On tests that specify --color=always emit SVG file with stderr output

Leverage `anstyle-svg`, as `cargo` does now, to emit `.svg` files instead of `.stderr` files for tests that explicitly enable color output. This will make reviewing changes to the graphical output of tests much more human friendly.

src/tools/compiletest/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2021"
 doctest = false
 
 [dependencies]
+anstyle-svg = "0.1.3"
 colored = "2"
 diff = "0.1.10"
 unified-diff = "0.2.1"

src/tools/compiletest/src/common.rs

@@ -703,6 +703,7 @@ pub fn expected_output_path(
 }
 
 pub const UI_EXTENSIONS: &[&str] = &[
+    UI_SVG,
     UI_STDERR,
     UI_STDOUT,
     UI_FIXED,
@@ -714,6 +715,7 @@ pub const UI_EXTENSIONS: &[&str] = &[
     UI_COVERAGE,
     UI_COVERAGE_MAP,
 ];
+pub const UI_SVG: &str = "svg";
 pub const UI_STDERR: &str = "stderr";
 pub const UI_STDOUT: &str = "stdout";
 pub const UI_FIXED: &str = "fixed";

src/tools/compiletest/src/runtest.rs

@@ -1,6 +1,6 @@
 // ignore-tidy-filelength
 
-use crate::common::{expected_output_path, UI_EXTENSIONS, UI_FIXED, UI_STDERR, UI_STDOUT};
+use crate::common::{expected_output_path, UI_EXTENSIONS, UI_FIXED, UI_STDERR, UI_STDOUT, UI_SVG};
 use crate::common::{incremental_dir, output_base_dir, output_base_name, output_testname_unique};
 use crate::common::{Assembly, Incremental, JsDocTest, MirOpt, RunMake, RustdocJson, Ui};
 use crate::common::{Codegen, CodegenUnits, DebugInfo, Debugger, Rustdoc};
@@ -4014,9 +4014,17 @@ impl<'test> TestCx<'test> {
         explicit_format: bool,
     ) -> usize {
         let stderr_bits = format!("{}bit.stderr", self.config.get_pointer_width());
+        let force_color_svg = self.props.compile_flags.iter().any(|s| s.contains("--color"))
+            && !self.config.target.contains("windows");
         let (stderr_kind, stdout_kind) = match output_kind {
             TestOutput::Compile => (
-                { if self.props.stderr_per_bitwidth { &stderr_bits } else { UI_STDERR } },
+                if force_color_svg {
+                    UI_SVG
+                } else if self.props.stderr_per_bitwidth {
+                    &stderr_bits
+                } else {
+                    UI_STDERR
+                },
                 UI_STDOUT,
             ),
             TestOutput::Run => (UI_RUN_STDERR, UI_RUN_STDOUT),
@@ -4051,7 +4059,9 @@ impl<'test> TestCx<'test> {
             _ => {}
         };
 
-        let stderr = if explicit_format {
+        let stderr = if force_color_svg {
+            anstyle_svg::Term::new().render_svg(&proc_res.stderr)
+        } else if explicit_format {
             proc_res.stderr.clone()
         } else {
             json::extract_rendered(&proc_res.stderr)