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/internal/InlineExpectationsTestImpl.qll

@@ -35,4 +35,13 @@ module Impl implements InlineExpectationsTestSig {
         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/internal/InlineExpectationsTestImpl.qll

@@ -59,4 +59,12 @@ module Impl implements InlineExpectationsTestSig {
         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/internal/InlineExpectationsTestImpl.qll

@@ -30,4 +30,12 @@ module Impl implements InlineExpectationsTestSig {
         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/internal/InlineExpectationsTestImpl.qll

@@ -45,4 +45,12 @@ module Impl implements InlineExpectationsTestSig {
         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", "%.kt"]) and
+    result = "//"
+  }
 }

javascript/ql/lib/utils/test/internal/InlineExpectationsTestImpl.qll

@@ -18,6 +18,14 @@ module Impl implements InlineExpectationsTestSig {
     )
   }
 
+  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 line-comment source files.
+    relativePath.regexpMatch(".*\\.(js|cjs|mjs|jsx|ts|cts|mts|tsx)") and
+    result = "//"
+  }
+
   abstract private class ExpectationCommentImpl extends Locatable {
     abstract string getContents();
 

python/ql/lib/utils/test/internal/InlineExpectationsTestImpl.qll

@@ -19,4 +19,12 @@ module Impl implements InlineExpectationsTestSig {
         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/internal/InlineExpectationsTestImpl.qll

@@ -35,4 +35,12 @@ module Impl implements InlineExpectationsTestSig {
         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/internal/InlineExpectationsTestImpl.qll

@@ -46,4 +46,12 @@ module Impl implements InlineExpectationsTestSig {
         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/internal/InlineExpectationsTestImpl.qll

@@ -21,4 +21,12 @@ module Impl implements InlineExpectationsTestSig {
         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

@@ -111,6 +111,28 @@ signature module InlineExpectationsTestSig {
   /** Gets the relative URL of the given location, if any. */
   string getRelativeUrl(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() }
+
   /** A comment that may contain inline expectations. */
   class ExpectationComment {
     /** Gets the contents of this comment, _excluding_ the comment indicator. */
@@ -748,6 +770,16 @@ module TestPostProcessing {
 
       string getRelativeUrl(Location location) { result = location.getRelativeUrl() }
 
+      bindingset[relativePath]
+      string getStartCommentMarker(string relativePath) {
+        result = Input::getStartCommentMarker(relativePath)
+      }
+
+      bindingset[relativePath]
+      string getEndCommentMarker(string relativePath) {
+        result = Input::getEndCommentMarker(relativePath)
+      }
+
       final private class ExpectationCommentFinal = Input::ExpectationComment;
 
       class ExpectationComment extends ExpectationCommentFinal {