From 113ed1a871fddae8ccf942c19fe6737106fb3e84 Mon Sep 17 00:00:00 2001
From: Lars Wirzenius <liw@liw.fi>
Date: Sun, 14 May 2023 07:46:35 +0300
Subject: feat: check for duplicate scenario titles

Sponsored-by: author
---
 src/doc.rs   | 13 +++++++++++++
 src/error.rs |  7 +++++++
 subplot.md   | 42 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 62 insertions(+)

diff --git a/src/doc.rs b/src/doc.rs
index 640968c..f08f795 100644
--- a/src/doc.rs
+++ b/src/doc.rs
@@ -265,12 +265,25 @@ impl Document {
     pub fn lint(&self) -> Result<(), SubplotError> {
         trace!("Linting document");
         self.check_doc_has_title()?;
+        self.check_scenarios_are_unique()?;
         self.check_filenames_are_unique()?;
         self.check_block_classes()?;
         trace!("No linting problems found");
         Ok(())
     }
 
+    // Check that all titles for scenarios are unique.
+    fn check_scenarios_are_unique(&self) -> Result<(), SubplotError> {
+        let mut known = HashSet::new();
+        for title in self.scenarios()?.iter().map(|s| s.title().to_lowercase()) {
+            if known.contains(&title) {
+                return Err(SubplotError::DuplicateScenario(title));
+            }
+            known.insert(title);
+        }
+        Ok(())
+    }
+
     // Check that all filenames for embedded files are unique.
     fn check_filenames_are_unique(&self) -> Result<(), SubplotError> {
         let mut known = HashSet::new();
diff --git a/src/error.rs b/src/error.rs
index a322bd6..f7dfe52 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -173,6 +173,13 @@ pub enum SubplotError {
     #[error("continuation keyword used too early")]
     ContinuationTooEarly,
 
+    /// Scenario has the same title as another scenario
+    ///
+    /// Titles of scenarios must be unique in the input document,
+    /// but Subplot found at least one with the same title as another.
+    #[error("Scenario title is duplicate: {0:?}")]
+    DuplicateScenario(String),
+
     /// Embedded file has the same name as another embedded file
     ///
     /// Names of embedded files must be unique in the input document,
diff --git a/subplot.md b/subplot.md
index 8556afd..9929e8b 100644
--- a/subplot.md
+++ b/subplot.md
@@ -1309,6 +1309,48 @@ then bar was done
 ```
 ~~~~
 
+## Duplicate scenario titles
+
+_Requirement: Subplot treats it as an error if two scenarios have the
+same title._
+
+Justification: the title is how a scenario is identified, and the user
+needs to be able to do so unambiguously.
+
+~~~scenario
+given file duplicate-scenario-titles.subplot
+given file duplicate-scenario-titles.md
+given file b.yaml
+given file f.py
+given an installed subplot
+when I try to run subplot metadata duplicate-scenario-titles.subplot
+then command fails
+then stderr contains "duplicate"
+~~~
+
+~~~~{#duplicate-scenario-titles.subplot .file .yaml .numberLines}
+title: Test scenario
+markdowns:
+- duplicate-scenario-titles.md
+bindings: [b.yaml]
+impls:
+  python: [f.py]
+~~~~
+
+~~~~{#duplicate-scenario-titles.md .file .markdown .numberLines}
+# My sceanrio
+
+```scenario
+when I do bar
+```
+
+# My sceanrio
+
+```scenario
+when I do bar
+```
+~~~~
+
 ## Empty lines in scenarios
 
 This scenario verifies that empty lines in scenarios are OK.
-- 
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