feature: allow requiring select captures for output to show (#8)

CHANGELOG.md

@@ -3,6 +3,14 @@ All notable changes to this project will be documented in this file.
 
 This project adheres to [Semantic Versioning](http://semver.org/).
 
+## [0.2.0] - 2025-01-12
+
+Adds ability to require specified captures to have at least one match in order for output to show for a given line:
+
+```
+-r, --require <REQUIRE>          Name of capture that must have at least one match for the output to show. Can be specified multiple times
+```
+
 ## [0.1.0] - 2025-01-11
 
 First release

Cargo.toml

@@ -5,7 +5,7 @@ description = """
 A text line processor that applies regular expressions with named captures
 to input lines and transforms them using a user-generated template.
 """
-version = "0.1.0"
+version = "0.2.0"
 edition = "2021"
 readme = "README.md"
 license = "MIT"

src/cli.rs

@@ -165,7 +165,12 @@ pub struct Cli {
     /// Input files
     pub files: Vec<String>,
 
-    /// Force output to be line-buffered.  By default, output is line buffered when stdout is a
+    /// Name of capture that must have at least one match for the output to show. Can be specified
+    /// multiple times
+    #[arg(short, long)]
+    pub require: Vec<String>,
+
+    /// Force output to be line-buffered. By default, output is line buffered when stdout is a
     /// terminal and block-buffered otherwise
     #[arg(long)]
     pub line_buffered: bool,

src/line.rs

@@ -15,6 +15,7 @@ pub fn process_lines(tty: &mut TtyContext, args: &Cli) -> Result<()> {
         template,
         files,
         line_buffered,
+        require,
         ..
     } = args;
 
@@ -55,7 +56,7 @@ pub fn process_lines(tty: &mut TtyContext, args: &Cli) -> Result<()> {
 
     let mut writer = init_output_writer(tty, *line_buffered);
 
-    for line in scanner {
+    'outer: for line in scanner {
         // Each iteration starts with a fresh captures map. Doing it this way the lifetime of the
         // new captures map contain the lifetime of `line`, allowing us to work with a `Vec<&str>`
         // as opposed to `Vec<String>`. There's no telling how many matches there could possibly be
@@ -76,6 +77,11 @@ pub fn process_lines(tty: &mut TtyContext, args: &Cli) -> Result<()> {
                 }
             }
         }
+        for capture_name in require {
+            if captures_map.get(capture_name.as_str()).is_none_or(|c| c.is_empty()) {
+                continue 'outer;
+            }
+        }
         let output_line = template.transform(&captures_map);
 
         if output_line.is_empty() {