feat: Add the `starship explain` command (#699)

This adds the explain argument to Starship, which explains what the printed modules in the prompt are.

1 files changed, 98 insertions, 21 deletions

diff --git a/src/print.rs b/src/print.rs
index 70826827f..ee3b36662 100644
--- a/src/print.rs
+++ b/src/print.rs
@@ -2,6 +2,7 @@ use clap::ArgMatches;
 use rayon::prelude::*;
 use std::fmt::Write as FmtWrite;
 use std::io::{self, Write};
+use unicode_width::UnicodeWidthChar;
 
 use crate::context::Context;
 use crate::module::Module;
@@ -26,27 +27,7 @@ pub fn get_prompt(context: Context) -> String {
 
     buf.push_str("\x1b[J");
 
-    let mut prompt_order: Vec<&str> = Vec::new();
-
-    // Write out a custom prompt order
-    for module in config.prompt_order {
-        if ALL_MODULES.contains(&module) {
-            prompt_order.push(module);
-        } else {
-            log::debug!(
-                "Expected prompt_order to contain value from {:?}. Instead received {}",
-                ALL_MODULES,
-                module,
-            );
-        }
-    }
-
-    let modules = &prompt_order
-        .par_iter()
-        .filter(|module| !context.is_module_disabled_in_config(module))
-        .map(|module| modules::handle(module, &context)) // Compute modules
-        .flatten()
-        .collect::<Vec<Module>>(); // Remove segments set to `None`
+    let modules = compute_modules(&context);
 
     let mut print_without_prefix = true;
     let printable = modules.iter();
@@ -76,3 +57,99 @@ pub fn module(module_name: &str, args: ArgMatches) {
 
     print!("{}", module);
 }
+
+pub fn explain(args: ArgMatches) {
+    let context = Context::new(args);
+
+    struct ModuleInfo {
+        value: String,
+        value_len: usize,
+        desc: String,
+    }
+
+    let dont_print = vec!["line_break", "character"];
+
+    let modules = compute_modules(&context)
+        .into_iter()
+        .filter(|module| !dont_print.contains(&module.get_name().as_str()))
+        .map(|module| {
+            let ansi_strings = module.ansi_strings_for_prompt(false);
+            let value = module.get_segments().join("");
+            ModuleInfo {
+                value: ansi_term::ANSIStrings(&ansi_strings[1..ansi_strings.len() - 1]).to_string(),
+                value_len: value.chars().count() + count_wide_chars(&value),
+                desc: module.get_description().to_owned(),
+            }
+        })
+        .collect::<Vec<ModuleInfo>>();
+
+    let mut max_ansi_module_width = 0;
+    let mut max_module_width = 0;
+
+    for info in &modules {
+        max_ansi_module_width = std::cmp::max(
+            max_ansi_module_width,
+            info.value.chars().count() + count_wide_chars(&info.value),
+        );
+        max_module_width = std::cmp::max(max_module_width, info.value_len);
+    }
+
+    let desc_width = term_size::dimensions()
+        .map(|(w, _)| w)
+        .map(|width| width - std::cmp::min(width, max_ansi_module_width));
+
+    println!("\n Here's a breakdown of your prompt:");
+    for info in modules {
+        let wide_chars = count_wide_chars(&info.value);
+
+        if let Some(desc_width) = desc_width {
+            let wrapped = textwrap::fill(&info.desc, desc_width);
+            let mut lines = wrapped.split('\n');
+            println!(
+                " {:width$}  -  {}",
+                info.value,
+                lines.next().unwrap(),
+                width = max_ansi_module_width - wide_chars
+            );
+
+            for line in lines {
+                println!("{}{}", " ".repeat(max_module_width + 6), line.trim());
+            }
+        } else {
+            println!(
+                " {:width$}  -  {}",
+                info.value,
+                info.desc,
+                width = max_ansi_module_width - wide_chars
+            );
+        };
+    }
+}
+
+fn compute_modules<'a>(context: &'a Context) -> Vec<Module<'a>> {
+    let mut prompt_order: Vec<&str> = Vec::new();
+
+    // Write out a custom prompt order
+    for module in context.config.get_root_config().prompt_order {
+        if ALL_MODULES.contains(&module) {
+            prompt_order.push(module);
+        } else {
+            log::debug!(
+                "Expected prompt_order to contain value from {:?}. Instead received {}",
+                ALL_MODULES,
+                module,
+            );
+        }
+    }
+
+    prompt_order
+        .par_iter()
+        .filter(|module| !context.is_module_disabled_in_config(module))
+        .map(|module| modules::handle(module, &context)) // Compute modules
+        .flatten() // Remove segments set to `None`
+        .collect::<Vec<Module<'a>>>()
+}
+
+fn count_wide_chars(value: &str) -> usize {
+    value.chars().filter(|c| c.width().unwrap_or(0) > 1).count()
+}