Add per-file comment markers to the postprocessing InputSig

The `--learn` support that follows needs to render inline-expectation
comments in the syntax of the file being edited, and a single CodeQL
database can mix source languages (e.g. Java plus XML), so the marker
must be chosen per file rather than per database.

Extend `TestPostProcessing::InputSig` with `getStartCommentMarker(relativePath)`
(no result -> that file is left untouched by `--learn`) and a defaulted
`getEndCommentMarker(relativePath)` (`none()` by default: line-comment
languages render no closing marker; block-comment languages can override
it later). Each language's `InlineExpectationsTestQuery.ql` implements
`getStartCommentMarker`, gated to that language's own source extensions so
that other file types (XML/YAML/HTML/ERB/Razor) extracted into the same
database are not rewritten with the wrong syntax.

This commit only wires the marker API through the signature and the
per-language inputs; nothing consumes it yet, so behavior is unchanged.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 1adfa307-c48e-43f5-94e3-8286e4a8c083

Author: d10c

cpp/ql/lib/utils/test/InlineExpectationsTestQuery.ql

@@ -18,4 +18,13 @@ private module Input implements T::TestPostProcessing::InputSig<Impl> {
         f.getRelativePath() + ":" + startline + ":" + startcolumn + ":" + endline + ":" + endcolumn
     )
   }
+
+  bindingset[relativePath]
+  string getStartCommentMarker(string relativePath) {
+    // C/C++ databases can also contain XML (e.g. `.xml`, `.props`), whose block-comment
+    // syntax is not yet supported, so we only render for C/C++ sources.
+    relativePath
+        .regexpMatch(".*\\.(c|cc|cpp|cxx|cp|c\\+\\+|h|hh|hpp|hxx|h\\+\\+|inl|tcc|ipp|tpp|cu|cuh)") and
+    result = "//"
+  }
 }

csharp/ql/lib/utils/test/InlineExpectationsTestQuery.ql

@@ -18,4 +18,12 @@ private module Input implements T::TestPostProcessing::InputSig<Impl> {
         f.getRelativePath() + ":" + startline + ":" + startcolumn + ":" + endline + ":" + endcolumn
     )
   }
+
+  bindingset[relativePath]
+  string getStartCommentMarker(string relativePath) {
+    // C# databases can also contain XML (e.g. `.csproj`, `.config`) and Razor markup, whose
+    // comment syntaxes are not yet supported, so we only render for C# sources.
+    relativePath.regexpMatch(".*\\.(cs|csx)") and
+    result = "//"
+  }
 }

go/ql/lib/utils/test/InlineExpectationsTestQuery.ql

@@ -18,4 +18,12 @@ private module Input implements T::TestPostProcessing::InputSig<Impl> {
         f.getRelativePath() + ":" + startline + ":" + startcolumn + ":" + endline + ":" + endcolumn
     )
   }
+
+  bindingset[relativePath]
+  string getStartCommentMarker(string relativePath) {
+    // Go databases can also contain XML, whose block-comment syntax is not yet supported, so
+    // we only render for Go sources.
+    relativePath.matches("%.go") and
+    result = "//"
+  }
 }

java/ql/lib/utils/test/InlineExpectationsTestQuery.ql

@@ -18,4 +18,12 @@ private module Input implements T::TestPostProcessing::InputSig<Impl> {
         f.getRelativePath() + ":" + startline + ":" + startcolumn + ":" + endline + ":" + endcolumn
     )
   }
+
+  bindingset[relativePath]
+  string getStartCommentMarker(string relativePath) {
+    // Java databases can also contain XML; those files use a different (block) comment
+    // syntax that is not yet supported, so we only render for Java and Kotlin sources.
+    (relativePath.matches("%.java") or relativePath.matches("%.kt")) and
+    result = "//"
+  }
 }

javascript/ql/lib/utils/test/InlineExpectationsTestQuery.ql

@@ -18,4 +18,12 @@ private module Input implements T::TestPostProcessing::InputSig<Impl> {
         f.getRelativePath() + ":" + startline + ":" + startcolumn + ":" + endline + ":" + endcolumn
     )
   }
+
+  bindingset[relativePath]
+  string getStartCommentMarker(string relativePath) {
+    // JavaScript databases can also contain HTML, whose (block) comment syntax is not yet
+    // supported, so we only render for the line-comment source files.
+    relativePath.regexpMatch(".*\\.(js|cjs|mjs|jsx|ts|cts|mts|tsx)") and
+    result = "//"
+  }
 }

