Refactor terminal detection

Introduce a separate TerminalApp struct to abstract terminal detection
separately from terminal capabilities.

Check $TERM before all other environment variables; terminal emulators
always set this variable and if it's something other than
xterm-256colors it's definitely accurate.

Closes GH-230

CHANGELOG.md

@@ -13,8 +13,15 @@ To publish a new release run `scripts/release` from the project directory.
 - Replace `ureq` with `reqwest` (see [GH-229]).
     This implies that the default build now creates a binary linked against the system standard SSL library, i.e. openssl under Linux.
     A fully static build now requires `--no-default-features --features static` for `cargo build`.
+- Terminal detection always checks `$TERM` first and trusts its value if it denotes a specific terminal emulator (see [GH-232]).
+
+### Fixed
+
+- Correctly detect kitty started from iTerm (see [GH-230] and [GH-232]).
 
 [GH-229]: https://github.com/swsnr/mdcat/pull/229
+[GH-230]: https://github.com/swsnr/mdcat/pull/230
+[GH-232]: https://github.com/swsnr/mdcat/pull/232
 
 ## [0.30.3] – 2022-12-01
 

Cargo.toml

@@ -50,6 +50,7 @@ terminal_size = "0.2.3"
 pretty_assertions = "1.3.0"
 lazy_static = "1.4.0"
 glob = "0.3.0"
+temp-env = "0.3.1"
 
 [build-dependencies]
 # To generate completions during build

mdcat.1.adoc

@@ -25,9 +25,21 @@ If invoked as `mdless` automatically use a pager to display the output, see belo
 
 === CommonMark and terminal support
 
-mdcat supports all basic CommonMark syntax plus a few extensions, highlights syntax in code blocks, and shows inline links and even inline images in some terminal emulators.
+mdcat supports all basic CommonMark syntax plus a few extensions, highlights syntax in code blocks, and shows inline links and even inline images in some terminal programs.
 In iTerm2 it also adds jump marks for section headings.
 
+See <<Terminal support>> below for a list of supported terminal programs and their features.
+
+=== Terminal detection
+
+To enable formatting extensions such sa inline images, `mdcat` needs to detect the terminal program, by checking the following environment variables in the gven order:
+
+1. `$TERM`
+2. `$TERM_PROGRAM`
+3. `$TERMINOLOGY`
+
+See <<Environment>> below for a detailed description of each environment variable.
+
 === Pagination
 
 mdcat can render output in a pager; this is the default when run as `mdless`.
@@ -109,15 +121,29 @@ If run as `mdless` or if `--paginate` is given and the pager fails to start mdca
 == Environment
 
 TERM::
-    If this variable is `wezterm`, mdcat assumes that the terminal is WezTerm. By default WezTerm does not set TERM to wezterm but mdcat can still detect it trough TERM_PROGRAM.
-    If this variable is `xterm-kitty`, mdcat assumes that the terminal is Kitty.
+
+    `mdcat` first checks this variable to identify the terminal program (see <<Terminal detection>>).
+It understands the following values.
++
+    * `wezterm`: WezTerm.  Note that WezTerm sets `$TERM` to `xterm-256color` by default, and only uses `wezterm` for `$TERM` if explicitly configured to do so.
+    * `xterm-kitty`: Kitty
++
+For all other values `mdcat` proceeds to check `$TERM_PROGRAM`.
 
 TERM_PROGRAM::
-    If this variable is `iTerm.app`, mdcat assumes that the terminal is iTerm2.
-    If this variable is `WezTerm`, mdcat assumes that the terminal is WezTerm.
+
+    If `$TERM` does not conclusively identify the terminal program `mdcat` checks this variable next. It understands the following values:
++
+    * `iTerm.app`: iTerm2
+    * `WezTerm`: WezTerm
++
+For all other values `mdcat` proceeds to check `$TERMINOLOGY`.
 
 TERMINOLOGY::
+
     If this variable is `1`, mdcat assumes that the terminal is Terminology.
++
+Otherwise `mdcat` ends terminal detection and assumes that the terminal is only capable of standard ANSI formatting.
 
 COLUMNS::
     The number of character columns on screen.
@@ -183,7 +209,7 @@ Unless `--no-colour` is given, mdcat translates CommonMark text into ANSI format
 It uses bold (SGR 1), italic (SGR 3) and strikethrough (SGR 9) formatting, and the standard 4-bit color sequences, as well as https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda[OSC 8] for hyperlinks.
 It does not use 8-bit or 24-bit color sequences, though this may change in future releases.
 
-Additionally, it uses proprietary escape code if it detects specific terminal emulators:
+Additionally, it uses proprietary escape code if it detects one of the following terminal emulators (see <<Terminal detection>> and <<Environment>> for details):
 
 * https://iterm2.com/[iTerm2]: Inline images (https://iterm2.com/documentation-images.html[iTerm2 protocol]) and
 https://iterm2.com/documentation-escape-codes.html[Marks].

src/bin/mdcat/main.rs

@@ -21,8 +21,9 @@ use tracing_subscriber::filter::LevelFilter;
 use tracing_subscriber::EnvFilter;
 
 use crate::output::Output;
+use mdcat::terminal::{TerminalProgram, TerminalSize};
+use mdcat::ResourceAccess;
 use mdcat::{Environment, Settings};
-use mdcat::{ResourceAccess, TerminalCapabilities, TerminalSize};
 
 mod args;
 mod output;
@@ -102,21 +103,17 @@ fn main() {
     let args = Args::parse().command;
     event!(target: "mdcat::main", Level::TRACE, ?args, "mdcat arguments");
 
