment variable controlling the usage of ansi color in difference
+/// summary.
+pub(crate) const NO_COLOR_VAR: &str = "GTEST_RUST_NO_COLOR";
+
+// Use ANSI code to enable styling on the summary lines.
+//
+// See https://en.wikipedia.org/wiki/ANSI_escape_code.
+pub(crate) struct LineStyle {
+    ansi_prefix: &'static str,
+    ansi_suffix: &'static str,
+    highlighted_prefix: &'static str,
+    header: char,
+}
+
+impl LineStyle {
+    // Font in red and bold
+    pub(crate) fn extra_actual_style() -> Self {
+        Self {
+            ansi_prefix: "\x1B[1;31m",
+            ansi_suffix: "\x1B[0m",
+            highlighted_prefix: "",
+            header: '-',
+        }
+    }
+
+    // Font in green and bold
+    pub(crate) fn extra_expected_style() -> Self {
+        Self {
+            ansi_prefix: "\x1B[1;32m",
+            ansi_suffix: "\x1B[0m",
+            highlighted_prefix: "",
+            header: '+',
+        }
+    }
+
+    // Font in italic
+    pub(crate) fn comment_style() -> Self {
+        Self { ansi_prefix: "\x1B[3m", ansi_suffix: "\x1B[0m", highlighted_prefix: "", header: ' ' }
+    }
+
+    // No ansi styling
+    pub(crate) fn unchanged_style() -> Self {
+        Self { ansi_prefix: "", ansi_suffix: "", highlighted_prefix: "", header: ' ' }
+    }
+
+    pub(crate) fn style(self, line: &str) -> impl Display + '_ {
+        StyledLine { style: self, line }
+    }
+
+    pub(crate) fn style_highlighted(self, line: HighlightedString) -> impl Display {
+        StyledLineWithHighlight { style: self, line }
+    }
+}
+
+struct StyledLine<'a> {
+    style: LineStyle,
+    line: &'a str,
+}
+
+impl<'a> Display for StyledLine<'a> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        if stdout_supports_color() {
+            write!(
+                f,
+                "{}{}{}{}",
+                self.style.header, self.style.ansi_prefix, self.line, self.style.ansi_suffix
+            )
+        } else {
+            write!(f, "{}{}", self.style.header, self.line)
+        }
+    }
+}
+struct StyledLineWithHighlight {
+    style: LineStyle,
+    line: HighlightedString,
+}
+
+impl Display for StyledLineWithHighlight {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.style.header)?;
+        for (piece, highlight) in &self.line.0 {
+            if ! stdout_supports_color() {
+                write!(f, "{}", piece)?;
+            } else if *highlight {
+                write!(f, "{}{}{}", self.style.highlighted_prefix, piece, self.style.ansi_suffix)?;
+            } else {
+                write!(f, "{}{}{}", self.style.ansi_prefix, piece, self.style.ansi_suffix)?;
+            }
+        }
+        Ok(())
+    }
+}
+
+pub(crate) struct HighlightedString(Vec<(String, bool)>);
+
+impl HighlightedString {
+    pub(crate) fn new() -> Self {
+        Self(vec![])
+    }
+
+    pub(crate) fn push_highlighted(&mut self, c: char) {
+        match self.0.last_mut() {
+            Some((s, true)) => s.push(c),
+            _ => self.0.push((c.to_string(), true)),
+        }
+    }
+
+    pub(crate) fn push(&mut self, c: char) {
+        match self.0.last_mut() {
+            Some((s, false)) => s.push(c),
+            _ => self.0.push((c.to_string(), false)),
+        }
+    }
+}
+
+
+
+#[rustversion::since(1.70)]
+fn stdout_supports_color() -> bool {
+    match (is_env_var_set("NO_COLOR"), is_env_var_set("FORCE_COLOR")) {
+        (true, _) => false,
+        (false, true) => true,
+        (false, false) => std::io::stdout().is_terminal(),
+    }
+}
+
+#[rustversion::not(since(1.70))]
+fn stdout_supports_color() -> bool {
+    is_env_var_set("FORCE_COLOR")
+}
+
+fn is_env_var_set(var: &'static str) -> bool {
+    std::env::var(var).map(|s| !s.is_empty()).unwrap_or(false)
+}

googletest/src/matcher_support/mod.rs

@@ -21,5 +21,6 @@
 pub(crate) mod count_elements;
 pub mod description;
 pub(crate) mod edit_distance;
+pub(crate) mod line_style;
 pub(crate) mod summarize_diff;
 pub(crate) mod zipped_iterator;