fix: latent parsing bugs in fs_patch and argc

assets/functions/tools/fs_patch.sh

@@ -14,6 +14,11 @@ set -e
 #   is the most common cause of "unable to apply patch" failures, especially in files with sed/jq/regex pipelines or
 #   embedded Python with quoted strings.
 # - Hunks are applied in order; the first hunk that fails aborts the whole patch — later hunks are NOT attempted.
+# - Hunks anchor at the FIRST exact match of their context in the file, so include enough context to make each hunk
+#   unique. Hunks must appear in file order.
+# - Every hunk needs at least one context or removed line to anchor it; a hunk containing only additions is an error.
+# - Unrecognized lines inside a hunk are hard errors: every hunk line must start with ' ' (context), '-' (removal),
+#   or '+' (addition).
 # - If you've edited this file in earlier tool calls, fs_cat it again before composing the patch. A stale view of the file
 #   produces context lines that no longer match.
 # - On failure the error message names the failing hunk and shows the expected-vs-actual line. Fix that specific line and
@@ -50,6 +55,14 @@ main() {
 		# status so a failure still aborts under `set -e`.
 		new_contents="$(patch_file "$argc_path" <(printf "%s" "$argc_contents"); rc=$?; printf x; exit "$rc")"
 		new_contents="${new_contents%x}"
+
+		# awk newline-terminates every printed line, so patching a file that lacks
+		# a final newline would silently add one. Preserve the original file's
+		# final-newline state instead.
+		if [[ -n "$(tail -c 1 "$argc_path")" ]]; then
+			new_contents="${new_contents%$'\n'}"
+		fi
+
     printf "%s" "$new_contents" | git diff --no-index "$argc_path" - || true
 
     guard_operation "Apply changes?"

assets/functions/utils/prompt-utils.sh

@@ -528,7 +528,11 @@ guard_operation() {
 # +    print(f"Hello {name}")
 patch_file() {
   awk '
-    FNR == NR {
+    function isHeaderPair(i) {
+      return (patchLines[i] ~ /^--- / && patchLines[i+1] ~ /^\+\+\+ / && patchLines[i+2] ~ /^@@/)
+    }
+
+    FILENAME == ARGV[1] {
       lines[FNR] = $0
       next;
     }
@@ -547,11 +551,6 @@ patch_file() {
       while (patchLineIndex <= totalPatchLines) {
         line = patchLines[patchLineIndex]
 
-        if (line ~ /^--- / || line ~ /^\+\+\+ /) {
-          patchLineIndex++
-          continue
-        }
-
         if (line ~ /^@@/) {
           mode = "hunk"
           hunkIndex++
@@ -560,7 +559,22 @@ patch_file() {
         }
 
         if (mode == "hunk") {
-          while (patchLineIndex <= totalPatchLines && line ~ /^[-+ ]|^\s*$/ && line !~ /^--- /) {
+          while (patchLineIndex <= totalPatchLines) {
+            line = patchLines[patchLineIndex]
+
+            if (line ~ /^\\ No newline/) {
+              patchLineIndex++
+              continue
+            }
+
+            if (isHeaderPair(patchLineIndex)) {
+              break
+            }
+
+            if (line !~ /^[-+ ]/ && line !~ /^[ \t]*$/) {
+              break
+            }
+
             sanitizedLine = substr(line, 2)
 
             if (line !~ /^\+/) {
@@ -574,13 +588,37 @@ patch_file() {
             }
 
             patchLineIndex++
-            line = patchLines[patchLineIndex]
           }
 
           mode = "none"
-        } else {
+          continue
-          patchLineIndex++
         }
+
+        if (isHeaderPair(patchLineIndex)) {
+          patchLineIndex += 2
+          continue
+        }
+
+        if (line ~ /^\\ No newline/) {
+          patchLineIndex++
+          continue
+        }
+
+        if (hunkIndex == 0) {
+          # Preamble before the first hunk: tolerate prose, code fences, and lone headers.
+          patchLineIndex++
+          continue
+        }
+
+        if (line ~ /^[ \t]*$/ || line ~ /^```/) {
+          patchLineIndex++
+          continue
+        }
+
+        print "error: unrecognized line in patch (line " patchLineIndex "): " line > "/dev/stderr"
+        print "" > "/dev/stderr"
+        print "Every line inside a hunk must start with \" \" (context), \"-\" (removal), or \"+\" (addition)." > "/dev/stderr"
+        exit 1
       }
 