python/ql/lib/utils/test/InlineExpectationsTestQuery.ql

@@ -18,4 +18,12 @@ private module Input implements T::TestPostProcessing::InputSig<Impl> {
         f.getRelativePath() + ":" + startline + ":" + startcolumn + ":" + endline + ":" + endcolumn
     )
   }
+
+  bindingset[relativePath]
+  string getStartCommentMarker(string relativePath) {
+    // Python databases can also contain XML, whose block-comment syntax is not yet supported,
+    // so we only render for Python sources.
+    relativePath.regexpMatch(".*\\.(py|pyi)") and
+    result = "#"
+  }
 }

ql/ql/src/utils/test/InlineExpectationsTestQuery.ql

@@ -18,4 +18,12 @@ private module Input implements T::TestPostProcessing::InputSig<Impl> {
         f.getRelativePath() + ":" + startline + ":" + startcolumn + ":" + endline + ":" + endcolumn
     )
   }
+
+  bindingset[relativePath]
+  string getStartCommentMarker(string relativePath) {
+    // The QL extractor can also extract YAML (e.g. `qlpack.yml`), whose `#` comment syntax
+    // differs, so we only render for QL sources and dbscheme files.
+    relativePath.regexpMatch(".*\\.(ql|qll|dbscheme)") and
+    result = "//"
+  }
 }

ruby/ql/lib/utils/test/InlineExpectationsTestQuery.ql

@@ -18,4 +18,12 @@ private module Input implements T::TestPostProcessing::InputSig<Impl> {
         f.getRelativePath() + ":" + startline + ":" + startcolumn + ":" + endline + ":" + endcolumn
     )
   }
+
+  bindingset[relativePath]
+  string getStartCommentMarker(string relativePath) {
+    // Ruby databases can also contain ERB, whose comment syntax is not yet supported, so we
+    // only render for plain Ruby sources.
+    relativePath.matches("%.rb") and
+    result = "#"
+  }
 }

rust/ql/lib/utils/test/InlineExpectationsTestQuery.ql

@@ -18,4 +18,12 @@ private module Input implements T::TestPostProcessing::InputSig<Impl> {
         f.getRelativePath() + ":" + startline + ":" + startcolumn + ":" + endline + ":" + endcolumn
     )
   }
+
+  bindingset[relativePath]
+  string getStartCommentMarker(string relativePath) {
+    // Rust databases can also contain YAML, whose `#` comment syntax differs, so we only
+    // render for Rust sources.
+    relativePath.matches("%.rs") and
+    result = "//"
+  }
 }

shared/util/codeql/util/test/InlineExpectationsTest.qll

@@ -655,6 +655,28 @@ module TestPostProcessing {
 
   signature module InputSig<InlineExpectationsTestSig Input> {
     string getRelativeUrl(Input::Location location);
+
+    /**
+     * Gets the marker that starts a line comment (for example `"//"` or `"#"`) in the source
+     * file with the given `relativePath`, provided that `codeql test run --learn` is able to
+     * render inline expectations for that file. Files for which this has no result are left
+     * untouched by `--learn`.
+     *
+     * This is keyed on the file rather than on the analyzed language because a single database
+     * may contain source files in several languages with different comment syntaxes (for
+     * example Java together with XML). `relativePath` is the path reported by `getRelativeUrl`.
+     */
+    bindingset[relativePath]
+    string getStartCommentMarker(string relativePath);
+
+    /**
+     * Gets the marker that ends a comment (for example `"-->"`) in the source file with the
+     * given `relativePath`. Has no result by default, which is correct for languages whose
+     * inline expectations use line comments (so `--learn` renders no closing marker);
+     * block-comment languages can override it so that `--learn` renders a closing marker.
+     */
+    bindingset[relativePath]
+    default string getEndCommentMarker(string relativePath) { none() }
   }
 
   module Make<InlineExpectationsTestSig Input, InputSig<Input> Input2> {