-    let terminal_capabilities = if args.no_colour {
-        // If the user disabled colours assume a dumb terminal
-        TerminalCapabilities::none()
+    let terminal = if args.no_colour {
+        TerminalProgram::Dumb
     } else if args.paginate() || args.ansi_only {
         // A pager won't support any terminal-specific features
-        TerminalCapabilities::ansi()
+        TerminalProgram::Ansi
     } else {
-        TerminalCapabilities::detect()
+        TerminalProgram::detect()
     };
 
-    let size = TerminalSize::detect().unwrap_or_default();
-    let columns = args.columns.unwrap_or(size.columns);
-
     if args.detect_only {
-        println!("Terminal: {}", terminal_capabilities.name);
+        println!("Terminal: {terminal}");
     } else {
         // On Windows 10 we need to enable ANSI term explicitly.
         #[cfg(windows)]
@@ -125,10 +122,13 @@ fn main() {
             ansi_term::enable_ansi_support().ok();
         }
 
+        let size = TerminalSize::detect().unwrap_or_default();
+        let columns = args.columns.unwrap_or(size.columns);
+
         let exit_code = match Output::new(args.paginate()) {
             Ok(mut output) => {
                 let settings = Settings {
-                    terminal_capabilities,
+                    terminal_capabilities: terminal.capabilities(),
                     terminal_size: TerminalSize { columns, ..size },
                     resource_access: if args.local_only {
                         ResourceAccess::LocalOnly

src/lib.rs

@@ -18,14 +18,15 @@ use tracing::instrument;
 
 // Expose some select things for use in main
 pub use crate::resources::ResourceAccess;
-pub use crate::terminal::*;
+use crate::terminal::capabilities::TerminalCapabilities;
+use crate::terminal::TerminalSize;
 use url::Url;
 
 mod magic;
 mod references;
 mod resources;
 mod svg;
-mod terminal;
+pub mod terminal;
 
 mod render;
 
@@ -143,6 +144,7 @@ mod tests {
         use pretty_assertions::assert_eq;
         use syntect::parsing::SyntaxSet;
 
+        use crate::terminal::TerminalProgram;
         use crate::*;
 
         use super::render_string;
@@ -153,7 +155,7 @@ mod tests {
                 &Settings {
                     resource_access: ResourceAccess::LocalOnly,
                     syntax_set: SyntaxSet::default(),
-                    terminal_capabilities: TerminalCapabilities::none(),
+                    terminal_capabilities: TerminalProgram::Dumb.capabilities(),
                     terminal_size: TerminalSize::default(),
                 },
             )
@@ -286,6 +288,7 @@ Hello Donald[2]
         use pretty_assertions::assert_eq;
         use syntect::parsing::SyntaxSet;
 
+        use crate::terminal::TerminalProgram;
         use crate::*;
 
         use super::render_string;
@@ -296,7 +299,7 @@ Hello Donald[2]
                 &Settings {
                     resource_access: ResourceAccess::LocalOnly,
                     syntax_set: SyntaxSet::default(),
-                    terminal_capabilities: TerminalCapabilities::none(),
+                    terminal_capabilities: TerminalProgram::Dumb.capabilities(),
                     terminal_size: TerminalSize::default(),
                 },
             )

src/render.rs

@@ -31,6 +31,7 @@ use state::*;
 use write::*;
 
 use crate::render::state::MarginControl::{Margin, NoMargin};
+use crate::terminal::capabilities::LinkCapability;
 pub use data::StateData;
 pub use state::State;
 pub use state::StateAndData;
@@ -607,7 +608,7 @@ pub fn write_event<'a, W: Write>(
         // Images
         (Stacked(stack, Inline(state, attrs)), Start(Image(_, link, _))) => {
             let InlineAttrs { style, indent } = attrs;
-            use ImageCapability::*;
+            use crate::terminal::capabilities::ImageCapability::*;
             let resolved_link = environment.resolve_reference(&link);
             let image_state = match (settings.terminal_capabilities.image, resolved_link) {
                 (Some(Terminology(terminology)), Some(ref url)) => {

src/render/state.rs

@@ -4,7 +4,8 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-use crate::{AnsiStyle, LinkCapability};
+use crate::terminal::capabilities::LinkCapability;
+use crate::terminal::AnsiStyle;
 use ansi_term::Style;
 use std::borrow::Borrow;
 use syntect::highlighting::HighlightState;

src/render/write.rs

@@ -14,9 +14,9 @@ use syntect::parsing::{ParseState, ScopeStack};
 use crate::references::*;
 use crate::render::data::LinkReferenceDefinition;
 use crate::render::state::*;
-use crate::{
-    Environment, MarkCapability, Settings, StyleCapability, TerminalCapabilities, TerminalSize,
-};
+use crate::terminal::capabilities::{MarkCapability, StyleCapability, TerminalCapabilities};
+use crate::terminal::TerminalSize;
+use crate::{Environment, Settings};
 
 #[inline]
 pub fn write_indent<W: Write>(writer: &mut W, level: u16) -> Result<()> {
@@ -86,7 +86,7 @@ pub fn write_link_refs<W: Write>(
             // clickable.  This mostly helps images inside inline links which we had to write as
             // reference links because we can't nest inline links.
             if let Some(url) = environment.resolve_reference(&link.target) {
-                use crate::LinkCapability::*;
+                use crate::terminal::capabilities::LinkCapability::*;
                 match &capabilities.links {
                     Some(Osc8(links)) => {
                         links.set_link_url(writer, url, &environment.hostname)?;