From 9fae50ed4be6c7f8bd16ece9626709d78bb4b01c Mon Sep 17 00:00:00 2001
From: Silvan Mosberger <silvan.mosberger@tweag.io>
Date: Wed, 17 Jul 2024 02:42:18 +0200
Subject: [PATCH 1/2] Add parser test for indented strings

So that in the next commit we can see what changes about this test
---
 .../functional/lang/parse-okay-ind-string.exp |  1 +
 .../functional/lang/parse-okay-ind-string.nix | 31 +++++++++++++++++++
 2 files changed, 32 insertions(+)
 create mode 100644 tests/functional/lang/parse-okay-ind-string.exp
 create mode 100644 tests/functional/lang/parse-okay-ind-string.nix

diff --git a/tests/functional/lang/parse-okay-ind-string.exp b/tests/functional/lang/parse-okay-ind-string.exp
new file mode 100644
index 000000000..5f8d48688
--- /dev/null
+++ b/tests/functional/lang/parse-okay-ind-string.exp
@@ -0,0 +1 @@
+(let string = "str"; in [ (/some/path) ((/some/path)) (("" + /some/path)) ((/some/path + "\n    end")) (string) ((string)) (("" + string)) ((string + "\n    end")) ("") ("") ("end") ])
diff --git a/tests/functional/lang/parse-okay-ind-string.nix b/tests/functional/lang/parse-okay-ind-string.nix
new file mode 100644
index 000000000..97c9de3cd
--- /dev/null
+++ b/tests/functional/lang/parse-okay-ind-string.nix
@@ -0,0 +1,31 @@
+let
+  string = "str";
+in [
+  /some/path
+
+  ''${/some/path}''
+
+  ''
+    ${/some/path}''
+
+  ''${/some/path}
+    end''
+
+  string
+
+  ''${string}''
+
+  ''
+    ${string}''
+
+  ''${string}
+    end''
+
+  ''''
+
+  ''
+  ''
+
+  ''
+    end''
+]

From 0c91bb97e5579169fdac94ebfbb352ee1cc4a5ae Mon Sep 17 00:00:00 2001
From: Silvan Mosberger <silvan.mosberger@tweag.io>
Date: Wed, 17 Jul 2024 02:43:42 +0200
Subject: [PATCH 2/2] parser: Remove empty multiline string parts earlier

Makes parsing more consistent and is a super minor optimisation

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
---
 src/libexpr/parser-state.hh                     | 13 ++++++++++++-
 tests/functional/lang/parse-okay-ind-string.exp |  2 +-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/libexpr/parser-state.hh b/src/libexpr/parser-state.hh
index 983a17a2e..d8287db9b 100644
--- a/src/libexpr/parser-state.hh
+++ b/src/libexpr/parser-state.hh
@@ -291,12 +291,23 @@ inline Expr * ParserState::stripIndentation(const PosIdx pos,
                 s2 = std::string(s2, 0, p + 1);
         }
 
-        es2->emplace_back(i->first, new ExprString(std::move(s2)));
+        // Ignore empty strings for a minor optimisation and AST simplification
+        if (s2 != "") {
+            es2->emplace_back(i->first, new ExprString(std::move(s2)));
+        }
     };
     for (; i != es.end(); ++i, --n) {
         std::visit(overloaded { trimExpr, trimString }, i->second);
     }
 
+    // If there is nothing at all, return the empty string directly.
+    // This also ensures that equivalent empty strings result in the same ast, which is helpful when testing formatters.
+    if (es2->size() == 0) {
+        auto *const result = new ExprString("");
+        delete es2;
+        return result;
+    }
+
     /* If this is a single string, then don't do a concatenation. */
     if (es2->size() == 1 && dynamic_cast<ExprString *>((*es2)[0].second)) {
         auto *const result = (*es2)[0].second;
diff --git a/tests/functional/lang/parse-okay-ind-string.exp b/tests/functional/lang/parse-okay-ind-string.exp
index 5f8d48688..82e9940a2 100644
--- a/tests/functional/lang/parse-okay-ind-string.exp
+++ b/tests/functional/lang/parse-okay-ind-string.exp
@@ -1 +1 @@
-(let string = "str"; in [ (/some/path) ((/some/path)) (("" + /some/path)) ((/some/path + "\n    end")) (string) ((string)) (("" + string)) ((string + "\n    end")) ("") ("") ("end") ])
+(let string = "str"; in [ (/some/path) ((/some/path)) ((/some/path)) ((/some/path + "\n    end")) (string) ((string)) ((string)) ((string + "\n    end")) ("") ("") ("end") ])