       if (hunkIndex == 0) {
@@ -593,6 +631,36 @@ patch_file() {
       }
 
       totalHunks = hunkIndex
+
+      if (totalLines == 0) {
+        for (h = 1; h <= totalHunks; h++) {
+          if (hunkTotalOriginalLines[h] > 0) {
+            print "error: unable to apply patch" > "/dev/stderr"
+            print "" > "/dev/stderr"
+            print "Hunk " h " expects existing content but the file is empty." > "/dev/stderr"
+            exit 1
+          }
+        }
+
+        for (h = 1; h <= totalHunks; h++) {
+          for (i = 1; i <= hunkTotalUpdatedLines[h]; i++) {
+            print hunkUpdatedLines[h,i]
+          }
+        }
+
+        exit 0
+      }
+
+      for (h = 1; h <= totalHunks; h++) {
+        if (hunkTotalOriginalLines[h] == 0) {
+          print "error: unable to apply patch" > "/dev/stderr"
+          print "" > "/dev/stderr"
+          print "Hunk " h " contains no context or removed lines; include at least one" > "/dev/stderr"
+          print "context line so the hunk can be anchored." > "/dev/stderr"
+          exit 1
+        }
+      }
+
       hunkIndex = 1
 
       for (lineIndex = 1; lineIndex <= totalLines; lineIndex++) {
@@ -603,7 +671,7 @@ patch_file() {
           nextLineIndex = lineIndex + 1
 
           for (i = 2; i <= hunkTotalOriginalLines[hunkIndex]; i++) {
-            if (lines[nextLineIndex] != hunkOriginalLines[hunkIndex,i]) {
+            if (nextLineIndex > totalLines || lines[nextLineIndex] != hunkOriginalLines[hunkIndex,i]) {
               if (i - 1 > bestPartialLen[hunkIndex]) {
                 bestPartialLen[hunkIndex] = i - 1
                 bestPartialAnchorLine[hunkIndex] = lineIndex
@@ -646,9 +714,13 @@ patch_file() {
             print "" > "/dev/stderr"
             print "Closest match: anchored at file line " bestPartialAnchorLine[failingHunk] ", matched " bestPartialLen[failingHunk] " of " hunkTotalOriginalLines[failingHunk] " original lines before diverging." > "/dev/stderr"
             print "" > "/dev/stderr"
-            print "At file line " bestPartialDivergeLine[failingHunk] " (hunk original line " bestPartialHunkPos[failingHunk] "):" > "/dev/stderr"
+            if (bestPartialDivergeLine[failingHunk] > totalLines) {
-            print "  expected: " bestPartialExpected[failingHunk] > "/dev/stderr"
+              print "The hunk expects additional lines beyond the end of the file (file has " totalLines " lines)." > "/dev/stderr"
-            print "  actual:   " bestPartialActual[failingHunk] > "/dev/stderr"
+            } else {
+              print "At file line " bestPartialDivergeLine[failingHunk] " (hunk original line " bestPartialHunkPos[failingHunk] "):" > "/dev/stderr"
+              print "  expected: " bestPartialExpected[failingHunk] > "/dev/stderr"
+              print "  actual:   " bestPartialActual[failingHunk] > "/dev/stderr"
+            }
           }
 
           print "" > "/dev/stderr"

src/parsers/bash.rs

@@ -23,6 +23,7 @@ pub fn generate_bash_declarations(
         "",
         env::var("TERM_WIDTH").ok().and_then(|v| v.parse().ok()),
     )?;
+    let build_script = allow_empty_required_values(&build_script);
     fs::write(tools_file_path, &build_script)
         .with_context(|| format!("Failed to write built script to '{tools_file_path:?}'"))?;
 
@@ -74,6 +75,20 @@ fn underscore(s: &str) -> String {
     s.replace('-', "_")
 }
 
+/// argc's generated required-param check uses `-z "${!name:-}"`, which
+/// conflates "not provided" with "provided but empty", so a required option
+/// passed an explicit empty string (e.g. `fs_write --content=''` to create an
+/// empty file) is rejected as "required arguments were not provided". The
+/// JSON schema we advertise to models treats `required` as *presence*, so
+/// rewrite the check to a set-ness test to keep runtime behavior consistent
+/// with the schema. Applied post-build so it survives every regeneration.
+fn allow_empty_required_values(build_script: &str) -> String {
+    build_script.replace(
+        r#"if [[ -z "${!name:-}" ]]; then"#,
+        r#"if [[ -z "${!name+x}" ]]; then"#,
+    )
+}
+
 fn schema_ty(t: &str) -> JsonSchema {
     JsonSchema {
         type_value: Some(t.to_string()),
@@ -147,3 +162,23 @@ fn parse_parameters_schema(flags: &[FlagOptionValue]) -> JsonSchema {
         required: Some(required),
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn rewrites_argc_required_check_to_setness_test() {
+        let src = "# @describe test tool\n# @option --content! The content\nmain() { :; }\n";
+        let built = argc::build(src, "", None).expect("argc build failed");
+        assert!(
+            built.contains(r#"if [[ -z "${!name:-}" ]]; then"#),
+            "argc changed its generated required-param template; update allow_empty_required_values()"
+        );
+
+        let fixed = allow_empty_required_values(&built);
+
+        assert!(fixed.contains(r#"if [[ -z "${!name+x}" ]]; then"#));
+        assert!(!fixed.contains(r#"if [[ -z "${!name:-}" ]]; then"#));
+    }
+}